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DIAGNOSIS

SYSTEM DIAGNOSIS

Diagnostic System Check

Test Description

The numbers below refer to the step numbers on the diagnostic table.
  1. This step insures that the battery, and the vehicle primary power and ground systems are functioning correctly.
  2. Lack of communication may be due to a particular malfunction of a serial data circuit.
  3. This step insures that all data link communication DTCs are diagnosed before system level DTCs.
  4. This step insures that all electronic control unit (ECU) internal DTCs are diagnosed before other system level DTCs.
  5. This step insures that all device voltage DTCs are diagnosed before other system level DTCs.

Diagnostic System Check

Step Action Value(s) Yes No
1
Perform the following preliminary inspections:
  • Ensure that the battery is fully charged.
  • Ensure that the battery cables are clean and tight.
  • Inspect for any open fuses.
  • Inspect the easily accessible systems or the visible system components for obvious damage or conditions that could cause the symptom.
  • Ensure that the grounds are clean, tight, and in the correct location.
  • Inspect for aftermarket devices that could affect the operation of the system.
  • Search for applicable service bulletins.
Did you find and correct the condition?
-
System OK
Go to Step 2
2
Install a scan tool.
Does the scan tool power up?
-
Go to Step 3
Go to Scan Tool Does Not Power Up
3
Attempt to start the engine.
Does the engine crank?
-
Go to Step 4
Refer to "No Crank" in 1E, Engine Electrical
4
Attempt to start the engine.
Does the engine start and idle?
-
Go to Step 5
Go to "Engine Cranks but Does Not Run"
5

Important : Do not clear any DTCs unless instructed by a diagnostic procedure.

Use the appropriate scan tool selections to obtain DTCs for each of the control modules.
Does the scan tool display any DTCs?
-
Go to Step 6
Go to "Symtoms – Engine Controls"
6
Does the scan tool display any DTCs that begin with a "U"?
-
Go to applicable DTC table
Go to Step 7
7

Important : If any of these DTCs are displayed, diagnose them before diagnosing any other DTCs or symptoms.

Does the scan tool display DTCs related to control module internal fault?
-
Go to applicable DTC table
Go to Step 8
8

Important : If any of these DTCs are displayed, diagnose them before diagnosing any other DTCs or symptoms.

Does the scan tool display DTCs related to the fault in the battery/ignition voltage supply to control module?
-
Go to applicable DTC table
Go to Step 9
9
If multiple DTCs are stored, diagnose the DTCs in the following order:
  1. Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs.
  2. System level DTCs, such as misfire DTCs, evaporative emission (EVAP) system DTCs, and fuel trim DTCs.
  3. Diagnose the remaining DTCs.
Is the customer concerned with the other symptoms?
-
Go to "Symtoms – Engine Controls"
System OK

Symptoms – Engine Controls

Important Preliminary Inspections Before Starting

Before using this section, perform the Diagnostic System Check in this section and verify all of the following conditions :

Visual and Physical Inspection

Inspect the following items :

Verify Customer's Concern

Locate the correct symptom table. Inspect the items indicated under that symptom from the following symptom tables:

Intermittent Conditions

Inspections
Action
Definition : The condition is not currently present but is indicated in DTC history.
Definition : OR
Definition : There is a customer concern, but the symptom cannot currently be duplicated, if the condition is not DTC related.
Preliminary
  • Refer to "Important Preliminary Inspection Before Starting" in Symptoms - Engine Controls.
  • The fault must be present to locate a problem using the DTC table. If a fault is intermittent, the use of DTC tables may result in the replacement of good parts.
Visual/Physical
This step is an important aid for locating a condition without extensive testing. Perform a thorough visual and physical inspection of the following components:
  • Wiring harness for damage or cuts
  • A misrouted harness that is too close to high voltage or high current devices such as the following:
    • Motors
    • Generators
  • Vacuum hoses for the following conditions:
    • Proper routing
    • Proper connections
    • Splits in the hose or the connections
    • Kinks
  • Air leaks for the following components:
    • Throttle body mounting
    • Intake manifold sealing surfaces
    • Air cleaner outlet
    • Manifold absolute pressure (MAP) sensor
    • Mass air flow (MAF) sensor
  • The control module and body grounds are clean and tight.
  • Battery connections are clean and tight
  • Charging system for proper operation.
Harness/Connector Test
Many intermittent open or shorted circuits come and go with harness and connector movement caused by vibration, engine torque, bumps and rough pavement, etc. Test for this type of condition by performing the applicable procedure from the following list:
  • Move the related connectors and wiring while monitoring the appropriate scan tool data.
  • Move the related connectors and wiring with the component commanded ON and OFF, with the scan tool. Observe the components operation.
  • With the engine running, move the related connectors and wiring while monitoring engine operation.
If harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary.
Electrical Connections or Wiring
Poor electrical connections and terminal tension or wiring faults cause most intermittents. Perform a careful inspection of the suspected circuit for the following:
  • Inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body, backed-out.
  • Inspect for improperly formed or damaged terminals. Test for incorrect terminal tension.
  • Inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
  • Inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits.
  • Inspect for wires that are broken inside the insulation.
  • Inspect the harness for pinched, cut, or rubbed through wiring.
  • Make sure the wiring does not come in contact with hot exhaust components.
Control Module Power and Grounds
Poor power or ground connections can cause widely varying symptoms.
  • Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Inspect connections at the control module connectors, fuses, and any intermediate connections between the power source and the control module or component. A test lamp or a DMM may indicate that voltage is present, but neither tests a circuits ability to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component.
  • Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Make sure the ground connections are clean and tight at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component.
Temperature Sensitivity
  • An intermittent condition may occur only when the component is cold, or only when the component is hot. The heat that affects the circuit can be engine generated or due to a poor connection in the circuit or a high electrical load.
  • Information from the customer may help to determine if the trouble follows a pattern that is temperature related. The Freeze Frame/Failure Records or Snapshot data may help with this type of intermittent condition, where applicable.
  • If the intermittent is related to heat, review the data for a relationship with the following:
    • High ambient temperatures
    • Underhood/engine generated heat
    • Circuit generated heat due to a poor connection, or high electrical load
    • Higher than normal load conditions (towing, etc.)
  • If the intermittent is related to cold, review the data for the following:
    • Low ambient temperatures
    • In extremely low temperatures, ice may form in a connection or component. Inspect for water intrusion.
    • The condition only occurs on a cold start.
    • The condition goes away when the vehicle warms up.
Electromagnetic Interference (EMI) and Electrical Noise
Some electrical components and circuits are sensitive to electromagnetic interference (EMI) or other types of electrical noise. Inspect for the following conditions:
  • A misrouted harness that is too close to high voltage and high current devices such as, motors, generator, etc. These components may induce electrical noise on a circuit that could interfere with normal circuit operation.
  • Electrical system interference caused by a malfunctioning relay, control module driven solenoid, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
  • Incorrect installation of non-factory, aftermarket, add-on accessories such as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm systems, cell phones, etc.
  • Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode or resistor.
Incorrect Control Module Programming
  • There are only a few situations where reprogramming a control module is appropriate:
    • A new control module is installed.
    • Revised software/calibration files have been released for this vehicle.

Important : DO NOT reprogram the control module with the SAME software/calibration files that are already present in the control module. This is not an effective repair for any type of driveability problem.

  • Verify that the control module contains the correct software/calibration. If incorrect programming is found, reprogram the control module with the most current software/calibration.
Duplicating Failure Conditions
If the previous tests were not successful, attempt to duplicate and/or capture the failure conditions.Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set.
  1. Review and record the Freeze Frame/Failure Records data.
  2. Clear any DTCs with a scan tool.
  3. Turn OFF the key and wait 15 seconds.
  4. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records. The vehicle must also be operating within the Conditions for Running the DTC. Refer to Conditions for Running the DTC in the supporting text of the DTC being diagnosed.
  5. Monitor DTC status for the DTC being tested. The scan tool will indicate Ran when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
An alternate method is to drive the vehicle with a DMM connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs may help you locate the problem.
Scan Tool Snapshot
The scan tool can be set up to take a snapshot of the parameters available via serial data. The Snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed or set up in advance to trigger when a DTC sets.
An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further.Refer to the scan tool user instructions for more information on the Snapshot function.

Hard Start

Inspections
Action
Definition : The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but immediately stops.
Preliminary Inspection
Sensor Inspection
  • Inspect the engine coolant temperature (ECT) sensor. Use the scan tool to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the ECT sensor circuit or the sensor itself.
  • Inspect the camshaft position (CMP) sensor and crankshaft position (CKP) sensor for proper mounting and/or a bad connection.
Fuel System Inspection
  • Inspect the fuel pump ralay operation. The fuel pump should turn ON for 2 seconds when the ignition is turned ON.
  • Inspect for leaking fuel injectors.
  • Inspect for plugged or restricted injectors.
  • Inspect for a contaminated fuel condition.
  • Inspect for a restricted fuel filter.
  • Inspect for low fuel pressure.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Correct heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the apsrk plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs.
Electrical System Inspection
Inspect for a slow cranking speed.
Air Intake System Inspection
  • Inspect the air cleaner and air intake ducts for a restrictions or leaks.
  • Inspect for a restriction or a leak in the intake manifolds.
Exhaust System Inspection
Inspect the exhaust system for a possible restriction.
Engine Mechanical Inspection
  • Inspect the engine for the following conditions:
    • Excessive oil in combustion chamber or leaking valve seals
    • Camshaft timing
    • Excessive carbon buildup in the combustion chambers
    • Improper valve timing
    • Bent pushrods
    • Worn rocker arms
    • Low engine compression
    • Broken or weak valve springs
    • Worn camshaft lobes
  • Inspect the following components for incorrect basic engine parts:
    • Camshafts
    • Cylinder head
    • Pistons, connecting rods, or bearings
Additional Inspection
  • Inspect for an intermittent CKP signal. Refer to Intermittent Conditions.
  • Inspect the Service Bulletins for control module software updates.

Surges/Chuggles

Inspections
Action
Definition : The engine has a power variation under a steady throttle or cruise. The vehicle seems to speed up and slow down with no change in the accelerator pedal.
Preliminary Inspection
  • Refer to Symptoms - Engine Controls.
  • Ensure the driver understands the torque converter clutch (TCC) operation.
  • Ensure the driver understands the A/C compressor operation.
  • Use the scan tool to ensure the vehicle speed sensor (VSS) reading matches the speedometer. This excludes vehicles with electronic transmissions where some variation between VSS and the speedometer is normal.
Fuel System Inspection
  • Test for incorrect fuel pressure.
  • Test for a restricted fuel filter.
  • Test for a contaminated fuel condition.
  • Verify that each injector harness is connected to the correct injector/cylinder according to the firing order.
  • Test the fuel injectors.
  • Test the items that cause an engine to run rich.
  • Test the items that can cause an engine to run lean.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Correct heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the spark plugs are gas, coolant or oil fouled, determine the cause before replacing the spark plugs.
Additional Inspection
  • Inspect the control module grounds for being clean, tight, and in their proper locations.
  • Inspect the generator output voltage. Repair if less than 9 volts or more than 16 volts.
  • Inspect the TCC operation.
  • Inspect the vacuum hoses for splits and kinks.
  • Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom.

Lack Of Power, Sluggishness, Or Sponginess

Inspections
Action
Definition : The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal.
Preliminary Inspection
  • Refer to Symptoms - Engine Controls.
  • Inspect for fuel filters. Aftermarket fuel filters may restrict fuel flow.
  • Compare the vehicle with a similar unit. Ensure the vehicle has an actual problem.
  • Remove the air filter and check for dirt, or for air ducts being plugged or leaking. Repair or replace as necessary.
  • Inspect for a proper transmission operation.
  • Inspect the engine oil level and quality.
Sensor Inspection
  • Inspect the knock sensor (KS) system for excessive spark retard activity with a scan tool.
Fuel System Inspection
  • Inspect for correct fuel system pressure.
  • Inspect for a restricted fuel filter.
  • Inspect for a contaminated fuel condition.
  • Verify that each injector harness is connected to the correct injector/cylinder according to the firing order.
  • Inspect the fuel injectors.
  • Inspect the items that cause an engine to run rich or lean.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Correct heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the apsrk plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs.
Exhaust System Checks
  • Inspect the exhaust system for a possible restriction.
Air Intake System Checks
  • Inspect for an air leak or restriction in the air inlet ducts or the intake manifold.
  • Inspect for a skewed MAP sensor.
Engine Mechanical Check
  • Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom.
  • Inspect the engine for the following conditions:
    • Excessive oil in combustion chamber or leaking valve seals
    • Camshaft timing
    • Excessive carbon buildup in the combustion chambers
    • Improper valve timing
    • Bent pushrods
    • Worn rocker arms
    • Low engine compression
    • Broken or weak valve springs
    • Worn camshaft lobes
  • Inspect the following components for incorrect basic engine parts:
    • Camshafts
    • Cylinder head
    • Pistons, connecting rods, or bearings
Additional Checks
  • Inspect the control module grounds for being clean, tight, and in their proper location.
  • Inspect the torque converter clutch (TCC) operation.
  • Inspect the air conditioning system for proper operation.
  • Inspect the generator output voltage.

Detonation/Spark Knock

Inspections
Action
Definition : A mild to severe ping which usually occurs worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Preliminary Inspection
  • Refer to Symptoms - Engine Controls.
  • Inspect the engine control system grounds for being clean, tight, and in the correct locations. Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms.
  • Verify that the ECM and ECM bracket fasteners are at the correct torque.
  • If the scan tool readings are normal and there are not any engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicle's minimum octane requirements. Road test the vehicle and re-evaluate the vehicle's performance.
Fuel System Inspection
  • Test for incorrect fuel pressure.
  • Test for a restricted fuel filter.
  • Test for a contaminated fuel condition.
  • Test the fuel injectors.
  • Test the items that can cause an engine to run lean.
Sensor/System Inspection
Use a scan tool to monitor the knock sensor (KS) system.
Ignition System Inspection
Ensure that the spark plugs are the correct heat range.
Engine Cooling System Inspection
Test for obvious overheating conditions. Test or inspect for the following conditions:
  • Low engine coolant level
  • Incorrect engine coolant
  • Restricted air flow to the radiator or restricted coolant flow through the radiator
  • Engine coolant leaks
Engine Mechanical Inspection
  • Inspect for the following engine mechanical conditions:
    • Excessive oil in combustion chambers and for leaking valve seals.
    • High cylinder compression.
    • Incorrect camshaft timing.
    • Excessive carbon buildup in the combustion chambers.
  • Inspect the following components for incorrect basic engine parts:
    • Camshafts
    • Cylinder head
    • Pistons, connecting rods or bearings.
Additional Inspection
  • Test the transmission torque converter clutch (TCC) for the correct operation. Applying the TCC too soon can cause the engine to spark knock.

Hesitation, Sag, Stumble

Inspections
Action
Definition : The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move from a stop. If severe enough, the condition may cause the engine to stall.
Preliminary Inspection
Fuel System Inspection
  • Inspect for correct fuel system pressure.
  • Inspect for a restricted fuel filter.
  • Inspect for a contaminated fuel condition.
  • Verify that each injector harness is connected to the correct injector/cylinder according to the firing order.
  • Inspect the fuel injectors.
  • Inspect the items that cause an engine to run rich or lean.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Correct heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the apsrk plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs.
Sensor Inspection
  • Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position.
  • Inspect the MAP sensor for the correct operation.
Engine Cooling System Inspection
Inspect the engine thermostat for the correct operation.
Additional Inspection
  • Review the service bulletins for control module software updates.
  • Inspect the generator output voltage.
  • Inspect for a condition with camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom.

Cuts Out, Misses

Inspections
Action
Definition : A constant jerking that follows the engine speed, usually more pronounced as the engine load increases which is not normally felt above 1500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle, low speed, or hard acceleration for the fuel starvation that can cause the engine to cut-out.
Preliminary Inspection
  • Refer to Symptoms - Engine Controls.
  • Compare the scan tool data at idle with the scan tool data list.
  • Inspect the intake air system for leaks or restrictions.
Sensor Inspection
  • Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool.
Engine Mechanical Check
  • Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom.
  • Inspect the engine for the following conditions:
    • Excessive oil in combustion chamber or leaking valve seals
    • Camshaft timing
    • Excessive carbon buildup in the combustion chambers
    • Improper valve timing
    • Bent pushrods
    • Worn rocker arms
    • Low engine compression
    • Broken or weak valve springs
    • Worn camshaft lobes
  • Inspect the following components for incorrect basic engine parts:
    • Camshafts
    • Cylinder head
    • Pistons, connecting rods, or bearings
Fuel System Inspection
  • Inspect for correct fuel system pressure.
  • Inspect for a restricted fuel filter.
  • Inspect for a contaminated fuel condition.
  • Verify that each injector harness is connected to the correct injector/cylinder according to the firing order.
  • Inspect the fuel injectors.
  • Inspect the items that cause an engine to run rich or lean.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Correct heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the apsrk plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs.
Additional Inspection
  • Inspect the following exhaust system components:
    • The exhaust system for damage
    • The muffler for heat distress or possible internal failure
    • The catalytic converter for restrictions
  • Electro magnetic interference (EMI) on the crankshaft position sensor signal circuits can cause an engine misfire condition. A sudden increase in the engine speed parameter on scan tool, with little change in actual engine speed indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists.

Poor Fuel Economy

Inspections
Action
Definition : Fuel economy, as measured by actual road tests and several tanks of fuel, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by actual road tests.
Preliminary Inspection
  • Refer to Symptoms - Engine Controls.
  • Inspect the air filter for dirt or being plugged.
  • Inspect for an air leak in the charge air cooler.
  • Inspect the air conditioning system for proper operation.
  • Inspect the tires for correct air pressure.
  • Inspect the driving habits of the owner.
  • Are heavy loads being carried?
  • Suggest to the owner to fill the fuel tank and inspect the fuel economy.
Sensor/System Inspection
  • Inspect the air intake system and the crankcase for air leaks.
  • Test the crankcase ventilation system for proper operation.
  • Test for correct calibration of the speedometer. Incorrect tire size or axle ratios can affect speedometer calibration and vehicle mileage.
  • Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool.
Fuel System Inspection
  • Determine the type, quality, and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy.
  • Test for incorrect fuel pressure.
  • Test for a restricted fuel filter.
  • Verify that each injector harness is connected to the correct injector/cylinder according to the firing order.
  • Test the fuel injectors.
  • Inspect for foreign material accumulation in the throttle bore, coking on the throttle valve, or on the throttle shaft. Also inspect for throttle body tampering.
  • Test the items that cause an engine to run rich.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Correct heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the apsrk plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs.
Cooling System Inspection
  • Inspect the engine coolant level.
  • Inspect the engine thermostats for always being open or for the wrong heat range.
Additional Inspection
  • Inspect the transmission for proper operation.
  • Inspect the torque converter clutch (TCC) operation. When the TCC is commanded ON, a scan tool should indicate an RPM drop.
  • Inspect the Service Bulletins for control module software updates.
  • Inspect the brake for proper operation.

Rough, Unstable, Or Incorrect Idle And Stalling

Inspections
Action
Definition : Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary Inspection
  • Refer to Important Preliminary Inspection Before Starting in Symptoms - Engine Controls.
  • Search for bulletins.
  • Inspect the vehicle for factory or aftermarket accessories that may contact the body and chassis. A grounding out condition may simulate a misfire or rough run concern.
  • Inspect the engine control module (ECM) grounds for being clean, tight, and in the proper locations.
  • Remove and inspect the air filter element for dirt or for being restricted. Replace as necessary.
Sensor/System Inspection
  • Test the throttle actuator control (TAC) system.
  • Test the crankcase ventilation system
  • Monitor the knock sensor for excessive spark retard activity with a scan tool.
Fuel System Inspection
  • Inspect for correct fuel system pressure.
  • Inspect for a restricted fuel filter.
  • Inspect for a contaminated fuel condition.
  • Verify that each injector harness is connected to the correct injector/cylinder according to the firing order.
  • Inspect the fuel injectors.
  • Inspect the items that cause an engine to run rich or lean.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Correct heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the apsrk plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs.
Engine Mechanical Inspection
  • Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom.
  • Inspect the engine for the following conditions:
    • Excessive oil in combustion chamber or leaking valve seals
    • Camshaft timing
    • Excessive carbon buildup in the combustion chambers
    • Improper valve timing
    • Bent pushrods
    • Worn rocker arms
    • Low engine compression
    • Broken or weak valve springs
    • Worn camshaft lobes
  • Inspect the following components for incorrect basic engine parts:
    • Camshafts
    • Cylinder head
    • Pistons, connecting rods, or bearings
Additional Inspection
  • Inspect the vacuum hoses for splits and kinks.
  • Inspect the evaporative emission (EVAP) canister purge solenoid for the following:
    • A stuck open condition
    • Charcoal contamination due to a defective EVAP canister.
  • Inspect the following components of the exhaust system for possible restrictions:
    • The exhaust system for damaged or collapsed pipes
    • The exhaust manifold for a collapsed inner wall
    • The mufflers for heat distress or possible internal failure
  • Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM, with little change in actual engine RPM change, indicates that EMI is present. If a problem exists, inspect routing of high voltage components, such as fuel injector wiring, near the sensor circuits.
  • Inspect the park neutral position (PNP) switch circuit.
  • Inspect for faulty engine mounts.
  • Inspect the intake manifold and the exhaust manifold passages for casting flash.

Backfire

Inspections
Action
Definition : Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Preliminary Inspection
  • Refer to Symptoms - Engine Controls.
  • Search for bulletins.
  • Inspect the engine control system grounds for being clean, tight, and in the correct locations. Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms.
  • Verify that the ECM and ECM bracket fasteners are at the correct torque.
Fuel System Inspection
  • Test for incorrect fuel pressure.
  • Test for a restricted fuel filter.
  • Test for a contaminated fuel condition.
  • Inspect that each injector harness is connected to the correct injector/cylinder according to the firing order.
  • Test the fuel injectors.
  • Test the items that can cause an engine to run lean.
Sensor/System Inspection
  • Inspect the air intake system and the crankcase for air leaks.
  • Test the crankcase ventilation system.
  • Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool.
Ignition System Inspection
  • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
  • Inspect the ignition voltage output at the ignition coil. If you suspect an ignition system condition, refer to Electronic Ignition (EI) System Diagnosis.
  • Remove the spark plugs and inspect for the following conditions:
    • Incorrect heat range
    • Wet plugs
    • Cracks
    • Wear
    • Improper gap
    • Burned electrodes
    • Heavy deposits
  • If the spark plugs are gas, coolant or oil fouled, determine the cause before replacing the spark plugs.
Engine Cooling System Inspection
  • Inspect the engine coolant level for being low.
  • Inspect the engine thermostat for the correct operation and heat range.
Engine Mechanical Inspection
  • Inspect for the following engine mechanical conditions:
    • Excessive oil in combustion chamber or leaking valve seals
    • Incorrect cylinder compression
    • Sticking or leaking valves
    • Worn camshaft lobes
    • Camshaft timing
    • Broken valve springs
    • Excessive carbon buildup in the combustion chambers.
  • Inspect the following components for incorrect basic engine parts:
    • Camshafts
    • Cylinder head
    • Pistons, connecting rods, or bearings.
Additional Inspection
  • Inspect the vacuum hoses for splits and kinks.
  • Inspect the intake manifold and the exhaust manifold passages for casting flash.
  • Test the transmission torque converter clutch (TCC). The scan tool should indicate a drop in engine speed when the TCC is commanded ON.
  • Inspect the following exhaust system components:
    • The exhaust system for damage
    • The exhaust manifold for a collapsed inner wall.
    • The mufflers for heat distress or possible internal failure
    • The three-way catalytic converter(s) for restrictions.
  • Electromagnetic interference (EMI) on the crankshaft position (CKP) sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with little change in actual engine speed indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits.
  • Test the park neutral position (PNP) switch circuit.

Dieseling, Run-On

Inspections
Action
Definition : The engine continues to run after the key is turned OFF, but runs very rough. If the engine runs smooth, inspect the ignition switch and the ignition switch adjustment.
Preliminary Inspection
  • Refer to Symptoms - Engine Controls.
  • Search for bulletins.
  • Verify that the engine control module (ECM) and ECM bracket fasteners are at the correct torque.
  • Inspect the engine control system grounds for being clean, tight, and in the correct locations. Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms.
Fuel System Inspection
Test the fuel system for the following conditions:
  • High fuel system pressure
  • Leaking fuel injectors

Malfunction Indicator Lamp (MIL) Inoperative

Circuit Description

Ignition 1 voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

Test Description

Malfunction Indicator Lamp (MIL) Inoperative

Step Action Value(s) Yes No
1
Did you perform the Diagnostic System Check?
-
Go to Step 2
Go to "Diagnostic System Check"
2
Are any other indicators inoperative?
-
Go to Section 9E, Instrumentation/Driver Information
Go to Step 3
3
  1. Turn the ignition OFF.
  2. Disconnect the harness connector from the ECM.
  3. Turn the ignition ON.
  4. Connect a fused jumper wire between the MIL control circuit and ground.
Does the MIL illuminated?
-
Go to Step 8
Go to Step 4
4
Inspect the MIL control circuit for a short to voltage or an open/high resistance.
Did you find and correct the condition?
-
Go to Step 9
Go to Step 5
5
Inspect the ignition 1 voltage supply circuit for a short to ground or an open/high resistance.
Did you find and correct the condition?
-
Go to Step 9
Go to Step 6
6
  1. Inspect the fuse that supplies voltage to the ignition 1 voltage circuit.
  2. If the fuse is open, test all the components connected to the ignition 1 voltage supply circuit.
Did you find and correct the condition?
-
Go to Step 9
Go to Step 7
7
Replace the instrument panel cluster (IPC).
Did you complete the replacement?
-
Go to Step 9
-
8
Replace the ECM.
Did you complete the replacement?
-
Go to Step 9
-
9
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?
-
Go to Step 2
Go to Step 10
10
Check if any additional DTCs are set.
Are there any DTCs that have not been diagnosed?
-
Go to applicable DTC table
System OK

Malfunction Indicator Lamp (MIL) Always On

Circuit Description

Ignition 1 voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

Diagnostic Aids

Malfunction Indicator Lamp (MIL) Always On

Step Action Value(s) Yes No
1
Did you perform the Diagnostic System Check?
-
Go to Step 2
Go to "Diagnostic System Check"
2
  1. Turn the ignition OFF.
  2. Disconnect the harness connector from the ECM.
  3. Turn the ignition ON.
Does the MIL illuminated?
-
Go to Step 3
Go to Step 5
3
Inspect the MIL control circuit for a short to ground.
Did you find and correct the condition?
-
Go to Step 6
Go to Step 4
4
Replace the instrument panel cluster (IPC).
Did you complete the replacement?
-
Go to Step 6
-
5
Replace the ECM.
Did you complete the replacement?
-
Go to Step 6
-
6
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?
-
Go to Step 2
Go to Step 7
7
Check if any additional DTCs are set.
Are there any DTCs that have not been diagnosed?
-
Go to applicable DTC table
System OK


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