Symptoms - Engine Controls
Diagnostic Instructions
Symptoms Description
Symptoms cover conditions that are not covered by DTCs. Certain conditions can cause multiple symptoms. These conditions are listed together under Symptoms Testing. Conditions that may only cause specific symptoms are listed separately under additional symptoms testing.
However, symptoms which affect the internal combustion engine (ICE) of a typical gas powered vehicle may not be noticeable on the Volt ICE. For the Volt ICE, symptoms such as, hesitation, sag, stumble, sluggishness, surging, and even engine stalling, are buffered by the Voltec propulsion system, which is designed to smooth out ICE irregularities. Even when the battery pack is depleted and the ICE is forced to run in order to sustain the charge, the battery pack should still have enough retained power to perform this buffering function. Refer to Hybrid Modes of Operation Description for more information.
Perform the symptoms testing before using the additional symptoms testing.
Symptoms Definition
Backfire: Fuel ignites in the inlet manifold or in the exhaust system, making a loud popping noise.
Cuts Out, Misfires: A steady pulsation or jerking that follows engine speed. The exhaust has a steady spitting sound.
Detonation/Spark Knock: A mild to severe ping which usually gets worse while under load. The engine makes sharp metallic knocks that change with throttle opening.
Dieseling, Run-On: The engine continues to run after the vehicle is turned OFF.
Engine Control Module (ECM) Commanded Reduced Engine Power: The ECM illuminates the Reduced Engine Power lamp and will limit engine power under potential engine damaging or emissions related conditions. A DTC may be not be set.
Fuel Odor: A noticeable smell of unburned fuel.
Hard Start: Engine does not start for a long time. The engine does eventually run, or may start but immediately stall.
Poor Fuel Economy: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.
Poor Fuel Fill Quality: Difficulty when refuelling the vehicle.
Rough, Unstable Idle and/or Stalling: The engine runs unevenly. If severe, the engine or the vehicle may shake and the engine may stall.
Symptoms Verification
Before using the Symptom tables, perform the following inspections
| • | Verify the engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly. |
| • | Verify there are no DTCs stored. |
| • | Verify the scan tool data is within the normal operating range. |
| • | Verify there are no Bulletins available for the current symptom. |
| • | Verify the vehicle tires are correctly inflated and meet original equipment specifications. |
| • | Perform the Visual/Physical Inspection in this section. The visual/physical inspection is extremely important, and can lead to correcting a condition without additional testing. It may also help to reveal the cause of an intermittent condition. |
Identifying Intermittent Conditions
Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movements of a component. Refer to the following for a list of issues that may cause an intermittent condition:
| • | Moisture and water intrusion in connectors, terminals, and components |
| • | Incomplete connector mating |
| • | High circuit or component resistance-High resistance can include any resistance, regardless of the amount, which can interrupt the operation of the component. |
| • | Harness that is too short or tight |
| • | Wire insulation that is chaffed or cut |
| • | High or low ambient temperature |
| • | High or low engine coolant temperature |
| • | High underhood temperature |
| • | Excessive heat in a component or in a circuit due to circuit resistance, poor terminal contact, or high electrical load |
| • | High or low system voltage |
| • | High vehicle load conditions |
| • | Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge |
| • | Incorrect installation of aftermarket, add on accessories |
Visual/Physical Check
| • | Verify that the control module grounds are clean, tight, and correctly located. |
| • | Verify that the vacuum hoses are not split or kinked, and are properly routed and connected. |
| • | Verify that the air filter is clean and free from restrictions. |
| • | Verify that there is no water intrusion in connectors, terminals, and components. |
| • | Inspect the air inlet ducts for the following conditions: |
| • | Inspect for air leaks at the throttle body mounting area, the mass air flow (MAF) sensor and inlet manifold sealing surfaces. |
| • | Inspect the wiring harness for the following conditions: |
| • | Inspect for loose, damaged, unseated, or missing sensors/components. |
| • | Inspect the terminals for corrosion and correct contact. |
Symptoms Testing
Backfire, Cuts-Out, Misses, Detonation/Spark Knock, Dieseling/Run-On, ECM Commanded Reduced Engine Power, Fuel Odor, Hard Start, Poor Fuel Economy, Poor Fuel Fill Quality, or Rough, Unstable Idle and/or Stalling.
| • | Test or inspect the fuel system for the following conditions: |
| • | Test or inspect the ignition system for the following conditions: |
| | Note: Observe the scan tool Cylinder 1-4 Current Misfire Counters and the Ignition Coil Control Circuit Status parameters to help isolate an ignition system condition. |
| - | Secondary ignition system component susceptible to moisture. Wet down the secondary ignition system with water from a spray bottle. This may help locate damaged or deteriorated ignition system components. Look/listen for arcing or misfiring as the water is applied. |
| • | Test or inspect for the following conditions: |
| - | Items that can cause an engine to run lean or rich. Refer to DTC P0171 or P0172 for additional information. |
| - | An intermittent crankshaft position sensor condition. Observe the scan tool Crankshaft Position Resync Counter parameter. The Resync Counter parameter should remain at 0 during all operating conditions, and when moving the related harnesses and connectors between the crankshaft position sensor and the ECM. |
| - | Electromagnetic interference on the reference circuit, which can cause a misfire condition. You can usually detect electromagnetic interference 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 may be an indication that electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists. |
| - | Inspect the heated oxygen sensors (HO2S) for contamination from fuel, silicon, or the incorrect use of RTV sealant. The sensors may have a white powdery coating resulting in a high, but false, signal voltage, which gives a rich exhaust indication. |
| - | A leaking or restricted positive crankcase ventilation system. |
| • | Inspect the exhaust system components for the following: |
| - | Physical damage or possible internal malfunction. |
| - | Restricted 3-way catalysts. |
| • | Inspect the engine cooling system for the following conditions: |
| - | Improperly operating engine coolant thermostat heater. Refer to DTC P0597-P0599 . |
| • | Inspect the engine for the following mechanical failures: |
| - | Excessive oil in the combustion chamber or leaking valve seals |
| - | Incorrect cylinder compression |
| - | Sticking or leaking valves |
| - | Excessive carbon buildup in the combustion chambers. Clean the chambers with top engine cleaner, if necessary. Follow the instructions on the can. |
| • | If the above conditions do not address the symptom, refer to the additional symptoms tests. |
Additional Symptoms Tests
Detonation/Spark Knock
| • | Inspect for excessive carbon buildup in the combustion chambers. Clean the chambers with Top Engine Cleaner, if necessary. Follow the instructions on the can. |
Engine Control Module (ECM) Commanded Reduced Engine Power
Review the scan tool Reduced Engine Power History parameter to determine the reason for the last reduced engine power event.
Fuel Odour
| • | Inspect for a condition with the internal components of the fuel tank assembly. Refer to Fuel System Description . |
Hard Start
| • | Test the engine coolant temperature (ECT) sensor. Compare the ECT sensor value to the inlet air temperature (IAT) sensor value on a cold engine. The ECT and IAT sensor values should be within approximately 3°C (5°F). If the ECT sensor is out of range with the IAT sensor, test the resistance of the ECT sensor. Refer to Temperature Versus Resistance for resistance specifications. Replace the ECT sensor if the resistance is not within specification. If the sensor is within the specification, test the ECT circuits for a high resistance. |
| • | Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Inspection and Cleaning . |
Poor Fuel Economy
| • | Inspect for heavy loads being carried or towed. |
| • | Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Inspection and Cleaning . |
Poor Fuel Fill Quality
| • | Inspect for restricted vent lines |
| • | Inspect for high fuel temperature |
| • | Inspect for a condition with the internal components of the fuel tank assembly |
For more information, refer to the following:
Rough, Unstable Idle and/or Stalling
| • | Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Inspection and Cleaning . |
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