Service Information

Orlando

DTC P0171 or P0172

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0171 00: Fuel Trim System Lean

DTC P0172 00: Fuel Trim System Rich

The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during open loop and closed loop. During open loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During closed loop, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0%. If the HO2S indicates a rich condition, the fuel trim values will be below 0%. The short term fuel trim values change rapidly in response to the HO2S voltage signals. The long term fuel trim makes rough adjustments in order to maintain an optimal air/fuel ratio. A block of memory cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term fuel trim diagnostic is based on an average of cells currently being used. The ECM selects the cells based on engine speed and load. The fuel trim diagnostic will conduct a test to determine if a rich malfunction actually exists or if excessive vapour from the evaporative emission (EVAP) canister is causing a rich condition.

The heating elements inside each heated oxygen sensor (HO2S) heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter closed loop earlier and the control module to calculate the air-to-fuel ratio sooner.

The heated oxygen sensor (HO2S) utilises the following circuits:

•	A signal circuit

•	A low reference circuit

•	An ignition voltage circuit

•	A heater control circuit

Conditions for Running the DTC

•

DTCs P0101 00, P0102 00, P0103 00, P0106 00, P0107 00, P0108 00, P0112 00, P0113 00, P0201 00, P0202 00, P0203 00, P0204 00, P0300 00, P0301 00, P0302 00, P0303 00, P0304 00, P0442 00, P0443 00, P0449 00, P0451 00, P0452 00, P0453 00, P0454 00, P0455 00, P0461 00, P0462 00, P0463 00, P0464 00, P0496 00, P0506 00, and P0507 00 are not set.

•	Where applicable DTCs P2270 00, P2271 00, P2272 00, P2A01 00, are not set.

•	The loop status parameter indicates closed.

•	The fuel trim learn is enabled.

•	The engine coolant temperature (ECT) is between -38 to +1 530°C (-36.4 to +266°F).

•	The intake air temperature (IAT) is between -38 to +150°C (-36.4 to +302°F).

•	The manifold absolute pressure (MAP) is between 15-255 kPa (2-37 PSI).

•	The vehicle speed is less than 134 km/h (83 MPH).

•	The engine speed is between 400-6 000 RPM.

•	The engine airflow is between 1-512 g/s.

•	The fuel level is greater than 10%.

•	The barometric pressure (BARO) is more than 70 kPa.

•	DTCs P0171 00 and P0172 00 run continuously when the above conditions have been met.

Conditions for Setting the DTC

•	The average long term weighted average value is more or less than a calibrated value.

•	The above condition is present for approximately 3 min after the conditions for running the DTC have been met.

Action Taken When the DTC Sets

DTCs P0171 00, P0172 00 are type B DTCs.

Conditions for Clearing the DTC

DTCs P0171 00, P0172 00 are type B DTCs.

Diagnostic Aids

•	On vehicles equipped with a vacuum brake booster, rapid brake pedal cycling may imitate a vacuum leak.

•	The system will become lean if a fuel injector is not supplying enough fuel.

•	A lean condition may be present during high fuel demand due to a fuel pump that does not deliver enough fuel, a plugged fuel filter, or a restricted fuel pipe.

•	The system will become rich if a fuel injector is supplying too much fuel.

•	An exhaust system leak that may not be audible but can cause a DTC to set.

•	A mass air flow (MAF) sensor that is installed incorrectly can set this these DTC's.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Note: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions as illumination of the antilock brake system (ABS), and traction control system indicators.

Engine running, observe the DTC information with a scan tool. Verify that other DTCs are not set.

⇒	If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

Ignition ON, observe the scan tool MAP sensor pressure parameter and compare the reading on the scan tool to the barometric pressure table. Refer to Altitude Versus Barometric Pressure .

⇒	If the MAP sensor pressure is not within the range specified for your altitude.

Engine running, observe the scan tool MAF Sensor parameter. The MAF Sensor parameter should be between 2-6 g/s at idle.

⇒	If the MAF Sensor parameter is not between 2-6 g/s at tick-over, refer to DTC P0101 and DTC P0102 or P0103 .

Engine running, observe the scan tool Throttle Position sensor percentage parameter. The reading should be less than 10%.

⇒	If greater than the specified range, refer toDTC P0121-P0123, P0222, P0223, or P2135 .

Observe the scan tool HO2S Sensor 1 voltage parameter. The reading should fluctuate within 200-800 mV.

⇒	If not within the specified range, refer to DTC P0131, P0132, P0137, or P0138 and DTC P0133, P0134, P0140, P1133, P2270, P2271, or P2A00 .

Engine at normal operating temperature, observe the scan tool Long Term Fuel Trim parameter. The reading should be between -5 to +5%.
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 data.

Circuit/System Testing

Note: You must perform the circuit/system verification before proceeding with circuit/system testing.

Verify none of the following conditions exist:

•	Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•	Splits, kinks, or improper connections at the vacuum hoses

•	The fuel system is operating lean or rich. Refer to Fuel System Diagnosis .

•	The fuel injectors are operating lean or rich. Refer to Fuel Injector Diagnosis : Scan Tool → Special Tool .

•	Leaks in the air induction system between the turbocharger outlet and the throttle body inlet, including the air cooler

•	Missing, restricted, or leaking exhaust components-Refer to Symptoms - Engine Exhaust .

•	Vacuum leaks at the inlet manifold, throttle body, and injector O-rings

•	Leaking crankcase ventilation system

•	The air inlet duct for being collapsed or restricted possibly by a restricted air filter

•	Excessive fuel in the crankcase

•	The incorrect operation of the evaporative emissions control system

If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical .

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.