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DTC P0171 or P0172 - FX3

The engine control module (ECM) controls a closed loop air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel delivery based on the signal voltage while in closed loop. A change made to the fuel delivery changes the long and short term fuel trim values. The short term fuel trim values change rapidly in response to the heated oxygen sensor signal voltages. These changes fine tune the engine fuelling. The long term fuel trim values change in response to trends in the short term fuel trim. The long term fuel trim makes coarse adjustments to fueling in order to re-center and restore control to short term fuel trim. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the ECM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition. The fuel trim cells are based on the engine speed and load.

P0171

The average long term fuel trim cell values are greater than 28 percent for 60 counts out of 80.

P0172 (LMT)

The average long term fuel trim cell values are less than -20 percent for 60 counts out of 80.

P0172 (LMU)

The average long term fuel trim cell values are less than -22 percent for 60 counts out of 80.

DTC P0171 and P0172 are Type E DTCs.

DTC P0171 and P0172 are Type E DTCs.

Schematic Reference

Engine Controls Schematics : Siemens ECM - LPG with LCP → Siemens ECM - Gas without FX3 or LCP → Delphi ECM - FX3

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Engine running, verify that other DTCs are not set.

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

2. Ignition ON, verify that the scan tool MAP sensor pressure parameter is within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .

⇒	If not within the specified range, refer to DTC P0130-P0134, P0137, P0138, P013A, P013B, or P0140 : FX3 → Without FX3 .

3. Verify that the scan tool HO2S 1 voltage parameter fluctuates within 200-800 mV.

⇒	If not within the specified range, refer to DTC P0130-P0134, P0137, P0138, P013A, P013B, or P0140 : FX3 → Without FX3 .

4. Engine at normal operating temperature, verify that the scan tool long term fuel trim parameter is between -5 to +5%.

⇒	If not within the specified range, 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 with Special Tool .

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

•	Vacuum leaks at the intake manifold, throttle body, and injector O-rings - P0171.

•	Leaking crankcase ventilation system - P0171.

•	The air intake duct for being collapsed or restricted possibly by a restricted air filter - P0172.

•	Excessive fuel in the crankcase - P0172.

•	Restricted air filter - P0172.

•	The incorrect operation of the evaporative emission control system - P0172.

5. If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical .
6. 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.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.