DTC P0171, P0172, P0174, or P0175. Chevrolet Caprice WM 2007

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2007 🢒 Caprice WM 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0171, P0172, P0174, or P0175

DTC Descriptor

DTC P0171: Fuel Trim System Too Lean (Bank 1)

DTC P0172: Fuel Trim System Too Rich (Bank 1)

DTC P0174: Fuel Trim System Too Lean (Bank 2)

DTC P0175: Fuel Trim System Too Rich (Bank 2)

Diagnostic Fault Information

Always perform the Diagnostic System Check - Vehicle , prior to using this diagnostic procedure.

Circuit/System Description

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 (CL). During Open Loop the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During CL the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicates a rich condition the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. The FT diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition.

If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets. If the ECM detects an excessively rich condition, DTC P0172 or P0175 sets.

Conditions for Running the DTC

•

DTCs P0030, P0036, P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0117, P0118, P0120, P0121, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0136, P0137, P0138, P0140, P0141, P0201-P0208, P0220, P0300, P0301-P0304, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P1106, P1107, P1114, P1115, P1133, P1516, P2101, P2119, P2120, P2125, P2135, P2138 or P2176 are not set.

•	The engine is in Closed Loop status.

•	The engine coolant temperature (ECT) is between -40 and +150°C (-40 and +302°F).

•	The intake air temperature (IAT) is between -20 and +150°C (-4 and +302°F).

•	The manifold absolute pressure (MAP) is between 18-255 kPa (2.6-37 psi).

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

•	The engine speed is between 400-7,000 RPM.

•	The mass air flow (MAF) is between 1-510 g/s.

•	The barometric pressure (BARO) is more than 70 kPa (10.2 psi).

•	The fuel level is more than 10 percent.

•	This diagnostic runs continuously when the above conditions have been met.

Conditions for Setting the DTC

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

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

DTCs P0171, P0172, P0174 or P0175 are type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0171, P0172, P0174 or P0175 are type B DTCs.

Reference Information

Electrical Information Reference

•	Circuit Testing

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Emission System Information Reference

•	Evaporative Emissions Hose Routing Diagram.

•	Crankcase Ventilation System Inspection/Diagnosis.

Engine Mechanical Information Reference

•	Symptoms - Engine Mechanical.

•	Symptoms - Engine Exhaust.

Fuel System Information Reference

Fuel System Diagnosis.

Scan Tool Reference

Control Module References

Circuit/System Verification

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

•	Verify that other DTCs are not set.

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

•	Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.

⇒	If the value does not vary from approximately 40 mV to approximately 900 mV, refer to DTC P0131, P0132, P0137, P0138, P0151, P0152, P0157, P0158, P2A01, or P2A04 or DTC P0133, P0134, P0140, P0153, P0154, P0160, P1133, or P1153.

Important: EVAP purge activation may cause the FT to be momentarily outside the normal range.

•	The normal Short Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.

•	The Long Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.

Circuit/System Testing

P0171 or P0174

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The reading should be between 0-19 percent.

⇒	If not within the specified range, inspect for the following:

•	Ignition ON, engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure.

Refer to DTC P0106 if the MAP sensor does not indicate the correct barometric pressure.

•	With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2-6 g/s at idle.

Refer to DTC P0101 or P1101 or DTC P0102 or P0103 if the MAF sensor parameter is not within 2-6 g/s at idle.

•	Vacuum hoses for splits, kinks and incorrect connections.

•	Insufficient fuel in the tank.

•	Low fuel pressure.

•	Fuel contamination.

•	Malfunctioning fuel injectors.

•	Missing, loose or leaking exhaust components from the HO2S forward.

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

•	The air induction system and the air intake ducts for leaks or for a missing air filter element.

•	A cracked EVAP canister.

•	Evaporative pipes obstructed or leaking.

•	The crankcase ventilation system for leaks.

•	The HO2S for incorrect installation and for electrical wires or connectors that may have contacted the exhaust system.

•	The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit.

•	Malfunctioning engine components.

P0172 or P0175

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The reading should be between -19 and 0 percent.

⇒	If not within the specified range, inspect for the following:

•	With the engine idling and the transmission in the Park or Neutral position, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor parameter should be between 19-45 kPa. Refer to DTC P0106 if the MAP sensor parameter is not between 19-45 kPa.

•	With the engine idling, observe the mass air flow (MAF) sensor parameter. The MAF sensor parameter should be within 2-6 g/s at idle. Refer to DTC P0101 or P1101 or DTC P0102 or P0103 if the MAF sensor parameter is not within 2-6 g/s at idle.

•	Vacuum hoses for splits, kinks and incorrect connections.

•	The air intake duct for being collapsed or restricted.

•	The air filter for being dirty or restricted.

•	Objects blocking the throttle body.

•	Excessive fuel in the crankcase due to leaking fuel injectors.

•	The evaporative emissions control system for incorrect operation.

•	Excessive fuel pressure.

•	Malfunctioning fuel injectors.

•	Fuel contamination.

•	The HO2S for incorrect installation and for electrical wires or connectors that may have contacted the exhaust system.

•	The HO2S signal circuit shorted to voltage.

Repair Instructions

•	Air Cleaner Assembly Replacement.

•	Air Cleaner Element Replacement.

•	Evaporative Emission Canister Replacement.

•	Evaporative Emission Canister Purge Solenoid Valve Replacement.

•	Evaporative Emission Hoses/Pipes Replacement - Engine.

•	Fuel Hose/Pipes Replacement - Chassis.

•	Fuel Injector Replacement.

•	Primary Fuel Tank Module Replacement.

•	Fuel System Cleaning.

•	Fuel Tank Draining.

•	Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 and Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 , Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

•	Manifold Absolute Pressure Sensor Replacement.

•	Mass Airflow Sensor/Intake Air Temperature Sensor Replacement.

•	Throttle Body Assembly Replacement.

•	Engine Control Module Replacement for engine control module replacement, setup and programming.

Repair Verification

Important:

•	After repairs use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.

•	In order to make sure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the conditions for running and setting DTC P0420 and verify that DTC P0420 runs and passes.

Install any components or connectors that have been removed or replaced during diagnosis.
Perform any adjustment, programming or setup procedures that are required when a component or module is removed or replaced.
Ignition ON, engine OFF.

Important: DO NOT clear codes with the engine running. The codes may reset in the same ignition cycle.

Clear the DTCs.
Ignition OFF for 60 seconds.
Start the engine.
Duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets, or another DTC is present, refer to the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.