DTC P0171 or P0172. Pontiac Vibe

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2009 🢒 Vibe - FWD 🢒 Engine 🢒 Engine Controls and Fuel - 2.4L (LAX) 🢒 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: Fuel Trim System Lean

DTC P0172: Fuel Trim System Rich

In order to provide the best possible combination of driveability, fuel economy, and emission control, the powertrain control module (PCM) uses a Closed Loop air/fuel metering system. The PCM monitors the HO2S signal voltage and when in Closed Loop adjusts fuel delivery based on the HO2S signal voltage. Changes in fuel delivery will be indicated by the long term and the short term fuel trim values that are displayed on the scan tool. The ideal fuel trim value is around 0 percent. The PCM will add fuel when the heated oxygen sensor signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0 percent. The PCM will reduce the amount of fuel delivered when a rich condition is indicated by the HO2S. Fuel trim values below 0 percent indicate a reduction in fuel. A fuel trim DTC can be set when exhaust emissions reach excessive levels because of a lean or rich condition.

HO2S Indication	Short Term FT Action	Long Term FT Action	Short Term FT Response
Lean Condition	Quick Increase of 1% or More	Slow Increase of 1% or More	Return to 0%
Desired Condition	Stays Near 0%	Stays at Learned +/- Value	Stays Near 0%
Rich Condition	Quick Decrease of -1% or Less	Slow Decrease of -1% or Less	Return to 0%

Conditions for Running the DTC

•	DTC P0010, P0011, P0012, P0031, P0032, P0100, P0101, P0102, P0103, P0115, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0220, P0222, P0223, P0335, P0339, P0340, P0341, P0351, P0352, P0353, P0354, P0500, P2135 are not set.

•	The engine coolant temperature (ECT) is greater than 70°C (158°F).

•	The engine is running at steady speed.

•	The engine is operating in Closed Loop.

•	DTC P0171 and P0172 run continuously once the above conditions are met.

Conditions for Setting the DTC

P0171

The average fuel trim value, which is short term fuel trim plus long term fuel trim, is greater than 35 percent for greater than 9 seconds.

P0172

The average fuel trim value, which is short term fuel trim plus long term fuel trim, is greater than -35 percent for greater than 9 seconds.

•	A lean condition during a high fuel demand situation due to a fuel pump that does not deliver enough fuel, a plugged fuel filter, or a restricted fuel pipe can set a DTC P0171.

•	Check for a contaminated oxygen sensor. Silicone and other contaminants can cause the oxygen sensor to provide false exhaust oxygen content readings. If contamination is found, determine the cause and correct the condition before replacing the HO2S.

•	Inspect the HO2S 1 for water intrusion into the wiring harness and the sensor housing. Water can create a short to voltage in the HO2S signal circuit causing a false rich indication.

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

Ignition ON, 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.

Engine idling at normal operating temperatures, observe the scan tool mass airflow (MAF) sensor parameter. The reading should be between 1.5-5.0 g/s.

⇒	If the MAF sensor parameter is not within the range specified, refer to DTC P0101.

Engine running at normal operating temperature, observe the scan tool Long Term FT parameter. The reading should be between -20 to +20 percent.

⇒	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 operating pressure is incorrect--Refer to Fuel System Diagnosis.

•	The fuel injectors are operating lean or rich. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F).

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

•	Vacuum leaks at the intake manifold, manifold fittings, or throttle body - P0171

•	Faulty crankcase ventilation system--Refer to Crankcase Ventilation System Inspection/Diagnosis.

•	A collapsed or restricted air intake duct and a restricted or dirty air filter - P0172

•	Excessive fuel in the crankcase - P0172

•	The incorrect operation of the evaporative emission control system--Refer to Evaporative Emission Control System Diagnosis.

If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical.
Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.