DTC P0171. Pontiac Vibe

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2006 🢒 Vibe - FWD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P0171

Circuit Description

The DTC P0171 Fuel Trim System Lean diagnostic monitors the heated oxygen sensor (HO2S) indications of the air/fuel mixture. 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 heated oxygen sensor (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%

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0171 Fuel Trim System Lean

Condition for Running the DTC

•	DTC P0010, P0011, P0012, P0031, P0032, P0100, P0101, P0102, P0103, P0115, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0134, P0335, P0339, P0340, P0341, P0500, P2195, P2196, P2440, P2441, P2444, P2445 are not set.

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

•	The engine is running at steady speed.

•	The engine is operating in Closed Loop.

•	DTC P0171 runs continuously once the above conditions have been met.

Conditions for Setting the DTC

The average fuel trim value is 35 percent or more, for at least 9 seconds. Average fuel trim is short term fuel trim plus long term fuel trim.

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

•	The PCM stores the conditions which were present when the DTC set as Freeze Frame data.

Conditions for Clearing the MIL/DTC

•	The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.

•	A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.

•	A DTC can be cleared by using the scan tool Clear DTC Information function.

Diagnostic Aids

Check for any of the following conditions:

•	Check for vacuum leaks.

•	Check for exhaust leaks.

•	Check for the correct fuel pressure. The fuel system will be lean if fuel pressure is too low. In order to determine the cause of DTC P0171 monitoring the fuel pressure while driving the vehicle at various road speeds may be necessary. Refer to Fuel System Diagnosis .

•	Inspect the wiring harness for damage. If the harness appears to be OK, observe the HO2S 1 display on the scan tool while moving the connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

•	Check for a contaminated oxygen sensor. Silicone and other contaminants can cause the oxygen sensor to provide false lean exhaust readings. If contamination is found, determine the cause of the contamination 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 ground in the HO2S signal circuit, causing a false lean indication.

•	Check the HO2S 1 and the MAF sensor for faulty electrical connections to the PCM.

An intermittent malfunction may be caused by a fault in the HO2S 1 electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

If DTC P0171 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

Visually and physically checking items that may cause a lean condition that may determine the reason that the DTC set.

Engine control sensors that are found to be out range (skewed) or fixed, can cause the engine to run lean. Inspect the performance of the MAF sensor. Inspect for air restrictions and air inlet leaks near the MAF sensor. If the HO2S voltage is fixed low, while the fuel trim is constantly high, check the MAF sensor signal circuit for resistance. High circuit resistance can cause the sensor to read a lower volume of air than actual, resulting in a lean fueling condition. Refer to the applicable sensor DTC table for direction in diagnosing any possible sensor error.

Contaminants in the fuel, such as alcohol or water, can create a lean condition and set DTC P0171. Small amounts of water delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel.

Operating the vehicle in Check Mode enhances the diagnostic capabilities of the PCM. The catalytic converter diagnostic can be monitored on the scan tool under the I/M System Information selection. When the Catalyst test displays a YES status, indicating that the catalytic converter system diagnostic is completed, check for DTC P0420 in the Last Test Failed screen of the scan tool. If there is no DTC P0420 displayed, the catalytic converter diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that the I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

Start the engine.
Operate the vehicle until the loop status indicates Closed Loop.
Observe the Short Term FT parameter display on the scan tool.

Is the Short Term FT parameter displayed on the scan tool less than the specified value?

20%

Go to Diagnostic Aids

Go to Step 3

Visually and physically check for any of the following conditions:

•	Splits, kinks, and improper connections in the vacuum hoses

•	Correct installation of the positive crankcase ventilation (PCV) valve

•	Leaks in the exhaust system

Did any of the above inspections isolate a condition requiring a repair?

Go to Step 10

Go to Step 4

Start the engine.
Run the engine until the engine reaches a normal operating temperature.
Observe the operation of the following sensors at idle, with a scan tool.

•	The mass air flow (MAF) sensor

•	The engine coolant temperature (ECT) sensor

•	The throttle position (TP) sensor

Compare the observed sensor readings with the Typical Scan Tool Data Values located in the engine scan tool data list. Refer to Scan Tool Data List .
Inspect the vehicle for the cause of any errant sensor readings and repair as necessary.

Was a repair necessary?

Go to Step 10

Go to Step 5

Turn OFF the ignition.
Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
Observe the fuel pressure with the engine running at normal operating temperature.

Is the fuel pressure within the specified range?

301-347 kPa (44-50 psi)

Go to Step 6

Go to Fuel System Diagnosis

Check the fuel for excessive water, alcohol, or other contaminants. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Was the fuel contaminated?

Go to Step 7

Go to Step 8

Replace the contaminated fuel.

Is the action complete?

Go to Step 10

Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Special Tool .
Repair or replace as necessary.

Was a repair necessary?

Go to Step 10

Go to Step 9

Is a lean condition still present?

Go to Symptoms - Engine Controls

Go to Step 10

Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 11

Go to Step 2

In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, place the vehicle in Check Mode. Refer to Service Bay Test .
While in check mode, operate the vehicle within the conditions for running and setting DTC P0420 and verify that DTC P0420 runs and passes. Refer to DTC P0420 .

Does DTC P0420 run and pass?

Go to Step 12

Go to DTC P0420

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK