DTC P0171 Fuel Trim System Lean. Chevrolet Tracker

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2000 🢒 Tracker - 2WD 🢒 Engine 🢒 Engine Controls - 2.0L 🢒 DTC P0171 Fuel Trim System Lean

Description

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.

Conditions for Running the DTC

•	The barometric pressure (BARO) is more than 75 kPa.

•	The engine coolant temperature (ECT) was between -8°C and +95°C (18°F - 203°F) at engine start up.

•	The intake air temperature (IAT) is between -8°C and +60°C (18°F - 140°F) at engine start up.

Conditions for Setting the DTC

Any of the following conditions are detected while the ECT is less than 110°C (230°F):

•	The short term fuel trim is more than or equal to 15 percent in 128 firing events.

•	The long term fuel trim is more than or equal to 20 percent in 128 firing events.

•	The total fuel trim is more than or equal to 43 percent in 128 firing events.

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 records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC

•	The MIL turns off after 3 consecutively passing cycles without a fault present.

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

•	Perform the scan tool Clear DTC Information function in order to clear the DTC.

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 the 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 .

•	Check for fuel contamination. Small amounts of water can be 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. Refer to Evaporative Emission Control System Diagnosis .

•	A malfunctioning MAF sensor

•	Check for a damaged wiring harness. 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 the 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 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 a faulty electrical connection to the PCM.

If a DTC P0171 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0171 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0171 appears in the Not Ran Since Code Cleared list, the P0171 diagnostic has not yet run. When the DTC P0171 does not appear in the Not Ran Since Code Cleared list, the P0171 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the P0171 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

If a 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 in the diagnostic table.

The Powertrain OBD System Check 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.

This step determines that the fault is present.

Engine control sensors that are found to be out range or fixed, can cause the engine to run lean. Refer to the applicable sensor DTC table for direction in diagnosing any possible sensor error.

This step checks for inadequate fuel delivery from a fuel injector. The fault may be a fuel injector or the fuel injector electrical circuit.

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Start the engine.
Allow the engine to reach a normal operating temperature.
Operate the vehicle until the scan tool indicates Closed Loop.
Observe the Short Term FT parameter on the scan tool.

Is the scan tool display less than the specified value?

15%

Go to Step 3

Go to Step 4

Turn ON the ignition, leaving the engine off.
Perform the scan tool Clear DTC Information function.
Operate the vehicle within the Freeze Frame conditions as noted.
Observe the Total Fuel Trim parameter on the scan tool.

Was the scan tool display less than the specified value while operating the vehicle within the Freeze Frame conditions?

43%

Go to Diagnostic Aids

Go to Step 4

Visually and physically check for any of the following conditions:

•	Any splits, kinks, and improper connections in the vacuum hoses

•	The correct operationPCV valve

•	Any exhaust system leaks near the HO2S

•	The correct operation of the EVAP control system

Repair as necessary.

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

Go to Step 11

Go to Step 5

Start the engine.
Run the engine to normal operating temperatures.
Observe the operation of the following sensors at idle, with a scan tool:

•	The manifold absolute pressure (MAP) 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 Engine 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 11

Go to Step 6

Turn OFF the ignition.
Install a J 34730-1A fuel pressure gauge or an equivalent. Refer to Fuel Pressure Gage Installation and Removal .
Start the engine.
Observe the fuel pressure with the engine idling at normal operating temperatures.

Is the fuel pressure within the specified range?

250 - 300 kPa (36 -43 psi)

Go to Step 7

Go to Fuel System Diagnosis

Check the fuel for excessive water, alcohol, or other contaminants. Refer to .

Was the fuel contaminated?

Go to Step 8

Go to Step 9

Replace any contaminated fuel. Refer to Fuel System Cleaning .

Is the action complete?

Go to Step 11

Check the fuel injectors for any of the following conditions:

•	The discharge of fuel is regular and even. Refer to Fuel Injector Balance Test .

•	The fuel is dispersed in a conical spray pattern.

•	The electrical resistance of the injector coils are all within specifications. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .

Did the fuel injectors pass all the checks?

Go to Diagnostic Aids

Go to Step 10

Replace any faulty fuel injectors. Refer to Fuel Injector and Fuel Rail Replacement .

Is the action complete?

Go to Step 11

Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on the scan tool?

Go to Diagnostic Trouble Code (DTC) List

System OK