DTC P0171 Fuel Trim System Lean. Chevrolet S10 Pickup

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 S10 Pickup - 2WD 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 DTC P0171 Fuel Trim System Lean

System Description

In order to provide the best possible combination of driveability, fuel economy, and emission control, a Closed Loop air and fuel metering system is used. While in a Closed Loop, the PCM monitors the oxygen sensor signal voltage. The PCM adjusts fuel delivery based on signal voltage. The long and the short term fuel trim values will indicate a change made to the fuel delivery system. The ideal fuel trim values are around 128 (0 percent). Whenever the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128 (0 to 100 percent). Whenever a rich condition is detected, the fuel trim values will read below 128 (0 to -100 percent), indicating that the PCM is reducing the amount of fuel. Whenever the exhaust emissions reach an excessive level due to a lean condition, a fuel trim DTC is set.

Conditions For Setting The DTC

•	When one or more of the following DTCs are not set P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0300, P0301, P0302, P0303, P0304, P0325, P0335, P0341, P0342, P0401, P0502, P0503, P0506, P0507, P0601, P1133, P1406, P1441.

•	The Fuel Trim Index is above 165.

•	The engine coolant temperature is between 60° C (140° F) and 115° C (239° F).

•	The engine speed is between 750 RPM and 3400 RPM.

•	The vehicle speed is below 70 mph.

•	The TP angle is below 80 %.

•	The MAP is greater than 28 kPa.

•	The BARO is greater than 70 kPa.

•	The IAT sensor is between -25° C(-13° F) and 115° C(239° F).

•	The above conditions are present for greater than 4 seconds.

•	The EVAP canister purge is not occurring.

Action Taken When the DTC Sets

•	The Malfunction Indicator Lamp (MIL) illuminates if the fault is active within the same conditions for 2 out of 80 ignition cycles.

•	The MIL will illuminates after two consecutive ignition cycles in which the diagnostic runs with the fault active.

•	The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information.

•	A history DTC is stored.

Conditions for Clearing the MIL/DTC

•	The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the freeze frame conditions that the DTC failed.

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

•	A scan tool can clear the DTCs.

Diagnostic Aids

•	Check for a poor connection at the PCM. Inspect harness connectors for the following conditions:

-	Backed out terminals

-	Improper mating

-	Broken locks

-	Improperly formed or damaged terminals

-	Poor terminal to wire connection

•	Check for a damaged harness. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving the connectors and wiring harness related to the engine harness. A change in the display will indicate the location of the fault.

•	Check the brake power booster check valve.

Test Description

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

The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.

Visually/physically checking items which may cause a lean condition may determine the cause of the DTC being set.

A vacuum leak can change the Fuel Trim Index and set DTC P0171. This step checks the intake manifold for vacuum leaks.

Contaminants in fuel, such as alcohol or water, can create a lean condition setting a DTC P0171. Checking for these contaminants could identify the fault.

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Are any component related DTCs set?

Go to the Applicable DTC Table

Go to Step 3

Turn the ignition ON leaving the engine off.
Operate the vehicle until the Loop Status indicates Closed.

Is the Fuel Trim Index below the specified value?

165

Go to Step 4

Go to Step 5

Turn the ignition ON leaving the engine OFF.
Review the Freeze Frame data.
Make a note of the parameters.
Operate the vehicle within the Freeze Frame conditions and Conditions For Setting The DTC as noted.

Does the Fuel Trim Index go below the specified value while operating under the specified conditions?

165

Go to Step 16

Go to Step 5

Preliminary checks - visually/physically check the following items:

•	The vacuum hoses for splits, kinks and improper connections.

•	The crankcase ventilation valve for proper installation.

•	The exhaust system for corrosion, leaks, loose or missing hardware.

•	The O2S 1 is installed securely and the pigtail harness is not contacting the exhaust manifold or the engine.

•	The fuel for excessive water, alcohol, or other contaminants.

•	The PCM and sensor grounds are clean, tight and in their proper locations.

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

Go to Step 7

Go to Step 6

Disconnect the MAP sensor electrical connector.
Operate the vehicle in a Closed Loop while monitoring the Fuel Trim Index.

Is the Fuel Trim Index below the specified value?

165

Go to Step 15

Go to Step 9

Repair the fault found in the previous step.
Recheck the Fuel Trim Index while operating the engine.

Is the Fuel Trim Index below the specified value?

165

Go to Step 8

Go to Step 9

Lean condition is not present.

Does a driveability problem exist?

Go to Driveability Symptoms

Go to Step 16

Visually and physically inspect the following items for vacuum leaks:

•	The intake manifold.

•	The injector O-rings.

•	The throttle body.

Repair if any leaks are found.

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

Go to Step 16

Go to Step 10

Start the engine allow it to idle.

Are the IAC counts above the specified value?

Go to Step 11

Go to Step 12

Check the fuel for excessive water, alcohol, or other contaminants.
Correct the contaminated fuel condition if present.

Was the fuel contaminated?

Go to Step 16

Go to Step 13

Refer to DTCs P0506 or P0507 to check the IAC valve performance.
If a problem is found, repair as necessary.

Was a repair necessary?

Go to Step 16

Go to Step 13

Connect a fuel pressure gauge to the fuel system.
Turn the ignition OFF for 10 seconds.
Turn the ignition ON. The fuel pump will run for approximately 2-3 seconds.
It may be necessary to cycle the ignition ON more than once in order to obtain the maximum pressure.
Observe the fuel pressure with the fuel pump running. The pressure should read within the specified value. (When the fuel pump stops, the pressure may vary slightly then hold steady.)

Is the fuel pressure steady? Does it hold?

284-325 kPa

(41-47 psi)

Go to Step 14

Go to Fuel System Pressure Test

Start the engine.
idle the engine until normal operating is reached.
Fuel pressure observed in the above step should drop by the indicated value.

Does the fuel pressure drop by the indicated value?

21-69 kPa (3-10 psi)

Go to Fuel Injector Balance Test and the Fuel Injector Solenoid Coil Test

Go to Fuel System Pressure Test

Replace the MAP Sensor. Refer to Manifold Absolute Pressure Sensor Replacement .

Is the action complete?

Go to Step 16

Using the scan tool, clear the DTCs.
Start the Engine.
Allow the engine to idle until the engine reaches the specified temperature.
Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

90°-95° C

Go to Step 17

Go to Step 2

Check if any additional DTCs are set.

Are any DTCs displayed that have not been diagnosed?

Go to the Applicable DTC Table

System OK