Powertrain Controls Diagnosis

DTC P0171 or P0174

Circuit Description

The powertrain control module (PCM) 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 and closed loop. During open loop, the PCM determines fuel delivery based on sensor signals without oxygen sensor input. During closed loop, the oxygen sensor inputs are added and used by the PCM to calculate short and long term fuel trim fuel delivery adjustments. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, this DTC will set.


DTC Descriptors

This diagnostic procedure supports the following DTCs.

- DTC P0171 Fuel Trim System Lean Bank 1

- DTC P0174 Fuel Trim System Lean Bank 2


Conditions for Running the DTC

- DTCs P0101, P0102, P0103, P0107, P0108, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0135, P0137, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0300, P0443, P0496, P0506, P0507, P1121, P1122, P1133, P1134, P1153, or P1154 are not set.

- The engine coolant temperature (ECT) is between 75-115°C (167-239°F).

- The intake air temperature (IAT) is between 20 and +90°C (4-194°F).

- The manifold absolute pressure (MAP) is between 15-1 OS kpa.

- The vehicle speed is less than 132 km/h (82 mph).

- The engine speed is between 400-6,500 RPM.

- The barometric pressure (BARO) is more than 74 kPa.

- The mass airflow (MAF) is between 1-250 g/s.

- The fuel level is more than 10 percent.

- The throttle position (TP) is less than 90 percent.

- DTC P0171 and P0174 run continuously when the above conditions are met.

Conditions for Setting the DTC

The average long term fuel trim cell value is above 24 percent.


Diagnostic Aids

- The system will go lean if an injector is not supplying enough fuel.

- A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel.

- Use a scan tool in order to review the Failure Records. If an intermittent condition is suspected, refer to Intermittent Conditions.Symptom Related Diagnostic Procedures


Test Description

DTC P0171 or P0174 Steps 1-2:

DTC P0171 or P0174 Steps 3-8:

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

5. If conditions were not corrected. refer to Fuel System Diagnosis for a possible fuel problem.Component Tests and General Diagnostics

6. If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be the problem.