| DTC | Affected Circuit |
|---|---|
| P0171 | System Too Lean (Fuel Trim) |
| P0172 | System Too Rich (Fuel Trim) |
DTC IDENTIFICATION
| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. |
Circuit Description
Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term and long-term fuel trim. If both short-term and long-term fuel trim are lean or rich beyond a certain value, MIL will illuminate. DTC P0171 is set when vehicle runs out of fuel.
DTC P0171 is also set when fuel trim is rich beyond a certain preset value after engine has reached normal operating temperature. Possible causes are
- Air intake hose loose.
- Fuel line pressure.
- Injector blockage.
- Heated oxygen sensor.
- Mass Airflow (MAF) sensor.
- Engine Coolant Temperature (ECT) sensor.
- Exhaust System Leak.
DTC P0172 is set when fuel trim is lean beyond a certain value after engine has reached normal operating temperature. Possible causes are
- Fuel line pressure.
- Injector blockage or leak.
- Heated oxygen sensor.
- Mass Airflow (MAF) sensor.
- Engine Coolant Temperature (ECT) sensor.
- Exhaust System Leak.