Circuit Description
WARNING: This page is about a different car, the 2003 Lexus LS 430. However, it is still accessible from the selected car via links, so may be relevant.
Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term and long-term fuel trim.
DTC P0171 or P0174 is set when fuel trim is lean beyond a certain value. Possible causes are:
- Air intake hose loose.
- Fuel injector restricted.
- Faulty Mass Airflow (MAF) sensor.
- Faulty Engine Coolant Temperature (ECT) sensor.
- Improper fuel line pressure.
- Exhaust system leak.
- Open or short in heated oxygen sensor circuit (bank 1 or 2, sensor 1).
- Faulty heated oxygen sensor (bank 1 or 2, sensor 1).
- Faulty ECM.
- PCV hoses.
DTC P0172 or P0175 is set when fuel trim is rich beyond a certain value. Possible causes are:
- Fuel injector restricted or leaking.
- Faulty Mass Airflow (MAF) sensor.
- Faulty Engine Coolant Temperature (ECT) sensor.
- Ignition system malfunction.
- Improper fuel line pressure.
- Exhaust system leak.
- Open or short in heated oxygen sensor circuit (bank 1 or 2, sensor 1).
- Faulty heated oxygen sensor (bank 1 or 2, sensor 1).
- Faulty ECM.