DTC EFI-425

4-2-5 REAR HEATED OXYGEN SENSOR, CONTROL





Trouble Code Conditions
- The rear heated oxygen sensor (HO2S) constantly monitors the front heated oxygen sensor, ensuring that it adjusts the short term fuel trim integrator so that it corresponds to the exhaust gas oxygen content. If the short term fuel trim integrator deviates, the rear heated oxygen sensor will make fine adjustments to it. While the engine is running this adjustment can be both positive and negative. If the adjustment is only positive or negative the engine control module (ECM) interprets it as a damaged rear heated oxygen sensor and EFI-425 is posted.

Substitute value(s)
- Twin heated oxygen sensor fuel trim disabled.

Possible source(s)
- Uneven compression.
- Air leakage in the intake system.
- Air leakage in the exhaust system.
- Faulty fuel and residual pressure.
- Defective rear heated oxygen sensor.

Fault symptom(s)
- None.