DTC 4-2-5 Rear Heated Oxygen Sensor Regulating

4-1-3 EGR TEMPERATURE SENSOR SIGNAL

Preconditions for DTC
^ The Rear Heated Oxygen Sensor (HO2S) constantly ensures that the Front Heated Oxygen Sensor (HO2S) adjusts the integrator's value in a way which corresponds to the exhaust gas's oxygen content. If the integrator's reading deviates, the Rear HO2S fine tunes the integrator.
^ During engine operation, this adjustment will be both positive and negative. If the adjustment is only positive or negative, the control module will interpret this as damage to the Rear HO2S and DTC 4-2-5 will be set.

Substitute value
^ Fuel trim shut OFF.

Fault reasons
^ Uneven compression.
^ Air leakage in the intake system.
^ Air leakage in the exhaust system.
^ Faulty fuel and residual pressure.
^ Defective rear HO2S.

Fault symptoms
^ May result in impaired performance.