Front heated oxygen sensor (HO2S)

Probe monitoring begins after probe preheating diagnostics are complete. Diagnostic trouble code (DTC) ECM-280A/290A is stored if there is a fault in the front heated oxygen sensor (HO2S) or its wiring causing the signal to deviate from its permitted range.

The control module carries out the following checks of probe control functions.

1. Checking offset (signal too high) 

The control module compares the front and rear adaptation values. A diagnostic trouble code (DTC) is stored when the values deviate by more than 3%.

2. Checking HO2S dynamics (signal too low) 

The control module monitors the aging of the probe by checking its dynamics when switching between lean and rich mixtures. The diagnostic trouble code (DTC) is stored if the control module registers that the probe is operating too slowly.

3. Overheating from the HO2S preheating (signal missing) 

The control module monitors cross-induction from the probe preheating. Diagnostic trouble code (DTC) is stored when cross induction exceeds the permitted value.

4. In the event of a faulty signal, four sections must be checked: 

• A diagnostic trouble code (DTC) is stored if the control module registers that the signal is above 4.8 V for too long.
• A signal is transmitted so that the problem signal is modified if no faults are found in the probe preheating or in the rear probe and the control module registers that the signal from the front probe does not deviate from λ=1. A diagnostic trouble code (DTC) is stored if the signal still does not deviate from λ=1.
• A diagnostic trouble code (DTC) is stored if the control module registers that the signal from the front probe is showing a lean fuel mixture while the signal from the rear probe is showing a rich mixture.
• A diagnostic trouble code (DTC) is stored if the control module registers that the signal from the front probe is showing a rich fuel mixture while the signal from the rear probe is showing a lean mixture.