Oxygen Sensor: Description and Operation

Heated oxygen sensor (HO2S) diagnostic

The front heated oxygen sensor (HO2S) is of the linear type and operates by flow control. Therefore, the signals cannot be measured from the heated oxygen sensor (HO2S) using a multimeter. The rear heated oxygen sensor (HO2S) is of the binary type and functions in the same way as earlier heated oxygen sensors (HO2S).
The engine control module (ECM) checks the heated oxygen sensors (HO2S) when the conditions for the diagnostic have been met.

The following faults can be registered by the control module:
- Electrical faults in the circuits for the heated oxygen sensors (HO2S) and for oxygen sensor preheating.
- Adaption The control module checks that the long-term fuel trim is not higher or lower than the pre-defined values.
- Large difference between the front and rear heated oxygen sensor (HO2S) adaption.The control module checks that the difference between the rear and front heated oxygen sensor (HO2S) adaption is not too large. The fault may be in the front or rear heated oxygen sensor (HO2S) or its wiring.
- Heated oxygen sensor (HO2S) dynamics. The control module checks that the changeover period between rich and lean mixtures is not too long.
- Signals outside their permitted range between the rear and front heated oxygen sensor (HO2S). When the control module registers a rich mixture on the front heated oxygen sensor (HO2S) at the same time as lean mixture is registered on the rear heated oxygen sensor (HO2S)or vice versa.
For further information about diagnostics for the heated oxygen sensor, see "Diagnostic trouble code information" in the diagnostic tool, information manager.