Heated Oxygen Sensor (HO2S) Diagnostic

The front heated oxygen sensor (HO2S) is a lineal type and functions with current control. Therefore it is not possible to measure the signals from the heated oxygen sensor (HO2S) using a multimeter. The rear heated oxygen sensor (HO2S) is a binary type as with earlier heated oxygen sensors (HO2S).

The Engine Control Module (ECM) checks the heated oxygen sensors (HO2S) when the conditions for diagnostics have been fulfilled.

The following faults can be registered by the control module:

• Electrical Fault  in the circuits for the heated oxygen sensors (HO2S) and for the heated oxygen sensor (HO2S) preheating
• Adaptation  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) adaptation.  The control module checks that the difference between the rear and front heated oxygen sensor (HO2S) adaptation is not too great. The fault may be in the front or rear heated oxygen sensor (HO2S) or the wiring
• Heated oxygen sensor (HO2S) dynamics.  The control module checks that the changeover period between rich and lean mixtures is not too long.
• Unlikely signals between the front and rear heated oxygen sensors (HO2S).  When the control module registers a rich mixture in the front probe at the same time that a lean mixture is registered in the rear probe or vice versa.