Heated oxygen sensor (HO2S) diagnostics, overview

Fig 1: Identifying Heated Oxygen Sensor (HO2S)

Courtesy of VOLVO CARS OF NORTH AMERICA.

5 cylinder engines have two heated oxygen sensors (HO2S).

6 cylinder engines have two three-way catalytic converters (TWC) and therefore four heated oxygen sensors (HO2S). The probes work in parallel in two banks. Bank 2 is for cylinders 4 to 6.

The front heated oxygen sensor (HO2S) is a lineal type and functions with current control. Therefore it is possible to measure the signals from the heated oxygen sensor (HO2S) with a multimeter. The rear heated oxygen sensor (HO2S) is a binary type as with earlier heated oxygen sensors (HO2S).

Twin heated oxygen sensor (HO2S) control starts and is active when:

• the front probe has started control,
• the rear probe has reached operating temperature,
• three-way catalytic converter (TWC) temperature has reached +300°C (572°F) (calculated by the control module),
• engine speed (RPM) is >1500 RPM at light load - not at idle speed or under full load.

Twin heated oxygen sensor (HO2S) control is interrupted at fuel shut-off, during misfiring or in the event of a fault in:

• EVAP system,
• catalytic converter,
• heated oxygen sensor (HO2S) heating,
• mass air flow (MAF) sensor.

The control module checks the heated oxygen sensors (HO2S) continually and can register the following types of fault:

The prerequisites for the various checks are summarized below.