Heated Oxygen Sensor (HO2S) Diagnostics, Overview

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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:

ECM-280A / 290A	Fault in the front probe circuit. (ECM-290A is stored for bank 2)
ECM-2A0A / 2B0A	Signal fault in the rear probe circuit.
ECM-2A1A / 2B1A	Rear probe aging.
ECM-2810 / 2910	Fault in the front probe heating circuit.
ECM-2A2A / 2B2A	Fault in the rear probe heating circuit.

The prerequisites for the various checks are summarized below.