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Probe Diagnostics






Probe diagnostics

Heated oxygen sensor (HO2S) diagnostics, overview




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.

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%.

Note! The fault may be in the front or rear heated oxygen sensor (HO2S) circuit.

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 lambda=1. A diagnostic trouble code (DTC) is stored if the signal still does not deviate from lambda=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.

Rear heated oxygen sensor (HO2S), electronic check
Diagnostic trouble code (DTC) ECM-2A0A/2B0A is stored if there is a fault in the rear heated oxygen sensors (HO2S) or its wiring causing the signal to deviate from its permitted value.

Rear heated oxygen sensor (HO2S), aging
The control module checks the rear heated oxygen sensor (HO2S) dynamics. The control module checks that the probe has registered both lean and rich fuel mixtures. If this is the case, a signal is transmitted so that the probe signal is changed. Diagnostic trouble code (DTC) ECM-2A1A / 2B1A is stored if the rear probe has still not registered lean or rich fuel mixture. The diagnostic trouble code (DTC) is also stored if the switch over time from lean to rich fuel mixture is too long.

Front heated oxygen sensor (HO2S), preheating
Checking that the heating circuit begins after dew point has been reached. The control module registers an electrical fault and checks the probe's lambda value. A diagnostic trouble code (DTC) for a faulty signal is stored if the value deviates from 1 within a set time after the control module interprets that heated oxygen sensor (HO2S) preheating is not working.

Preheating, rear heated oxygen sensor (HO2S)
Checking that the heating circuit begins after dew point has been reached. The control module registers electrical faults in the front probe. The control module measures the resistance in the heater element so that the probe temperature (which is continuously compared with a temperature model) can then be calculated. A diagnostic trouble code (DTC) for a faulty signal is stored if the temperature in the probe is lower than a designated value in the temperature model.

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