Heated Oxygen Sensor (HO2S) Diagnostic

Heated oxygen sensor (HO2S) diagnostic

Heated oxygen sensor (HO2S) diagnostic
Two heated oxygen sensors (HO2S) are used in the Denso engine control module (ECM). The heated oxygen sensors (HO2S) are checked as usual for short-circuits and open-circuits. Diagnostic trouble code (DTC) ECM-2120 (front heated oxygen sensor (HO2S)) or ECM-2200 (rear heated oxygen sensor (HO2S)) will be stored if any of these faults occur. The probe heat elements are also checked. In the event of a fault, diagnostic trouble code (DTC) ECM-2110 (front heated oxygen sensor (HO2S), heating), ECM-2120 (front heated oxygen sensor (HO2S), probe control) or ECM-2210 (rear heated oxygen sensor (HO2S), heating) will be stored. In addition, probe control is also checked. In brief, these checks are carried out as follows.

The front heated oxygen sensor (HO2S)
The front heated oxygen sensor (HO2S), which is a linear type: Two checks where the switch over time between rich-lean and lean rich fuel / air mixture is checked. The diagnostic checks the response time of the front heated oxygen sensor (HO2S) when fuel shut-off is activated and deactivated.
The rich-lean check takes place when the fuel shut-off system is activated, on condition that the sensor current is below a lower limit (indicates rich fuel / air mixture). When the fuel shut-off system is activated, the sensor current usually rises (this indicates a lean fuel / air mixture). The lean-rich check measures the time taken for the sensor current to rise from a lower to an upper limit value. If the time counter exceeds a fault level without the sensor current having reached the upper limit value, the response is considered to be too slow; a fault marker is stored.
The lean-rich check is carried out in a similar way when the fuel shut-off system is deactivated. The difference is that the time taken for the sensor current to fall is measured. Diagnostic trouble code (DTC) ECM-210A (front heated oxygen sensor (HO2S)) is stored in the event of a fault in both of these checks.
In addition, the lambda value is also checked. This value must not deviate significantly from its control value. Diagnostic trouble code (DTC) ECM-210F (front heated oxygen sensor (HO2S)) is stored if the difference is too great.

Rear heated oxygen sensor (HO2S)
The rear heated oxygen sensor (HO2S), which is a binary type, is checked in the following way.
The control module checks the difference between the rear probe voltage maximum and minimum values. This voltage must not exceed 0.5 V. If the difference is greater, the control module takes an initialization value as its starting point. This is a maximum of 0 V and a minimum of 5 V. After this, the rear heated oxygen sensor (HO2S) maximum value must exceed the initialization value (0 V) for the probe voltage by at least 0.6 V and fall below the initialization value (5 V) probe voltage to the minimum value 0.1 V. If these limit values are not reached within approximately 5 minutes and the accumulated and actual probe warming has not reached certain limit values, the control module interprets it as a fault.

Twin probe control starts and is active when
- the front probe has started control
- the rear probe has reached operating temperature

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