Heated Oxygen Sensors Diagnostic

Heated Oxygen Sensors Diagnostic

A car with EMS system that meets ULEV2/EURO4 legal demands is fitted with two heated oxygen sensor. The upper sensor is fitted before the TWC (tree way catalyst) and the second in the middle of the TWC. The upper sensor is linear type and the second is a binary type.

There is also a system that meets SULEV legal demands, with three heated oxygen sensors. The upper sensor is fitted before the CCC (Close Coupled Catalytic). The second is situated between stone one and two in the CCC and the third just before the UFC (Under Floor Catalytic). The upper sensor is linear type, the second and the third is binary type. The upper (first) sensor have the following monitoring:
- Slow activation (DTC P0133). The impedance in the element is checked and must drop below a calibrated value a short time after start to check that the sensor gets activated fast enough. Continues monitoring.
- Slow response (DTC P0133). A dither is added to target lambda. The diagnose will then check if the lambda value can follow this square wave. When the sensor is slow enough to give high emission it will be detected as malfunctioning Performed once per driving cycle.
- Heater circuit (DTC P0031, P0032). The sensor heater is continuously monitored. Fault will be detected if circuit is: Open, short to ground or short to battery.
- Sensor circuit (DTC 131, 132). The sensor circuit is continuously monitored. Fault will be detected if sensor circuit is: Open, short to ground or short to battery.

The second sensor have the following monitoring:
- Sensor circuit (DTC P0137, P0138). The sensor working range is checked to detect if sensor have a problem to work in its normal voltage range. Sensor must be able to work in catalyst monitoring area to be judged as normal. Function also monitor if sensor is stuck in range. Continues monitoring.
- Heater circuit (ULEV has DTC P0036- P0038 and SULEV has DTC P0042- P0044). The sensor heater is continuously monitored. Fault will be detected if circuit is: Open, short to ground or short to battery.

The third sensor (SULEV only) have the following monitoring:
- Sensor circuit (DTC P0143, P0144). The sensor working range is checked to detect if sensor have a problem to work in its normal voltage range. Sensor must be able to work in catalyst monitoring area to be judged as normal. Function also monitor if sensor is stuck in range. Continues monitoring.
- Heater circuit (DTC P0042-P0044). The sensor heater is continuously monitored. Fault will be detected if circuit is: Open, short to ground or short to battery.