P0138

P0138
Short Circuit to Plus at Oxygen Sensor behind Catalytic Converter (Cylinders 1 - 3)

NOTE: This check must be performed on the cold engine.

Function
To diagnose the readiness for operation of the oxygen sensors, the position of the sensor voltage is evaluated (in case of certain faults or conditions, the diagnosis is disabled).

Diagnosis Conditions
Diagnostic Trouble Code P0138 is stored in the Engine Control Module when the sensor voltage is above 1 V for more than 0.1 seconds without interruptions.

Conditions for the diagnosis of the oxygen sensor signals: Sensor heating is active.

NOTE: In case of a short circuit to plus at one oxygen sensor, all the four oxygen sensors will be stored. Furthermore, the fault may cause misfires.





Diagnosis Procedure.

Check wiring harness.
1. Remove all the four oxygen sensor connectors.
2. Switch ignition on.
3. Connect voltmeter at sleeve to pins 3 and 4 of oxygen sensor connector 1 behind catalytic converter. Specified value: approx. 450 mV
4. Connect voltmeter at sleeve to pin 3 and ground.

- Specified value: approx. 720 mV
- If the measurement according to items 3 and 4 does not show the specified values, remove ECM connector and check wires for short circuit to plus.
- If no short circuit to plus can be detected, replace ECM.

Check oxygen sensor.
1. Remove oxygen sensor connector 1 behind catalytic converter.
2. Connect ohmmeter on pin side to pins 1 and 3 of the oxygen sensor connector. Specified value: infinite resistance
3. Connect ohmmeter on pin side to pins 2 and 3 of the oxygen sensor connector. Specified value: infinite resistance
4. Connect ohmmeter on pin side to pins 1 and 4 of the oxygen sensor connector. Specified value: infinite resistance
5. Connect ohmmeter on pin side to pins 2 and 4 of the oxygen sensor connector. Specified value: infinite resistance.