Oxygen Sensor After Catalytic Converter (Cylinders 1 - 3) - Short Circuit to B+

P0138

Oxygen Sensor After Catalytic Converter (Cylinders 1 - 3) - Short Circuit to B+

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

Diagnosis conditions
Diagnostic Trouble Code P0138 is stored by the DME control module when the sensor voltage is continuously above 1 V for more than 0.5 seconds.

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

P0138:

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

Wiring Diagram







Diagnosis Procedure







1 Check wiring harness.

1. Remove all four HO2S connectors.
2. Switch on the ignition.
3. Connect voltmeter at sleeve to pins 3 and 4 of HO2S connector 1 after catalytic converter.
Display: approx. 450 mV

4. Connect voltmeter at sleeve to pin 3 and ground.
Display: approx. 720 mV

If the measurement according to items 3 and 4 does not show the specified values, remove DME control module connector and check wiring for short to B+.

If no short to B+ can be detected, replace DME control module.

2 Check oxygen sensor.

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

1. Remove HO2S connector 1 after catalytic converter.
2. Connect ohmmeter on pin side to pins 1 and 3 of HO2S connector.
Display: Infinity ohm

3. Connect ohmmeter on pin side to pins 2 and 3 of HO2S connector.
Display: Infinity ohm

4. Connect ohmmeter on pin side to pins 1 and 4 of HO2S connector.
Display: Infinity ohm

5. Connect ohmmeter on pin side to pins 2 and 4 of HO2S connector.
Display: Infinity ohm