P0138

P0138

Oxygen Sensor After TWC, Bank 1 - Above Limit

Diagnostic conditions
- Exhaust temperature between 250 °C and 750 °C
- Battery voltage between 10 V and 16 V
- 200 seconds after start

Possible cause of fault
- Short circuit to B+ in signal wire
- Oxygen sensor faulty (short circuit to B+)
- DME control module faulty

Affected terminals
DME control module connector A, pin 63, and oxygen sensor connector after TWC, bank 1, pin 2
DME control module connector A, pin 68, and oxygen sensor connector after TWC, bank 1, pin 3
DME control module connector A, pin 69, and oxygen sensor connector after TWC, bank 1, pin 4

Diagnosis/troubleshooting

NOTE: Do not use contact spray on the oxygen sensor plug connections as this may cause irreparable damage to the wiring (contamination of the oxygen sensor via the reference air channel).

NOTE: Do not confuse oxygen sensor ahead of catalytic converter and oxygen sensor behind catalytic converter as this will cause implausible fault entries.

Distinguishing feature of both sensors:

Oxygen sensor in front of catalytic converter (LSU) has a six-pin plug






Oxygen sensor behind catalytic converter (LSF) has a four-pin plug






NOTE: If connector A is disconnected from the DME control module and the ignition is or was switched on, the 'DME Control Module TIMEOUT' fault is recorded in many control modules.

NOTE: If control module connector A was disconnected from the DME in the course of troubleshooting or if the voltage supply was interrupted elsewhere (battery, fuse), the throttle adjusting unit must be adapted.