VOLVO
ECM-0139 - Rear heated oxygen sensor (HO2S), bank 1. Slow control
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
3 modelsC30 (2007–2013), S40 (2004–2013), V50 (2004–2013)
What does this fault code mean?
The engine control module registers that the rear lambda sensor on bank 1 responds too slowly to changes in the fuel-air mixture and treats this as a fault. The usual reasons are poor contact in the connections or a worn sensor. The fault lights the lamp during driving.
Possible causes
- Contact resistance and oxidation in the connections
- Damaged rear lambda sensor
What you can do
- 1Read, note and clear the code, then road test
- 2Check the rear lambda sensor connector and the wire connection to the control module: is it fully engaged and free from oxidation?
- 3Clean oxidized contacts at the connector and make sure the locking tab engages properly
- 4If you have a diagnostic tool, watch the rear sensor value in live data while pressing and releasing the accelerator. A slow response confirms the fault
- 5If cleaning the contacts makes no difference, have a workshop with diagnostic equipment decide whether the rear lambda sensor should be replaced
Symptoms you may notice1
- Malfunction indicator lamp (MIL) lit
General guidance for car owners. Diagnosis on the car can point to a different cause.