VOLVO
ECM-231D - Rear heated oxygen sensor (HO2S) aging, bank 2. Signal too low
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
2 modelsS80 (1999–2006), XC90 (2003–)
Show models by year and engine (2)
What does this fault code mean?
Although the code is named for a low signal, it concerns the sensor on bank 2 not showing a lean mixture. At fuel cut-off the sensor should show a lean mixture, and the code is set if it does not, or if the change to lean takes too long. The cause may be a leak in the exhaust system or a damaged sensor.
Possible causes
- Leak in the exhaust system
- Damaged rear oxygen sensor
What you can do
- 1Read and clear the code, then road test with stretches where the engine brakes without throttle
- 2Inspect the exhaust system for leaks, since a leak can stop the sensor responding as it should
- 3Check that the connector to the rear sensor on bank 2 is clean and secure
- 4If you have a diagnostic tool: read the oxygen sensor signal in live data while the engine brakes without throttle and see whether it shows a lean mixture
- 5If no fault is found, have a workshop decide whether a new rear oxygen sensor is needed
Symptoms you may notice1
- Malfunction indicator lamp (MIL) lit
General guidance for car owners. Diagnosis on the car can point to a different cause.