VOLVO
ECM-231C - Rear heated oxygen sensor (HO2S) aging, bank 2. Signal too high
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 high signal, it concerns the sensor not showing a rich mixture. The engine control module (ECM) changes the fuel-air mixture when the rear sensor on bank 2 does not show a rich mixture, and the code is set if the sensor still does not respond. The usual causes are a leak in the exhaust system or a worn-out sensor.
Possible causes
- Leak in the exhaust system
- Damaged rear oxygen sensor
What you can do
- 1Read the code, clear it and road test to see whether it comes back
- 2Check the exhaust system for leaks, especially at joints and clamps
- 3Do not use rust solvent spray or grease on the sensor connector
- 4Check that the connector to the rear sensor on bank 2 is secure and clean
- 5If no fault is found, have a workshop decide whether a new rear oxygen sensor is needed, since a damaged sensor can cause this fault
Symptoms you may notice1
- Malfunction indicator lamp (MIL) lit
General guidance for car owners. Diagnosis on the car can point to a different cause.