VOLVO
ECM-233C - Rear heated oxygen sensor (HO2S), 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?
The engine control module (ECM) controls the heating of the rear oxygen sensor on bank 2. The code is set when the signal is too high while heating is active. The signal wire may have touched a supply voltage, or the sensor may be damaged.
Possible causes
- Signal wire short-circuited to supply voltage
- Damaged oxygen sensor
What you can do
- 1Read and clear the code, then road test to see whether it returns
- 2Look for chafing and pinched wiring on the signal wire to the bank 2 sensor
- 3Check that the sensor connector has not taken in moisture or corrosion
- 4If you have a diagnostic tool: read the sensor signal in live data while the engine runs and see whether it sits too high
- 5If the fault remains, have a workshop decide whether the sensor should be replaced
Symptoms you may notice1
- Malfunction indicator lamp (MIL) lit
What the fault can affect1
- Lambda control is switched off
General guidance for car owners. Diagnosis on the car can point to a different cause.