VOLVO
ECM-233B - Rear heated oxygen sensor (HO2S), bank 2. Signal missing
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 by pulsing the current to the sensor's PTC element. The code is set when the signal is too low while heating is switched off. The diagnostic tool shows whether the fault is permanent or intermittent. Typical causes are connection problems and supply faults.
Possible causes
- Contact resistance and oxidation in the connections
- Break in the supply feed that runs from the system relay
- Damaged rear oxygen sensor
What you can do
- 1If you have a diagnostic tool: wait until the diagnostic shows as completed, then read the fault status of the code
- 2With the status reading Fault found, the fault is permanent; with No fault found, it is intermittent and inactive for now
- 3Check that the connector to the rear oxygen sensor on bank 2 is secure and not oxidised
- 4Use a multimeter to check that the supply from the system relay to the sensor has no break
- 5Do not use rust solvent spray or grease in the sensor connector
- 6If 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.