VOLVO
ECM-255B - Front 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 signal from the oxygen sensor on bank 2 is missing, but the fault lies in the engine control module (ECM) itself. It has registered an internal fault in its control of the sensor. If the fault remains, the control module is what needs replacing.
Possible causes
- Damaged engine control module (ECM)
What you can do
- 1Clear the code and road test the car, then check whether the fault comes back
- 2Check that the battery is in good condition and that its terminals are tight
- 3Check the earth points and the connectors to the engine control module for loose contact and oxidation
- 4If the fault remains after these checks, the control module needs replacing; have a workshop do the replacement
Symptoms you may notice1
- Malfunction indicator lamp (MIL) on
General guidance for car owners. Diagnosis on the car can point to a different cause.