VOLVO
ECM-25BC - Front 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?
Although the fault is shown as a signal that is too high, the ECM compares the front and rear oxygen sensors on bank 2. If the front shows a rich mixture while the rear shows a lean one, the code is set. The problem may lie in either of the two sensor circuits.
Possible causes
- Air leakage in the exhaust system
- The front oxygen sensor gives an incorrect signal
- Damaged oxygen sensor
What you can do
- 1Check the exhaust system for air leakage, since a leak can affect the sensor readings
- 2Read the code, clear it and road test the car to see whether it returns
- 3If the exhaust is sealed but the fault remains, have a workshop check the oxygen sensors
- 4If the fault returns after these checks, have a workshop replace the oxygen sensors
Symptoms you may notice1
- Malfunction indicator lamp (MIL) on
What the fault can affect2
- Oxygen sensor control is switched off
- Catalyst diagnostics are switched off
General guidance for car owners. Diagnosis on the car can point to a different cause.