VOLVO
ECM-25BD - Front heated oxygen sensor (HO2S), bank 2. Signal too low
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 low, the difference between the two sensors is what counts. If the front oxygen sensor shows a lean mixture while the rear shows a rich one, the code is set. The fault may sit in either of the two circuits.
Possible causes
- Air leakage in the exhaust system
- The front oxygen sensor indicates an incorrectly rich mixture
- Damaged oxygen sensor
What you can do
- 1Look for air leaks in the exhaust system, especially upstream of the lambda sensors
- 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 lambda sensors
- 4Have a workshop replace the lambda sensors if the fault returns after these checks
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.