VOLVO
ECM-25AB - 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 engine control module (ECM) has registered an open circuit in the ground wire to the oxygen sensor on bank 2. The signal is therefore missing, and the fault may lie in the ground wire or in the sensor itself.
Possible causes
- Open circuit in the ground wire
- Damaged front oxygen sensor on bank 2
What you can do
- 1Read the code, clear it and road test the car to see whether it returns
- 2Check that the connector at the lambda sensor is fully engaged and clean, with no oxidation or contact resistance. Do not use rust solvent spray or grease
- 3Use a multimeter to check that the ground wire from the lambda sensor is unbroken all the way
- 4Look for chafed spots and breaks in the ground wire, especially where it is fixed to the body
- 5If the ground wire is intact the sensor may be damaged; have a workshop check it or replace it
Symptoms you may notice1
- Malfunction indicator lamp (MIL) on
General guidance for car owners. Diagnosis on the car can point to a different cause.