VOLVO
ECM-256B - 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?
Although the fault is shown as a missing signal, it concerns an implausibly high signal from the oxygen sensor on bank 2 at fuel shut-off, at a time when the calibration current has stopped. Poor contact in the connections or a damaged sensor may be the cause.
Possible causes
- Contact resistance and oxidation in the connectors
- Open circuit in the wire carrying the calibration current
- 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 secure and clean. Do not use rust solvent spray or grease in the connector
- 3Look for breaks and chafing on the wires to the lambda sensor, and check that they do not rest against hot parts
- 4Use a multimeter to check that the wires to the lambda sensor have no open circuit
- 5If the connector and wiring are 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.