VOLVO
ECM-257B - 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 that the pump current to the oxygen sensor on bank 2 has stopped, and the sensor signal has been set to a default value. The code is set in that situation.
Possible causes
- Contact resistance or oxidation in the connectors
- Break in the pump current wire to the sensor
- Damaged 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 clean, fully engaged and free from oxide. No rust solvent spray or grease in the connector
- 3Use a multimeter to check that the pump current wire runs unbroken from the sensor to the control module
- 4Inspect the wires to the sensor for chafing and any spots where they may have been pinched
- 5Have a workshop check or replace the lambda sensor if the connector and wiring are intact
Symptoms you may notice1
- Malfunction indicator lamp (MIL) on
General guidance for car owners. Diagnosis on the car can point to a different cause.