VOLVO
ECM-257C - 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?
The code is set when the engine control module (ECM) sees that the pump current to the oxygen sensor on bank 2 has stopped. The sensor is then given a default value as its signal, even though the fault is shown as a signal that is too high.
Possible causes
- Oxidation or contact resistance in the connections
- The pump current wire is broken
- The oxygen sensor on bank 2 is damaged
What you can do
- 1Clear the code, road test the car and check whether it comes back
- 2Look at the connector at the lambda sensor: it should be seated firmly and free from oxide. Keep rust solvent spray and grease off the connector
- 3Use a multimeter to check that the pump current wire to the sensor has continuity throughout
- 4Look for breaks and chafing on the wires, especially where they lie close to heat
- 5If the wires are intact but the fault remains, have a workshop check the lambda sensor
Symptoms you may notice1
- Malfunction indicator lamp (MIL) on
General guidance for car owners. Diagnosis on the car can point to a different cause.