VOLVO
ECM-0641 - Reference voltage A. Faulty signal
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
3 modelsC30 (2007–2013), S40 (2004–2013), V50 (2004–2013)
What does this fault code mean?
The ECM keeps watch on the reference voltage that feeds a number of components. If that voltage is not stable, the code is set. The fault may lie in a component's signal wire, which is shorted, or in the control module's own supply of reference voltage. The malfunction indicator lamp may light.
Possible causes
- Component signal wire short-circuited to battery voltage or reference voltage
- Open circuit in the signal wire, or a short to earth in it
- Internal fault in the control module's supply of reference voltage
What you can do
- 1Check the connectors to the components for looseness, contact resistance and oxidation
- 2With the ignition on, check the signal wire to the component for breaks and chafing
- 3Use a multimeter to check that the signal wire has no contact with earth or supply voltage
- 4If the fault remains after these checks, the engine control module is a possible cause; a workshop should decide whether it needs replacing
Symptoms you may notice1
- Malfunction indicator lamp (MIL) lit
General guidance for car owners. Diagnosis on the car can point to a different cause.