VOLVO
ECM-0646 - conditioning (A/C) relay Signal too low
System
Engine Control Module (ECM)
Volvo models this fault code applies to
Applies to the following models:
4 modelsC30 (2007–2013), C70 (2006–2013), S40 (2004–2013), V50 (2004–2013)
Show models by year and engine (12)
- Volvo C30 (2007–2013)2007–2010Engine B4164S3, D4204T only
- Volvo C30 (2007–2013)2011–2012Engine B4164S3 only
- Volvo C70 (2006–2013)2008Engine D4204T only
- Volvo C70 (2006–2013)2009–2010Engine D4204T only · Transmission MMT6, MPS6 only
- Volvo S40 (2004–2013)2004Engine D4204T, D4204T2 only
- Volvo S40 (2004–2013)2005–2006Engine B4164S3, D4204T, D4204T2 only
- Volvo S40 (2004–2013)2007–2010Engine B4164S3, D4204T only
- Volvo S40 (2004–2013)2011–2012Engine B4164S3 only
- Volvo V50 (2004–2013)2004Engine D4204T, D4204T2 only
- Volvo V50 (2004–2013)2005–2006Engine B4164S3, D4204T, D4204T2 only
- Volvo V50 (2004–2013)2007–2010Engine B4164S3, D4204T only
- Volvo V50 (2004–2013)2011–2012Engine B4164S3 only
What does this fault code mean?
The engine control module (ECM) monitors the A/C relay and sets the code when the relay signal comes in below what is expected. The fault can lie in several places: the connections, the signal wire, the supply to the relay or the relay itself. The air conditioning may stop working.
Possible causes
- Contact resistance or oxidation in the connections
- Signal wire open or shorted to earth
- Supply wire to the A/C relay open or shorted to earth
- Damaged A/C relay
What you can do
- 1Check that the air conditioning fuse is intact in the fuse box
- 2With the ignition off, check the connectors at the A/C relay for looseness, contact resistance and oxidation
- 3Use a multimeter to check that the signal wire has no short to earth (the body)
- 4If the fault remains, have a workshop check the supply and the relay and replace them if needed
Symptoms you may notice1
- Air conditioning or temperature control does not work
General guidance for car owners. Diagnosis on the car can point to a different cause.