VOLVO
CEM-1A5C - Communication with the upper electronic module (UEM). Signal missing
System
Central Electronic Module (CEM)
Volvo models this fault code applies to
Applies to the following models:
5 modelsS60 (2001–2009), S80 (1999–2006), V70 (2000–2008), V70 XC / XC70 (2001–2007), XC90 (2003–)
What does this fault code mean?
The central electronic module (CEM) has lost communication with the upper electronic module (UEM) and sets this code. The fault lies in the communication, not in the CEM, so the CEM should not be replaced. The UEM controls, among other things, the roof lights, the power sunroof and remote operation, so those functions may stop working.
Possible causes
- The UEM is not getting power
- The ground wire to the UEM is broken
- Contact resistance in the connections
- Broken CAN wiring to the UEM
- Wrong UEM for this car, for example a used module with different software or hardware
- A common CAN network fault if several communication faults are stored at the same time
What you can do
- 1Check that the UEM has power, for example by switching on a rear reading lamp.
- 2Check the UEM fuse. If it has blown, replace it once. If it blows again, use a multimeter to check the wire after it has no contact with ground.
- 3Check that the connectors to the UEM and the battery connection are seated, not corroded and free of play
- 4Check that the ground wire from the UEM to the body is tight and clean. If the fault remains, use a multimeter to check the wire for breaks
- 5If the airbag warning lamp is lit, do not work on the airbag system yourself. Have a workshop check it. Then clear the code and check the sunroof and remote control.
Symptoms you may notice4
- The remote control does not work
- The power sunroof does not work
- The interior lighting does not work
- The SRS warning lamp may be lit
General guidance for car owners. Diagnosis on the car can point to a different cause.