I have a 2009 XC90 I bought new from volvo dealership and started giving me electrical problems after the warrantee expired. After spending thousands of dollars the dealership finally let me know it is the CEM problem. I changed the CEM and all problems (headlights, brakelights, airbag message & other error messages) were solved. Later foundout that this is a common issue with volvo which volvo does not disclose and often caused by the high pressure carwash nozzle during vovlo free carwashes, water passes by the windshield wipers to CEM.
