The engine management light came on right after an engine wash. I thought moisture in the EVAP valve wiring. I removed the wiring and dried and cleaned the connector. I reset the error in the ODB2 port. The problem was gone for about 2 weeks when the same error came back. The error states the EVAP is an open circuit. I removed the wiring on the valve and measured it with a Fluke meter, and it read 28 Ohms (from research this is an expected value of a good valve), I compared it with a known working SLK55 without error and it gave the same value of 28 Ohms. I have cleaned the connector and port again and have reset the error.

Does anyone have any other thought on this error or what else I need to check?

cheers
NicW