Ah, the joys of adding computer to systems that never needed computers before. There is a power module in the dash that runs the fan and controls the speed instead of a simple switch. I've never worked on one of these since I left the dealership before they came out, but I've read about the high failure rate of those modules since they have to handle such high current. Typically they fail completely. Since yours works intermittently I would check first to see if any connector terminals are blackened from being overheated or if the connector body is melted.

Answered by caradiodoc (expert)
17,654 answers provided