 Jim Grant's Tech Tips '00 Pontiac Grand Prix, Head Lights Turn Off With Heater
Q: When I turn on my heater/air conditioner fan the auto head lights go off. Park lights remain on. Can you help me? - Rodney B. A: I suspect that your vehicle’s Body Control Module (aka computer) is getting some bad information or has an internal problem. It is good that the problem is present and can be created on command. The tough part is that it can be difficult to diagnose without a scan tool to talk to the computer. I did some digging and I found that your vehicle’s Body Control Module (BCM) just happens to have the same ground as the fan for the heater and A/C. If the ground is not of good quality it is possible that when the fan is turned on the BCM is getting lost. Computer circuits have to be sound and free of undesigned resistance. The BCM is an electrical whimp. The heater A/C fan is the tough guy. If the ground for the BCM is not the greatest and then you add the high electrical demand of the tough guy heater fan, guess who will lose? The BCM will be cowering in the corner unable to operate correctly. There is just no telling what unexplainable operations will occur from the BCM. I would suggest having your technician chase down ground #G200. A clean and tight connection may get the BCM back on line.
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