Expert: John Kingery - 3/16/2008

Question
I have a 98 540i e39 chasis. The ambient temp intermittently drops to -40 and sends the climate control into extreme heat mode. I've replaced the sensor under the front bumper and repaired the wiring at the sensor and checked the wiring up to the firewall. I don't want to replace the climate control unit unless I'm sure that's what it is.
Thanks in advance
David

Answer
I think you're on the right path:  It's the sensor. Not sure the wiring you repaired, but I would next try running separate wire all the way from the sensor to as far back as you can.  If this works, then you can look for the problem wire.  It's most likely the connector on either end, then the wiring, and only last the climate control.  Really doubt it's that.

Good luck