6th Gen ('00-'05): 2003 cooling fans not turning on
Monte Of The Month -- April 2015
Joined: May 2013
Posts: 3,052
From: Brockville Ontario
First thing I would check is the ground under/behind the drivers side headlight, the wires get bad over time and cause a ground issue, mine did this last summer and I replaced the temp sensor, and all 3 relays before I figured it out.
The bcm going bad will cause all sorts of electrical gremlins here is a write up about the bcm going bad
"Problem: I’m experiencing seemingly unrelated electrical problems in the vehicle. This can manifest and power locks that don’t work, parasitic draws that kill your battery while you are away from the car, a radio and instrument cluster that won’t turn off. Problem may be exacerbated by high temperatures
Cause: Bad BCM
Solution: Replace BCM (need to find a shop that has a Tech 2 to program the new BCM to match the vehicle). Do not purchase a used BCM, these are programmable once and cannot be used in another vehicle easily.
Prevention: Avoid jump starting the vehicle as this might kill the BCM"
here is a link to common problems with our cars
https://montecarloforum.com/forum/fwd-tech-guides-95-07-62/list-common-monte-carlo-problems-solutions-30154/
if the ground checks out ok, then I would change the relays, these are located in the fusebox on the passenger inner fender of the car, they are relatively cheap and just pop them out and put the new one in, as it seems the temp sensor is working as your car is not overheating. You said you had checked them, but it could still be an issue and the cheapest way to start repairing the issue, plus it never hurts to replace them as they are probably original.
The bcm going bad will cause all sorts of electrical gremlins here is a write up about the bcm going bad
"Problem: I’m experiencing seemingly unrelated electrical problems in the vehicle. This can manifest and power locks that don’t work, parasitic draws that kill your battery while you are away from the car, a radio and instrument cluster that won’t turn off. Problem may be exacerbated by high temperatures
Cause: Bad BCM
Solution: Replace BCM (need to find a shop that has a Tech 2 to program the new BCM to match the vehicle). Do not purchase a used BCM, these are programmable once and cannot be used in another vehicle easily.
Prevention: Avoid jump starting the vehicle as this might kill the BCM"
here is a link to common problems with our cars
https://montecarloforum.com/forum/fwd-tech-guides-95-07-62/list-common-monte-carlo-problems-solutions-30154/
if the ground checks out ok, then I would change the relays, these are located in the fusebox on the passenger inner fender of the car, they are relatively cheap and just pop them out and put the new one in, as it seems the temp sensor is working as your car is not overheating. You said you had checked them, but it could still be an issue and the cheapest way to start repairing the issue, plus it never hurts to replace them as they are probably original.
Thread Starter
Joined: May 2016
Posts: 38
I appreciate your response. In the fuse box there are 3 fan cont relays. I first took all 3 out, then I took a similar relay and plugged it into the fan cont 1 position, turned the car on and the fan would not come on with the ac still. I also repeated that step for the fan cont 3 position. That also did not work. There are 3 total relays for the fans but only two of them are the same. Do you still think I should purchase new relays? Thanks for your time.
Monte Of The Month -- April 2015
Joined: May 2013
Posts: 3,052
From: Brockville Ontario
Check the ground wire first, as my money is that this is your problem. Replacing them is not a bad thing as they are probably stock but do this after the ground wire. And I would/did only buy one at a time and just switched the two black ones and then purchased the grey one, but that was before I found out about the ground wire lol
Monte Of The Month -- April 2015
Joined: May 2013
Posts: 3,052
From: Brockville Ontario
The wire itself is probably corroded under the plastic sheath, I would cut back a bit from the ground and put a new circle connector (can't think of the name but the circular metal piece that goes under the screw connecting the wire to the frame lol) and replace the ground piece itself and clean the spot where it connects, won't take you long probably 20 minutes tops and then see if that fixes your problem.
Monte Of The Month -- April 2015
Joined: May 2013
Posts: 3,052
From: Brockville Ontario
Anytime, I wouldn't know as much about my car if it wasn't for people helping me in the forum over the years. I hope this solves your problem and if not post and let us know there are a lot of people on here that know all there is to know about these cars and are happy to help
Monte Of The Month -- January 2016
Joined: Feb 2013
Posts: 2,293
From: Pacific NW
Guru.
Aerocupe and Ohara have both offered good advice.
Another possibility is the fan control module. I don't know you can test it, but it communicates with the BCM to tell the fans to turn on. Did check fuses in addition to relays?
I would also say you could be low on refrigerant as the fans won't come on when pressure is low and A/C is turned on, but that wouldn't explain why they don't come on at all w/o unplugging from the ECT sensor.They should come on when the engine reaches operating temperature then turn off again when temperature drops to about180o.
Keep us posted.
Aerocupe and Ohara have both offered good advice.
Another possibility is the fan control module. I don't know you can test it, but it communicates with the BCM to tell the fans to turn on. Did check fuses in addition to relays?
I would also say you could be low on refrigerant as the fans won't come on when pressure is low and A/C is turned on, but that wouldn't explain why they don't come on at all w/o unplugging from the ECT sensor.They should come on when the engine reaches operating temperature then turn off again when temperature drops to about180o.
Keep us posted.
Last edited by plumbob; May 2, 2016 at 08:50 AM.