While driving my 02 C5 without the AC on, when the engine gets hot, the cooling fans are not kicking on even at 240 degrees. When I turn the AC on and the passenger compartment is warmer then the temperature setting, the cooling fan will kick on to cool the condenser and will in turn cool the radiator but once I turn the AC off, the fans never come on when the engine is hot. I have replaced all 3 relays for the fans. Does anyone have any other suggestions?
Thanks!

 

Yes, I do have suggestions for you. As you know the relays control the fans and yes, you were correct that there are three of them. Since you are getting them to turn on, that removes the issue of the fan grounds, but FYI, they go through the ground pack on the right forward frame rail adjacent to the hood riser...just in case.
Have you cleaned out the junk in the condensor fins under the front? Plastic bags, paper, bugs and etc? Use a air-wand or a home-made water wand and reverse blow or wash back out towards the front from between the radiator and condensor. This will reward you with a probable good sized pile of small rocks and whatever else.
Past that, is the coolant temperature gauge both analog and digital, working? The coolant temp sensor is more important than a lot of people know and will cause huge problems if its bad, therefore I don't think your's is bad. The fan temps are programmed to come on low-speed around 225 I think and 235 for high-speed but don't hold me to those numbers. Many others in here will know positively. Has your car been to a tuner as the tuner may have altered those temperature settings? Have you checked the coolant level in the engine/surge tank? Has it turned brown? Any leaks? Have you pulled the codes?

 

OK, well after looking at the fans closely, I noticed that only the right (passenger side) fan is working when the air conditioning is on. The left fan is not coming on at all. I wasn’t sure were the ground line is but I did see a plug right next to the hood riser or hinge (passenger side) but is all connected. Here are the answers to your questions:

1. Have you cleaned out the junk in the condenser fins under the front? Plastic bags, paper, bugs and etc? Use an air-wand or a home-made water wand and reverse blow or wash back out towards the front from between the radiator and condenser. Yes, there is nothing blocking the air flow.

2. Is the coolant temperature gauge both analog and digital, working? Yes, both are working.

3. Has your car been to a tuner as the tuner may have altered those temperature settings? I don’t believe it has, it is all stock.

4. Have you checked the coolant level in the engine/surge tank? Has it turned brown? Any leaks? Yes, all is OK.

5. Have you pulled the codes? Yes, all are history codes and they are B2860H, B2283H, B2285H, B2282H, B2284H, C1278H, C1287H and P1518H. None of them have anything to do with this issue from what I can see.


The only other thing I can see is it is a bad fan, a loose connection or a bad ground, can you give me some suggestions as to my next steps?

 

......has a full description of operation and diagnostics. The ground circuit is to the relays and fans are provided by G102. Voltage source can be checked at the underhood electrical center (battery and ign 1). At high speed fan operation the two cooling fans have their own ground paths. That is what I'd check for first, the ground paths from the PCM to the relays and then coolant fans.

Engine coolant over temp occurs when the PCM ( which supplies the fan relays with ground path)detects coolant temps over 256 degrees F and throws a code.

 

On low speed, fans run in series, therefor if one fan motor is bad (or bad connection to that fan), neither will run until high speed is comanded on.

 

Both fans either run low speed all the time when the hvac is on or they run high speed when the system pressure calls for it or the temperature calls for it. Both fan grounds go through the single point at the forward right frame rail as you saw. The right fan is easy to see if its running but the left side is more difficult to detect. Its possible that one might run and the other not if its dead.
Try turning on the hvac to recirc and super cold to see if the fans come on to their high speed mode. If they both come on, did the coolant temp come down? If only one came on, either a bad relay, bad ground through the 3rd relay or a bad fan.

 

Thanks for all your help. I checked the 3rd relay fuse and it looked ok but I replaced it with a new one and it worked. Both fans are working like they should.
Great Advice.