Buick Repair Questions? Ask a Mechanic for Answers ASAP
The BCM and PCM command High Speed Fans on under the following conditions:
With that in mind, you could choose not to check A/C refrigerant pressure at this time and just focus on using your scan tool to see whether or not there are any current or pending codes, and to monitor engine temperature to see if it gets up to and over the 230 degree enabling point.
Please let me know what you find and we'll take it from there.
On your opening post you said you could make the fans come on high and low speeds with the scan tool. If that is true, then I don't see how unplugging the BCM would help us in our diagnosis, so let's leave it alone for now.
Now, we know that in this system, the BCM is "the brain" as it determines how long, when and what speed should turn on. The PCM is "the muscle" that engages the cooling fan relays, plus it will control the fans independently if the BCM fails.
What we need to find out is why the fans are not coming on when the coolant temp sensor is telling the BCM that temp is at 248 degrees. In order to do that, we need to confirm the BCM is indeed getting that data, and also whether or not it is commanding the PCM to activate the relays - we could only do that with the help of a Tech-II or equivalent scan tool loaded with the proper software for this MY Rendezvous. Without that tool, all we could do would be guess at the problem - something I don't recommend doing because it can get very expensive very fast.
So, is your current scan tool capable of reading BCM input and ouput PID? If not, can you get one that does?
Hi again. Just checking to see if the information I provided helped you solve your issue. If it did, then kindly accept and rate my answer now. If it didn't, please reply.