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get in my car an hour ago to get ready for a day of consulting, and the check engine light came on as soon as I started the car. Car ran fine, no problems the transmission engine everything normal except I have no AC… In fact, there are no lights on any of the heating and air-conditioning controls. I called OnStar and they were highly unhelpful, the lady read me the code and then read the description and said and I have “and I have no idea what any of that is”… A real confidence builder.
She did say that I just need to get into the dealership within the next seven days so I didn’t get the opinion that it was critical. She said something about serial port data miscomm, but I couldn’t really understand her too well. Can anybody help me shed light on this situation?
UPDATE: i’ve got an appointment for Friday, but I was able to dig out my OBD reader and the only significant code other than this one is use U0164 which is lost communication to the HVAC module… And that figures because I’ve lost my AC or any of the HVAC function, down on the console, all the AC and heat controls work fine from the computer screen.
I’d guess a loose wire connection somewhere, hopefully in the engine bay and not deep inside the dash. Maybe check for a burnt fuse? I haven’t even looked into where the fuse box is on this car. Of course even if you find a burnt fuse the real question would be what caused it to pop.
in the grand scheme sounds like a relatively small issue,
thanks, yeah I think so too. The weather has been real nice recently down here so it’s no problem running around without AC but it’s gonna turn hot pretty quickly here… Lol I guess the good thing is is that it’s not involved with any of the running gear or the drivetrain, I’m gonna check for fuses later today. I think all the fuses that have to do with the AC are the center rear box between the seats so we’ll see if one of those popped…
The HVAC module that is not getting communication , fortunately it’s directly under all the HVAC buttons right on the console so pretty easy to get to, they won’t have to tear the entire dash apart.
when I access any of the HVAC controls via the computer screen, they all work fine, just not the buttons down the console… So I’ve still got AC…
get in my car an hour ago to get ready for a day of consulting, and the check engine light came on as soon as I started the car. Car ran fine, no problems the transmission engine everything normal except I have no AC… In fact, there are no lights on any of the heating and air-conditioning controls. I called OnStar and they were highly unhelpful, the lady read me the code and then read the description and said and I have “and I have no idea what any of that is”… A real confidence builder.
She did say that I just need to get into the dealership within the next seven days so I didn’t get the opinion that it was critical. She said something about serial port data miscomm, but I couldn’t really understand her too well. Can anybody help me shed light on this situation?
UPDATE: i’ve got an appointment for Friday, but I was able to dig out my OBD reader and the only significant code other than this one is use U0164 which is lost communication to the HVAC module… And that figures because I’ve lost my AC or any of the HVAC function, down on the console, all the AC and heat controls work fine from the computer screen.
did they give you an answer on what it was? I just popped the same code right now starting my car
you really gotta take it in because there is another code that may not be showing to you. That is causing this generic POEFF code. This code actually just tells you that there’s something wrong with the network/communications with the modules, and triggers the check engine light. So it means nothing in and of itself.
I got the same CEL code last week and the car was driving fine.
Here is my story on my 2024 C8 Z06 HTC....
At 600 miles I threw a CEL and at 1532 I threw another CEL.
Both CELs resolved on their own after a drive cycle or two.
At 1532 miles I got the P0EFF code on start-up.
I drove directly to the dealer so they could scan it also. After they scanned it they shut the car off.
When I restarted it the CEL was off.
On Thursday I dropped the car off to the service department and I told them I will pick it up Monday or Tuesday.
I will attach the two codes.
They both seem to be nuisance codes.
After the first CEL the dealer reprogrammed the ECM and told me the first code was a known issue.
I am wondering what the deal will be this time.
Again, the car was running fine with both CELs.
I do remote start the car, some people on the forum think that is related, but I always remote started my previous 2023 C8 Z51 HTC and never had a CEL.
That car got Lemon Lawed due to a bad transmission after 6 months and 3700 miles.
help with fault code P0EFF & U0164-HVAC Fault
