2016~2023 Code U0100

[11E20]

Here in Texas we're experiencing record breaking cold. I'm retired and don't drive my 2019 CX-9 FWD that often but needed to go out the other day. The car started fine despite the temps in the teens. I got an warning that my fob battery was low and needed replacement soon (I just recently replaced it) so I shut the car off and got my back up fob from in the house. The car started again but I got another warning about the key fob battery and then a warning about losing connection with the fob and the check engine light came on although the car ran fine. I hooked up a code reader and the U0100, Lost comm with ECM/PCM appeared. I cleared the code and drove without incident. The next day I went out again and experienced no issues or check engine light.

I don't know if it was just the cold effecting the fob battery or if something more significant is going on. Has anyone else seen this? I will visit the dealer if need be as I'm still under warranty but looking for some wisdom from the forum.

 

[Glaucus]

I live in a place with prolonged periods of extreme cold, and haven't experienced THAT code (but I've only had my 2017 CX9 GT AWD since January). I have experienced a different code that's associated with using a block heater, which I doubt you even have.

See the link below. It tries to explain that code. it suggests you clear it and see if it returns. One possible issue might be a dead car battery. Might be a good idea to have that checked. Make sure all your connections are nice and clean. Maybe check your grounds.

U0100 - OBD II Trouble Code: Lost Communication with ECM/PCM

Code U0100 stands for Lost Communication With ECM/PCM. Learn more about causes, symptoms, and diagnostics for code U0100.

repairpal.com

 

[11E20]

Thanks Glaucus; you're right I don't have a block heater. Thanks for the link, I'll check it out. The code hasn't returned since I cleared it and now we're back to much warmer weather. I still plan to take it to the dealer and will see if they have any insight.