I notice the cooling fans were running wide open on the wifes XT5. Also getting Attention required: steering assist reduced when stated. The coolant temp gauge also doesn't go up. Pulled a P0128 code. I think we have a bad coolant temp sensor. Does anyone know where it's at on this engine? Thanks!!!

I do not know, but I hope someone replies soon because it is nearly impossible to find a solution to this online.

Found it!

Attached Images

File Type: jpg	ECT Sensor (Front Engine).jpg (171.2 KB, 37 views)
File Type: jpg	ECT Sensor (Top Engine).jpg (144.1 KB, 33 views)
File Type: jpg	ECT Sensor Replacement.jpg (142.2 KB, 34 views)

did it work? I just had a mechanic tell me $1900 for a new thermostat....

My 2017 XT5 is experiencing the same issues and code. What was the resolution to the problem? Did you change the temp sensor? Change thermostat? Was it another part at fault? Car is out of warranty and I’m trying to avoid the dealer. Any additional help is greatly appreciated.

Ok, I have had similar issues. I thought my temp sensor was the issues because the dash would quit reading temp. The car dash would then light up steering assistance reduce. The fans then would come on high and the check engine would come on. I had my local mechanic shop replace the sensor ($850.00) It worked for two days. Then the same thing happened again. I hooked up my code reader and cleared the codes. With the code reader still attached i went to the data mode and drove 20 miles. The collant temp never got over 189°F. Then the coolant guage dropped all the way to cold again.
The thermostat is stuck open. So I will bite the bullet and get the Thermostat changed($350 parts $150 Labor. If you have a XT5 built in 2017 and you are not upside-down on the payments trade it in or sell it ro one of you enemies.

If you are under 75,000 miles, this will be covered under the power train warranty.

I know this is an old post, and may be old news by now, but the issue here is the thermostat 100%. I replaced my temp sender twice (once with a parts store part and again with a AC Delco) and it kept giving me issues.
I ordered a GM thermostat from an eBay seller because I couldn’t find a dealer online who had one in stock (May ‘23) for about $150. I replaced it myself and it took about 1.5hrs start to finish. Reused the coolant tube and o-rings and just topped of the fluid.

Hey @AWass - thanks for your post. This sheds a lot of light on the right fix for this!

Does that matter if you’re not the original owner? I’m at 49k miles