Water Temp Gauge Reads Zero, PCM says XXXF, Turns OFF A/C, Have a 160 Thermo and tune

[jeffstar]

Today on my ritualistic Saturday morning cruise in my Z06 my A/C turned OFF. At first I thought maybe I had hit a button, then I could see the PCM LCD telling me Engine HOT, AC Turned Off (or something like that). The PCM LCD display says xxxF but oil temp is totally normal like 141 degrees.

My car has an 07 with 3001 miles on it a 160 thermo and it has zero coolant leaks. The engine feels cool to the touch at this time. So I unplug the ECT sensor and get the same error/issue. I plug it back in and I get the same error/issue.

This tells me:
1) No ECT sensor signal to the PCM
Which could mean:
Bad sensor
Bad harness

After reading a few different posts on this exact same issue and how this problem solves itself I thought it best to disconnect the battery and let the car sit for 10 minutes, reconnect everything and restart with the ECT plugged in.

This has (for now) solved my issue. I have also used HPTuners (friend has it) to reset the code and the problem instantly goes away.

Question: Has anyone else had this happen before? What resolved this challenge permanently?

My thoughts are:
There is some sort of routine that is taking place with the PCM and thermo and the PCM is being sensitive and thinking the coolant temp sensor is bad?
I could have a bad ECT
I could have an issue with my harness or worse a PCM issue.

[jeffstar]

no dice?

[IDRIVEAG8GT]

Is the oil pressure reading ok? This could be something to do with having a bad 5 volt reference somewhere in the system. I had a similar issue on an 07 Silverado, bad sending unit, and it made everything go haywire. I.E. Limp home mode, fuel tank pressure high, blah blah blah.

[PWRVTEC]

Kinda crazy my 04 Silverado had the same issue today. I had put a new battery and starter in, and after startup, ECT read zero, did a Scan and found there was a code for something coolant related (cannot remeber words it said)

Fixed it by clearing DTC's

[IDRIVEAG8GT]

Kinda crazy my 04 Silverado had the same issue today. I had put a new battery and starter in, and after startup, ECT read zero, did a Scan and found there was a code for something coolant related (cannot remeber words it said)

Fixed it by clearing DTC's

Weird..... If I were you Id shove a stock tune back in it and take it to the dealer..... Unless your Z06 is otherwise, "modded out the ass."

[jeffstar]

Yeah, it's modded so probably not bringing it to GM so they can tell me to screw off

Could be the sensor, I'm popping a new one in Saturday when I do the headers. We'll see.

[IDRIVEAG8GT]

Sounds good. Let us know how it goes.

[jeffstar]

I'm guessing the problem is P0128, which is worried about the Coolant Thermostat. I think there is a logic process where by if Engine Coolant doesn't get to 165 + or so then the computer assumes the Thermostat is busted. Which if the thermostat is stuck open, it can easily become stock closed which would be really bad. I'll update this tread if this DOES NOT fix the problem. If it does I won't update this thread and if you're reading this sometime from now, this fixed my issue.

I disabled P0117 and P0128 error reporting and SES.

[IDRIVEAG8GT]

Depending on the mods performed.... This could be an issue with the PCM's command over the fans. I screwed up the Enable ECT Zone A on a Cadillac STS-V once, and the Engine Coolant gauge read backwards.... And should I have let it run long enough, I probably would've received a code like that.

[wot_denali]

I have the same issue ,since i bought my denali 4 years ago the temp gauge always showing about 212F on highways or even in city summer and winter but the past few days i noticed the temp gauge go lower on highways at night now a days the temp gauge will go to zero getting engine hot ac turned off i pluged the scan tool and found the temp reads 158F which is equal to the gauge so what is going wrong ?

[IDRIVEAG8GT]

That my friend, sounds like a wiring issue.... I know that all the newer crap on the water temp is off by roughly 25 degrees compared to the scanner.... Check the sensor on the drivers side of the block and make sure it's not loose, disconnected, cracked, leaking, etc. If everything is physically well, then you may have a problem in your tune.... Ask DSteck for help. He will most likely know.

[jeffstar]

So yeah, this fixed my issue and I'm really happy about it

[IDRIVEAG8GT]

So yeah, this fixed my issue and I'm really happy about it

Yay! Calls for a celebration!