Engine Hot/AC Turned Off message

[iLikeEggs]

I was driving along on our first cold snap, 21 degrees out. I have the Cold Case aluminum radiator in so it takes longer to get up to operating temp and always runs a bit cooler on the guage. So then I get this message in the DIC. Interesting. Then the both fans start screaming and won't shut off. Then the temp guage goes dead. I get home and check a couple of videos and one recommends replacing the wiring pigtail for the CTS. Makes sense since I have 200k on it. So I pick up a new CTS and pigtail and put it on while it's raining out. Nothing changes. I do some more research and one guy says to pull the 10 Amp fuse in number 12 position, the ECM fuse. Wait 10 seconds and put it back in. What do you know? It worked.
Just put about 100 miles on it since then and normal operation.

 

[RooTBeeRthe1st]

Sounds to me like whoever installed the cold case didn't put a restrictor in the line to the expansion tank.

 

[iLikeEggs]

I have a restrictor (45acp shell casing). I took it out to diagnose another problem which turned out to be a small crack in the overflow tank and also a bad heater hose. Eventually I'll get around to putting it back in.

 

[iLikeEggs]

Update.... Still running strong with no problems. That fuse pull did the trick and only had to be done the one time.

 

[02Z71Raven]

I'm going to ressurect this thread because mine keeps doing it. I had already figured out that fuse 12 would reset it, but its back every time I get back in the truck. it is warmer now than it was in feb and my temp is at 210 when i turn the truck off and the fans are on till i take the key out and then they shut off. Any ideas?

 

[Doubeleive]

I'm going to ressurect this thread because mine keeps doing it. I had already figured out that fuse 12 would reset it, but its back every time I get back in the truck. it is warmer now than it was in feb and my temp is at 210 when i turn the truck off and the fans are on till i take the key out and then they shut off. Any ideas?

Probably the coolant temp sensor, there is probably a ohm test that could be done but I don't think the sensor is very costly anyway.

 

[02Z71Raven]

Probably the coolant temp sensor, there is probably a ohm test that could be done but I don't think the sensor is very costly anyway.

Cheap enough just to replace it yeah. I just don't understand why resetting the ecm would make it work again though.

 

[Doubeleive]

Cheap enough just to replace it yeah. I just don't understand why resetting the ecm would make it work again though.

just clears the data, same as disconnecting the battery for a moment. doesn't fix anything just clears the data, some modules/sensors, etc have to fail 3 times in a row to create a error, same when it is replaced sometimes it has to pass 3 times in a row to pass self testing this is in particular to things like the evap system where it has to do a self test when cold so it can't complete a self test with just 3 key cycles it has to be fully cooled and heated repeatedly. removing the battery terminal erases some of that saved data so it has to start testing again, that's how some peiople get fooled buying a used car sometimes, no cel when they test drive but then 2-3 days later all of a sudden here is a cat code or something unexpected.

 

[02Z71Raven]

Yeah, it came back. This time while I was driving. I'm going to replace the temp sensor and connector. I'll keep yall posted.

 

[Doubeleive]

Yeah, it came back. This time while I was driving. I'm going to replace the temp sensor and connector. I'll keep yall posted.

I wouldn't worry about the connector unless it is visibly fried or has signs of deterioration

 

[02Z71Raven]

I wouldn't worry about the connector unless it is visibly fried or has signs of deterioration

It's not great looking, lol and it's only $5 and I'm a pro at wiring, soldering etc... I often replace them if they make uncomfortable. I'll try just the sensor first though and see what happens. Soldering in that spot isn't going to be easy, so it may be best to do them one at a time anyway, for science.

 

[iLikeEggs]

I wouldn't worry about the connector unless it is visibly fried or has signs of deterioration

Most coolant temp sensors come with a connector and pigtail. It's a good idea to replace the old one as the wires break close to the connector and it's hard to see sometimes. If you're over 100k I would replace the connector.

 

[iLikeEggs]

Might as well revive this thread...
I was driving across town and the AC Engine Hot message came back, fan came on, temp gauge went flat. It's been a while since that happened so I did a search and saw where someone suggested to do a scan and clear the codes. I happened to have my scanner so I plugged it in. It said something about the coolant temp sensor so I cleared it. Sure enough, everything went back to normal. I also or read that this was caused by a minor glitch where the ECM will conflict the outside temp with the coolant temp sensor when it's around 59F out and throw the message on the DIC and crank the fan. Sure enough, it was 59F out. No problems since then. Supposedly it's a common problem across the GMT900 platform.