I replaced my coolant temperature sensor due to "engine hot - a/c off" display in message center, also my temp gauge needle was on full cold although the engine was fully warmed up. I also noticed both of my electric fans were running even though the engine was not hot and the A/C was off. First thing I checked was my coolant level and it was full. This message and condition came on again as soon as I restarted the engine after work even though the engine was dead cold, it was 38 degrees out. I had the "message only" for one day, then the message and CEL the second day. I replaced the sensor on the second day. I had to remove the throttle body to gain access to the CTS.

I restarted the car and it ran normally but the eng off message and CEL were still on and the temp gauge still stayed on full cold, also the fans were both still running. I disconnected the battery over night, approx 13 hours. When I reconnected and restarted the car the message was gone, the CEL was off, the fans did not come on and the temperature gauge is working normally.

My problem is the car is idling high now. I drove it 15 miles and at times it was like having the cruise control on at 60 mph on the highway. When I came to a stop it would drop to about 800 in drive at a stoplight but was slow to get down to that rpm. I drove it the 15 miles home again and it was much the same except when I put it in park in the driveway it went to 1500 rpm after searching a bit between 1000 and 2000 rpm.

While I had the throttle body off I found it was quite dirty inside with a black oily, almost greasy buildup especially around the inside of the throttle body throat where the throttle plate sits at idle. I cleaned out the residue and got it all off (clean dry metal) before re-installing the throttle body. I did not do anything else with the throttle body other than spraying and wiping the throat and throttle plate. I was careful while reinstalling the throttle body to seat it flat and tighten it down evenly so I don't think I have a vacuum leak between the throttle body and the intake.

Now I'm wondering if I did something to the throttle body or if the computer is simply trying to relearn the engine after the battery disconnect??? Has anyone else had this experience?

 

Sorry folks, I forgot some basic info. My Monte is a 2006 LT with the 3.5 flex fuel engine.

 

I'd suspect a vacuum leak. I know you were careful around the throttle body but since it didn't have high idle before then that's a good place to start. And check the boot to to air filter box and all seated good.

 

Today was Easter so no work got done. I will double check my work again tomorrow but I'm still curious if the ECM might be relearning the throttle position sensor or if the TPS needs some procedure to reset it after the battery disconnect.

 

Also check to see if you reconnected the throttle cable correctly.

 

I guess the ecm relearn/recalibrate could be possible, but I'd dam near bet on sucking air somewhere around the throttle body or the air filter housing. Make sure all the sensors are plugged back in nice n tight too. Prob just something little that got overlooked.

 

Thx guys for your input:

Aero, I rechecked everything this morning and it's all tight and connected.
Vincenti, my engine has the electric throttle, no cable so that is not an issue.

Now this morning, LOL! After looking under the hood I took it for a ride and although the idle did seem a bit high especially when braking to a stop, almost like fighting the engine a bit, it did seem a lot lower or more normal for the most part and idled around 700-800 in park after warming up. THEN the "eng hot, A/C off" message came back and while the idle was ok the temp gauge went to zero again and the fans came on, no CEL though.

I knew the connector was cracked when I took it off the CTS and put it back but I thought it would be ok. Perhaps a mistake on my part. I bought a new connector and spliced it in, restarted and still have the "eng hot, A/C off" message. I have disconnected the battery again and in a bit I'll reconnect it and see if things go back to normal. I did take extra care to make sure I connected the wires back to the original positions and they are soldered and shrink wrapped for a good clean long lasting connection.

 

Trying to find my thread on "Engine Hot/AC off". Was totally the thermostat. It would not close completely, never got up to temp and the warning came up. Fans run at full tilt, rpms go up etc. CEL code was that for something like coolant temp was out of spec.

Was going to go the temp sensor route but advice here told me to change the 'stat.

UPDATE here's the thread
https://montecarloforum.com/forum/en...-sensor-40462/

 

Baro, thx for the link to your thread. I read it with great interest. Right now my car is running normally with no codes after replacing the connector on the CTS and a battery reset. I'll drive it a little more and see what results. I'm definitely going for the thermostat change if this message returns! I find it amazing that the default setting sends the temp gauge reading to zero but hey, who knows what those engineers were thinking?
One thing I'd like to mention, I have had my engine overheat (due to coolant hose rupture/loss of coolant) and the dash went wild! Chiming constantly, red warning light, engine overheat/shut engine off warning, temp gauge spiked at full hot. This is one reason why I found the "Engine hot AC off" warning so odd. No chimes, no red light and the temp gauge on full cold. Usually my temp needle rises quickly to right on the middle tick mark and never moves. The big difference in the severity of the warnings is a little confusing to me.

 

OK, after reading Barovelli's thread and long thought, I decided that since this was my last day off from the long Easter weekend and facing a long work week ahead I might as well change the thermostat while I have the time. My biggest worry being if the car goes back into the message and fall back mode it might run rich and load up the catalytic convertor, another major expense.

Well...as soon as I got the thermostat out I could see it was bad. The rubber around the close plate was popped off and deformed and obviously impeding the operation of the thermostat. All the other work I did was probably unnecessary based on the condition of the thermostat. I do think the idle problem is a result of the long battery disconnect and I will update in a few days when I see if the idle cures itself or if I need to take further action. I did find a great video on how to change this thermostat and I'll try to include the link here. As this guy states, the real problem is trying to get the system bled after the replacement. I know I had left over coolant and I'll have to monitor the level and overflow bottle for the next week or so.


Hopefully this link works, this video might be a bit longer than you'd like but it really covers the whole replacement correctly. Thanks again folks for responding and as I said, I will report back whether this fixed my problem or not.