Q: I have a 2009 Chevrolet Tahoe LT with the 5.3-liter engine. On the instrument panel, I get an error message -- "Engine over Temp—A/C will be shut off" -- while the temp gauge is reading low. Coolant fans will be running, and the engine will not start normally.

When I hold the throttle all the way open, the engine starts, but will not run smoothly. After two or three starts, it runs normally, but the warning stays on. If I disconnect the battery and wait about 15 minutes, the internal error will be reset, and the engine starts and runs normally for weeks or days. I use this truck in Germany and here there's no support for American trucks. Chevy Germany will not or cannot help. Chevy U.S. has not answered me. Hope you can help me out on this.

A: Sorry about your issues with Chevy service overseas. The problem you've described is a somewhat common occurrence on several GM engine applications. Simple as it may sound, the most likely cause is a bad cooling system thermostat. The thermostat becomes partially stuck open, and the powertrain control module (via coolant temperature sensors) sees higher temperatures on the output side of the thermostat within a certain time frame, when it shouldn't. The PCM translates this as a potential "hot" condition, and therefore turns on the coolant fans, shuts off the air-conditioner, and displays the appropriate warning message. No, the engine is not overheating. As a matter of fact, it might take longer to reach normal operating temperature, and heater performance could also be affected. I have not heard too much abou t starting or driveability concerns in this situation. But go ahead and replace the thermostat, then disconnect the battery to reboot the system. That should take care of the problem. If not, it could be a coolant temperature sensor or circuit issue that will require the proper scan tool and technician to diagnose correctly.


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