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Dave Nova
Dave Nova, GMC Technician
Category: GM
Satisfied Customers: 19451
Experience:  ASE Master Certification. GM World Class Certification
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I have an 06 Impala, read out on dash says "engine hot a/c

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I have an 06 Impala, read out on dash says "engine hot a/c off" the temp gauge drops to cold and rpms go up. The car is not hot, this will come on when I first start it, I don't beleive that it is the thermosat. Do you have any information on this issue?
Hello and thank you for trusting me with your question. My name is XXXXX XXXXX I will do my best to help you with your GMC problem.

First verify that the cooling sytstem is full and that the engine reaches normal operating temperature after warmed up. If cooling level is low, top off and repair any leaks found. The coolant crossover gaskets are prone to leaking on the 3.5 and 3.9 liter engine.

If the coolant level is okay but the engine does not reach normal operating temperature then the thermostat will need to be replaced.

If the coolant level is okay and the engine does reach normal operating temperature then the PCM (computer) should be updated. GM has released an updated calibration to deal with a false P0128 code. If this code is setting, you will have the symptoms you described.
Customer: replied 4 years ago.

The coolant levels are fine and there are no leaks. The check engine light has never come on. If a false code was happening would the check engine light come on? And, I ask the tech at the dealership about this and he had no idea what calibration i was talking about.

Some codes do not turn on the check engine light on. Typically if the "engine hot/ a/c off " message is showing and the engine is not overheating then you will have a code P0128 code stored. This code will set if the engine does not reach normal temperature, meaning a bad thermostat or could be a computer calibration issue. I have included a copy of the GM technical bulletin below for you. You can reference this bulletin when talking to the dealership tech about the new calibration.

Bulletin No.: 08-06-04-026

Date: April 17, 2008

Intermittent MIL/Check Engine Light On, DTC P0128 Set (Reprogram PCM)

2006 Chevrolet Impala, Monte Carlo

with 3.5L Engine (VINs K, N - RPOs LZE, LZ4)


Some customers may comment that the check engine light illuminates intermittently. Upon inspection, technicians may find DTC P0128 set.


Verify that the cooling system is filled to the proper level and using a Tech 2(R), verify that the thermostat is opening at the proper temperature. If everything is functioning properly, reprogram the PCM with a new service calibration using the TIS2WEB Service Programming System (SPS) application. As always, make sure your Tech 2(R) is updated with the latest software version.
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