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Jettadan1, Chevy Technician
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2006 impala check engine light on, ENGINE HOT AC OFF MESSAGE This

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2006 impala check engine light on, ENGINE HOT AC OFF MESSAGE

This message showed up several weeks ago for a few days and then went away. It is now back for 3 days. Temp gauge is stuck on cold and fans runs continuous. What are the potential causes?

Bulletin No.: 06-01-39-006

Date: July 12, 2006


Unable To Change HVAC System Modes (Update HVAC Control Module Software)


2006 Chevrolet Impala, Monte Carlo


with Manual Control HVAC System (RPO CJ3) or Automatic Control HVAC System (RPO C67)


Some customers may comment that they are unable to change the modes in their Heating, Ventilation and Air Conditioning (HVAC) system or that the air is misdirected from the selected mode. The system will reset itself if turned to the defrost mode but the lockup could occur again when moved to other modes.


This condition may be caused by a logic lock-up in the HVAC control module.


Technicians are to reprogram the HVAC control module with an updated software calibration. The new calibration was released beginning with TIS satellite data update version 6.5 which was made available on June 12, 2006. As always, make sure your Tech 2(R) is updated with the latest software version.

It is recommended that the HVAC actuators be recalibrated after the HVAC control module software is updated. Refer to Re-Calibrating Actuators in the HVAC section of SI for more information.

Warranty Information

For vehicles repaired under warranty, use the table.




This say's you can reset it with changing to defrost for a reset. Does this work? Follow up with me












Customer: replied 6 years ago.
The HVAC system is working fine. The engine temp gauge does not work and the engine cooling fans are on full all of the time. Car runs fine but this message keeps appearing every time car is started and the fans run full on.

Can you check your fuses to the sending unit and the temp sending unit? on the radiator

Customer: replied 6 years ago.
Yes I can....Does the temp sender have it's own dedicated fuse? The temp gauge is the only thing not working properly as far as I can tell. I am guessing that when the temp gauge malfunctions the logic for the fans is to go to full on to prevent anuy possible over heat.
It depends on which way the componant fails I figure the temp gauge is not showing do to the blown fuse or a bad temp sending unit.
Customer: replied 6 years ago.
I checked all fan relays (good) and went through the fuse box. Do not see a fuse that seems to be linked to the temp sending unit. I need more specifics on how to check temp sender. I already replaced it with no effect on problem.
I really need to see what codes your impala are throwing. Can you get a scan from autozone and get back with me. I will be on in the morning?
Is yours a lt ls or ltz
Customer: replied 6 years ago.
I have an LT with the 3900 engine.
ok I found some good stuff.
Symptom Related Diagnostic Procedures
Step 1 - Step 17
Step 18

If my answer has helped you please click on accept, but if you are still unsure please click on reply.


Bonuses and positive feedback are alway's appreciated.

Customer: replied 6 years ago.
Thanks this is certainly a good check of the fan systems. I am still puzzled on why the temp gauge is not working. I feel the fan systems are working fine but that they are responding to the fact the temp gauge has no reading.
I feel if you follow this prcedure your temp gauge will come back to life. BUt we can work on that too if this doesnt work.
Jettadan1, Chevy Technician
Category: Chevy
Satisfied Customers: 5064
Experience: Most of our fleet is chevy.
Jettadan1 and other Chevy Specialists are ready to help you
I would really like it if you follow up with me.

Thanks Dan

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