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George H.
George H., ASE Certified Technician
Category: Car
Satisfied Customers: 19422
Experience:  ASE Master Tech 15+ yrs, AAS Automotive Technology, Factory trained Asian specialist
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no communications with havac system using gm scantool

Customer Question

no communications with havac system using gm scantool
Submitted: 8 years ago.
Category: Car
Expert:  George H. replied 8 years ago.

Hello I will help you with your question,


If you cannot communicate directly with the HVAC control module with a Tech 2 start at the class 2 data list and scan for codes. Post any codes you get here and I will help you work through the diagnosis. You can also ping the modules and watch the right column to see which do not respond.


Is this an auto or manual system?



Customer: replied 8 years ago.
Expert:  George H. replied 8 years ago.

And did you check the class 2 data bus for codes and ping the modules to see which are active on the data bus?



Customer: replied 8 years ago.
i do not have acses to scan tool anymore . i did replace the auto head control in dash. no help
Expert:  George H. replied 8 years ago.

You will need a diagnosis and with the scantool it is possible to see the communication lines. Were there codes?


Could you communicate with the other modules? ABS, PCM BCM etc?


This was a Tech 2 scantool?



Customer: replied 8 years ago.
yes, it was a tech 2 and it would communicate with all other modules
Expert:  George H. replied 8 years ago.

Were any codes set?



Customer: replied 8 years ago.
there were several codes set , the tech did not note them ,i am sending the olds to a dealer soon . thank you
Expert:  George H. replied 8 years ago.

OK this is an advanced diagnosis and for communication issues you have to have a Tech 2 to see the class 2 data buss and how the diagnosis proceeds is dependent on the data and codes that the scantool displays so doing it second hand is almost impossible.


You did the "throw a part at it and see if it sticks" routine so if the control head you installed is OK then the data buss or power and ground is the next issue but the codes that set in the other modules will show what is happening so it is critical to have all the codes and data.


Sorry there is no silver bullet for an issue like this


Let me know if there is anything I can do for you in the future