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Eric, Automotive Repair Shop Manager
Category: Buick
Satisfied Customers: 32039
Experience:  20+ yrs. experience as repair shop manager and technician.
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2000 Buick Lesabre, HVAC system. Mode is stuck in vent.

Customer Question

2000 Buick Lesabre, HVAC system. Mode is stuck in vent. Also, when the car is first started, if left in AUTO, the heat never comes on. I have to shut it off and then on, and it will control temp at that point. Just only comes out the vent. How do I get the diagnostic codes? I have checked fuses, all are ok. Trying to check if it is the mode door operator that is bad, or the control unit. What else can I do to check it out>
Submitted: 1 year ago.
Category: Buick
Expert:  Eric replied 1 year ago.


Vehicle » Heating and Air Conditioning » Testing and Inspection » Reading and Clearing Diagnostic Trouble Codes » Displaying & Reading Trouble Codes - HVAC System - Automatic » Without Scan Tool


2000 Buick LeSabre V6-3.8L VIN K

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A Tech II or equivalent scan tool must be used to retrieve Diagnostic Trouble Codes (DTCs) from the PCM memory. DTCs can no longer be retrieved at the data link connector. This also eliminates the PCM function of flashing Code 12. Follow the instructions supplied by the scan tool manufacturer in order to access and read either current and/or history DTCs.

Customer: replied 1 year ago.
I've read multiple sources indicating that pushing the off -temp up at the same time allowed the HVAC controller to go into diagnostic mode. This didn't appear to work. Also read that on-off-vent would allow unit to give diagnostic codes. Note that there hasn't been any engine codes. System Is a a C2J . If no codes are present, what would cause the auto setting not to function until turned off and then on again?
Expert:  Eric replied 1 year ago.


Ok, I gave you from the GM field service manual. The reason that the methods you tried didnt work is because they cant be retreived that way. You have to use a scan tool to retreive them. If you are using a cheap code reader, they dont read body or hvac codes. It needs to be a high end scan tool.

Most of the time what you are describing is a faulty control unit itself, but a high end scan tool is needed to test it to verify it

Customer: replied 1 year ago.
Hmmm, this is from a different post on your site:
To enter the "ACAC Diagnostic System Check," press the "TEMP" up switch and the "OFF" switch on the control panel at the same time. Upon entry, a segment check will be performed and then the graphic display will show pointer number "-00". If the compressor clutch is being requested, the "EXT TEMP" graphics will be displayed. The fan up and fan down switch can be used to increase and decrease the pointer number. The "MIDDLE" switch can be used to change from pointer number -02 to DTC or parameter values for pointers "05-31."
To display HVAC DTCs. select pointer number "-02". and press the "MIDDLE" switch. At this time any current and history trouble codes will be displayed. A failure indicates that the control has detected an open, short to ground or faulty component in that circuit. While that failure is detected, the control will use a default value. When the graphic display is displaying numbers 200 to 299, they appear as numbers 100 through 199 with a "-" in front of them. For example. the value of 200 would be displayed as "-100."
HVAC DTCs can he cleared from H-A/C control by pressing the "OFF" button while in diagnostic pointer number "-02" while the HVAC DTCs are displaying.
To exit the self-diagnostic mode, press the AUTO" switch.It appears from this post that the HVAC codes can be read. From what I understand, the HVAC codes are stored in the control unit, not in the PCM. Which would line up with the above response. Is there different years that retrieval was available via the HVAC controller?
Expert:  Eric replied 1 year ago.


Yes, there are different years, different models and different options on those models that self diagnostic mode was available on.

For your specific year, model and options, there is no self diagnostic mode.

Just a heads up, but trying diagnostic methods or repairs using information from different year, different model, or different options usually winds up in wasting of your time and your money. Sometimes an issue may be universal to any vehicle application, but 99% of the time, the diagnostic methods and repairs are very vehicle specific. Even fault codes have different definitions depending upon year, make, model, engine and transmission configuration