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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4484
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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I have a 2003 chevy tahoe that the rear temp stays on cold

Customer Question

I have a 2003 chevy tahoe that the rear temp stays on cold all the time . There is a code b0249, we ran down the trouble chart ,and replaced the aux hvac control module . Now we have the temp door actuator moving ,We turn on the key it runs from cold to hot position then back to cold. Check all wires to the actuator 5 volt ok 12 volt ok ground ok continuity to both signal wires ok . Hook up meter check resistance in switch in control panel run low to high ok Check continuity from control panel wire to aux module ok. If we clear the code it stays off till we turn the rear temp switch . Removed the temp actuator check the door moves smooth Any help would be appreciated.
Submitted: 1 year ago.
Category: Chevy
Expert:  Jerry Newton replied 1 year ago.

There is a scan tool recalibration procedure that's necessary when replacing an actuator. What this does is "teach" the controller what the limits of the actuator are. It does this by running the door completely from one stop to the other, then recording the voltage at each stop, and those become the full hot and full cold positions.

If you've done all of the things you listed above, I'd be running the calibration procedure with a Tech 2 to see if this issue goes away.

Customer: replied 1 year ago.
I hook up the tech 2 and ran the calibration on the hvac system, you can hear the front actuators moving to calibrate. The rear actuators do not move. Went to the aux havc system found no calibration.
Expert:  Jerry Newton replied 1 year ago.

I don't have a Tech 2 in front of me, so I can't speak to that.

I can provide this, though: a secondary way to achieve the same thing that doesn't require a scan tool:

Alternate Method (w/o Scan Tool)

  1. Clear all DTCs.
  2. Place the ignition switch to the OFF position.
  3. Install the HVAC actuator.
  4. Connect all previously disconnected components.
  5. Remove the HVAC/ECAS fuse for a minimum of 10 seconds.
  6. Install the HVAC/ECAS fuse.
  7. Start the vehicle.
  8. Wait 40 seconds for the HVAC control module to self-calibrate.
  9. Verify that no DTCs have set as current DTCs.
Customer: replied 1 year ago.
did that way to, still dont work . No dts set , You move the temp knob for rear heat code b0429 comes on
Expert:  Jerry Newton replied 1 year ago.

Since you've moved the temp door full travel, and you can see how far it travels each way, can you tell whether the actuator is moving the door full travel when it cycles like it does?

Customer: replied 1 year ago.
I think i found the problem ,the temp knob when it is moved from cold to hot fast ,sends the code if you move it slow it works . Got a new one on the way ,i will let you know if it repairs the problem.
Expert:  Jerry Newton replied 1 year ago.

Excellent!