This 2003 GMC Envoy came in with the complaint that the a/c will only blow out the defrost and floor. Not through the dash vents. I checked codes and found a code B0263 for a fault with the mode actuator. I first ran into this problem after changing a battery in one of these vehicles last year. Whenever the battery is disconnected the HVAC unit will perform a recalibration of all doors. This causes the door motors to be moved full cycle and the mode door will stick some times. I now hook a jump box to the system before changing the battery in Trailblazers or Envoys to prevent a recalibration from occurring. This way I will not be blamed for a stuck actuator motor.
Anyways to change the actuator motor, first drop the hush panel under the driver’s side of the dash. There are some parts that have to be disconnected from the panel including the turn signal flasher assembly shown in the next picture.
Next, I removed the lower dash knee panel to have a little more room to work.
I had to pull a push pin retainer out at the left side of the duct work in order to remove the driver’s floor vent.
Now, I could finally see the actuator on the side of the heater a/c box.
I removed the actuator and installed the new one. Performed a recalibration with my Tech 2 and put all the panels back in place. A recalibration can be done by disconnecting the battery for at least one minute, reconnect the battery, start the engine and leave the a/c controls alone. I would recommend letting the engine run for at least two minutes, turn the ignition off for at least ten seconds but no more than thirty seconds and then restart the engine so that confirmation of the repair can be done.
I do not recommend connecting the wiring to the actuator until it is installed. They come prepositioned for easier installation.
The notch at the lower edge of the gear is an alignment point. There is a corresponding tab on the door linkage that needs to be lined up with this notch.
To purchase the mode valve actuator, please click here. To see updated information about actuator positions and alignment, please click here.
Check the headlight relay in the underhood fuse box. There are two very black relays that are side by side one is for the low beam headlights and the other is for the cooling fan. When the headlights are not working try swapping the relays. If they start working after swapping the relays buy a new relay and install it. Do not swap them and forget to replace the faulty relay. You will develop overheating and a/c performance problems.
Sparky, I’m the one that you helped with the A/C in my Trailblazer. Another problem came up and I can’t find info on it.
When driving the low beam headlights just go out. The high beams still work fine. After a while the lows may start to work again, or may not. It’s happened a few times in the past and happened last night again. Any suggestions on where to start?
Yes I have read them. I checked the rear air after I posted that the other fix worked for the front vents. It is working perfectly as well.
So this is where I am sitting. I have full control of air/heat in front vents. Also I can control which vents to blow, ie. defrost, floor or a blend. Rear air is working perfectly.
The only problem I have now is the #5 fan speed not working. I think I may quit while I’m ahead and put this off for a while.
We have had this car for nearly a year and been MISERABLE when it was too cold or hot outside.
Thanks again.
Hi Justin,
If you are planning to have some one replace the actuators for you, then you should know that $600 is a little too low and $1200 is way too high. Assuming the shop would be supplying the parts and labor. The problem with the main blower motor will likely be a faulty blower resistor and harness connector. If you have mechanical skills and some tools you can do the work yourself. Have you read the repair posts that I sent the link addresses to?
Thanks for the reply. I have been out of town for about a week.
Got home from work and tried the Actuator Reset. It fixed my first 2problems. THANK YOU! Got an estimate to replace the actuators and check it out. Range was $600 – $1200.
Now I am on to the repairs for #3 & 4 problems. But I can live a while before I have to get those fixed.
THANK YOU AGAIN! I will donating to your site for the help!