Thanks to all of your help from this site, so far I have kept my 1998 GMC Jimmy SLT 4x4 running for two years. Now at 124,000 miles. I have a problem with my blend door yet to be resolved.

I have read just about every thread on the Blend Door issue as my heat has been stuck on now for 2 weeks. I tried to jump the car after the battery died with cables reversed (long weekend). I fixed the cables and jumped the jimmy and ever since then the blend door is stuck on heat.

I have replaced the actuator motor ($140) and tried 3 replacement control units from the junk yard ($75). They all 3 perform exactly the same. I checked the battery and its good but replaced the alternator ($150). I have reset the computer several times and had a local shop check it out ($75) with the same suggestions. Replace actuator motor and dash controls.

My mechanic hooked up his GM computer and tried checking the program as well. ($100) When he sent the command to move the blend door he gets an error 255 (system overload I think). His only suggestion is to start replacing electrical components starting with the body computer.

Any ideas? I have found no burnt wires, no blown fuses and no burnt smell. Something in the system is sending the command to the blend door to stay on heat and I am out of ideas, money and patience. Thanks.