I have 1999 GMC Jimmy, 2 door, 4x4 with multiple issues that I hope to resolve shortly. Here are the issues:

Heat:
No heat when stopped, blows cold air when I sit at lights....It will blow warm air while driving, and the longer I drive, the warmer it gets. But it is nowhere near the hot air that it used to blow. Could this be a 3-Way Valve / Vacuum problem?

Trans:
Shift Solenoid gone bad. I need to replace the 1-2 shift solenoid. Trans will not shift into OD, I narrowed it down to the solenoid and then had the OBD checked at an emissions inspection (which I failed...) and it verified that there was a shift solenoid malfunction.
I have done a lot of research on the shift solenoid, seems pretty easy to replace, but I am leary about dropping the pan off the trans. Has anyone done this? The other forum I read says that I shouldn't have to remove the frame crossmember, but I think it looks like I WILL need to......

Evap Code:
OBD code for evap malfunction, I checked all the normal things with the gas cap and gas tank fuel level. This comes on all the time, i have had the check engine light on constantly for years......

Any and all help would be appreciated.

Thanks,
Matt

 

Vacuum does not control the temperature door inside the HVAC system. I would say you likely have a clogged core if your temperature gauge reads normal engine temp.

If you have a jack and some jack stands, there is nothing to dropping the pan. You may not have to pull the crossmember, but you won't know until you try it. Even then, you may be able to unbolt the transmission mount from the crossmember and lift the trans up to get enough clearance. That has worked for me in the past anyway.

With any of these things, it would help if you listed the exact code (Pxxxx) that was pulled in the case of the shift solenoid and the EVAP system.

 

Thanks for the info. I will look up the codes I got later. I left the paper in my car at home today.