1989 GMC Sierra....Electronic Spark Control

Again, more issues/problems with my truck.....ughhhhhhh.

At highway speeds (60-70mph) the "check engine" light will come on. I pulled the codes and it gave me 32-egr issues and 43-esc issues. I think the esc is causing egr issues since I recently replaced egr parts. Also while driving city speeds (30-40mph) the tranny will shift up and down really fast back to back until you get over 40mph. Is all this possibly connected? Where is the esc module on my truck, should I replace it or look further into it?

The ESC Module is square and is mount on a plate above the passenger side valve cover near the throttle body.

I know you replaced EGR and the solenoid but if the code is being set, there could be an issue with EGR passage in the intake manifold or cylinder heads.

//2000CAYukon

So in your opinion, should I replace the ESC module? Is there a way it can be tested to see if its good or not?

I found the problem. The knock sensor mounted next to the starter was disconnected. The wire to the knock sensor had gotten severed.

FYI......The knock sensor wire is DK BLUE and connects to the ESC module mounted next to the TBI.

Not sure about the shifting problem I am having at lower speeds, but I am sure this will help somewhat.

Just thought I would let you guys know that I sold my truck. My new toy is a 1983 Camaro Berlinetta. It's a 5spd with the V6 motor....ughhhhh, I know, but anyway.....I am sure I will be posting many a many questions about it to come, but obviously in a different room/forum. thanx for all your help guys.