fixerupper88

Well guys turns out was in fact the TCU. I had been watching a few on Ebay while driving by shifting manually and I finally scooped one up for 80 bucks and it works perfect. thanks for all the help. Is there any way to fix up my old one be reprogramming or something or should I just chunk it out?

I sure can. Holy crap that will come is handy. Thank you big time.

I can believe it. I’m more of a part changer myself and I’ve done more electrical trouble shooting following his lead with this than I ever have before. guess ya gotta learn sometime.

Yes I am getting it between those two. Correct me if I’m wrong but isn’t the D1 connection for all the transmission connectivity to the RBT?

Now that you say that I did already try my buddy’s TCU and had the same result. Unless there was some kind of procedure needed other then just plugging it in. How do you check the harness? just find a diagram and check for continuity on each end?

Noooooo! well I guess the search for a good working one begins

Well it does shift while rolling when power is put to the solenoids

OK then I already did this without knowing because I had to drive it for two days while just manually shifting it. first gear works fine then I can't really feel a shift to second but third gear works good and then I can shift it into OD and stay good until I have to slow down eventually and must start over to take off.

Ok thanks, I’ll finish that test tomorrow. Just curious would the solenoids have anything to do with why I’m not able to communicate with the TCM through the diagnostic port?

Well I do hear clicking when I jump both of those pins but how do I verify they are actually working? Have the vehicle running and try to make contact and see if it down shifts and begins to roll?

How do I do that. just cut 2 wires and jump the ground to ground and go to each other solenoid with the positive? I just ohmed them and got 17 on S1, 14 on S2 and 20 on S3

Yep. getting 12v at both of those

Yes I do have continuity between those two points and I am getting 12 volts all the way to the TCM. Also I can read all other system info from the ECU just no transmission

I have replaced the TCM fuse even though the old one tested good. My mechanic said he was getting some power to the unit while in low gear but nothing when in Drive so he suggested replacing Trans position sensor. But no good. I can’t seem to find the FSM diagnostic you posted Eagle. But it does shift good when shifting manually.

I have thrown in the towel on figuring out why the auto tranny on my 88 won’t shift. (The start of the Problem) on two separate occasions when I started the truck and put it into gear it hesitated before downshifting so that I can takeoff. On the third time it refused to shift at all and stayed in high gear as it is now. I own a red brick and after the third time I could no longer communicate with the TCM. Have changed trans range sensor and tried a buddy’s TCM but no improvement. Also have completed the connecter and ground refreshments as well as checked fuses. Is there any way this is a tranny solenoid issue? Any help is greatly appreciated