PCM/Trans issue

[Sugmadique]

This truck isn’t my daily so it sits days at a time. I inherited a 99 Cummins with issues and have been working through them. Random no start, replaced cps, problem fixed. Random loss of tach and acceleration, replace apps, problem solved. Then one day I’m driving and the trans goes into limp mode, I don’t have time to deal with it so I park it for a couple weeks. When I go to pull it in i can manually put it in first but if I just use drive it’s still in limp mode. The alternator is also not charging now. For whatever reason neither of my scan tools (mx808, Verdict) can communicate with the transmission. However I can see the ECM and I have code p1693. I check power and ground to the PCM and both are good so I assume it’s a bad PCM due to the alternator not charging (tested good) and no communication with transmission. Spent $400 on a junkyard PCM but nothing changed. Bypassed the PCM voltage regulator and put in a stand alone and the alternator is now charging. I pulled the output shaft speed sensor and it was covered in the magic glitter so I replaced it.  Transmission is now shifting properly through 3rd but I still don’t have O/D or tcc lockup. I tried the trick where you put a 1k ohm resistor in line on the white plug pin #1 violet wire. Now the “No O/D” light is on and the switch will not turn it off, and the “trans temp” light is also on. Any advice? 

[pepsi71ocean]

Check the transmission relay under the hood in the PDC. Swap it with another one of the same size. 

 

It sounds like the relay went bad. 

Edited October 20, 2019 by pepsi71ocean

[Evan]

Why not just put a jumper in where relay goes?

[dripley]

You could do either. But if your horn works just swap them and see what happens. Quick and simple.

[pepsi71ocean]

8 hours ago, Evan said:

Why not just put a jumper in where relay goes?

 

Because if the relay has failed it's better to know. That relay controls the power for both the transmission and the alternator. It's the feed that runs the solenoids inside the transmission for lock up.

[JAG1]

Do you get the 400 bucks back from the junkyard? Or is it a non return policy?