Transmission Issues

[BizarroStormy]

So I just completely lost power with my overdrive gear selected today, the engine will only go up to 2000 rpm and barely creep along. If I switch it to the third gear position it drives almost normally but still sluggish and if I switch it to the 2-1 position it drives normally.

I checked the transmission fluid level and it is high, but has always been high since I got the truck about a year ago. The color of the ATF was still pink/red, with no smell of any kind.

This truck has about 220k miles on it, don't think the transmission has ever been worked on. 

Any idea what could be going on?

 

Thanks in advance 

[omega_rugal]

the transmission is not shifting, let me guess, if you start in 1-2 and go throu D and OD manually it drives ok?

[BizarroStormy]

Just took it out for a ride around the neighborhood, and that is it exactly! I was even able to get it up into 4th gear manually. Very strange experience shifting an automatic like a manual. 

I checked the transmission fuse and it is fine, so I guess my TCU is fried? 

 

[omega_rugal]

43 minutes ago, BizarroStormy said:

I checked the transmission fuse and it is fine, so I guess my TCU is fried? 

 

is it getting 12v? is it properly grounded?

[BizarroStormy]

I was able to get a 4 ohm ground from the plug and confirmed that it was getting 12v on one of the pins. 

 

[omega_rugal]

weird, a TCU that dies all of a sudden... try with a known working one before buying, also read this

 

https://www.naxja.org/forum/showthread.php?t=1053970

[BizarroStormy]

The TCU has been resurrected! 

I figured I couldn't break it more than it already was so I pulled the casing off it. The board looked great except for one small burn mark under the 100uF capacitor. Looks like it burst downwards and maybe took the resistor next to it out with it. I dug through my electronics bins and found a close-ish resistor and a 400v 100uF capacitor. I "desoldered" the broken components and added my junk bin finds and my truck shifts again! 

 

Thank you so much omega_rugal for helping me diagnose the issue! 

[ComancheKid45]

Nice fix. I wish I was half as confident with electronics as you are. Haha

[omega_rugal]

2 hours ago, BizarroStormy said:

I figured I couldn't break it more than it already was

 

i like that attitude, nice to know someone who knows to handle electronics too

[AZJeff]

21 hours ago, BizarroStormy said:

The TCU has been resurrected! 

I figured I couldn't break it more than it already was so I pulled the casing off it. The board looked great except for one small burn mark under the 100uF capacitor. Looks like it burst downwards and maybe took the resistor next to it out with it. I dug through my electronics bins and found a close-ish resistor and a 400v 100uF capacitor. I "desoldered" the broken components and added my junk bin finds and my truck shifts again! 

 

Thank you so much omega_rugal for helping me diagnose the issue! 

You might want to secure the new, much larger capacitor.  In the electronics assembly biz, we used "elephant snot", a kind of adhesive that is semi-pliable.  A hot melt glue gun would do nicely.