Hello everyone, I hope you all are doing well. This is my first time posting, FYI!

I have a 1992 F350 IDI with an aftermarket Banks turbo. I’ve utilized this website several times with past issues and have had great success. One of the remaining issues I’m struggling with is “limp mode” on the truck.

First off, the truck had a transmission rebuild/retime at 82,000 miles (it currently has 102,000) from the previous owner. However, it has shifted harshly since I’ve owned it. Initially, I changed out the VSS with a new one from Napa and it made the speedo tick back and forth. After researching, I found that many of the VSS’s don’t operate correctly right out of the box. I went and pulled one off of a junkyard truck and it seemed to help a little bit with the harsh shifting.

This was about six months ago. A few months after that I noticed my O/D blinking after driving up my driveway. I didn’t think much of it, as it turned off and didn’t reappear. Approximately two months later, though, the truck slammed into second and blinked O/D again. I turned it off and back on and it disappeared. I went home and pulled codes with the OBD-1 code reader and. Go no codes (for reference I don’t have any warning or check engine lights on). I was extremely confused because the computer isn’t storing any transmission codes. A few more months went by and she was driving fine, no limp mode. Then, yesterday she slammed into second again and blinking O/D light. This time I was prepared, and immediately pulled over and pulled the codes with the truck still running. I received no codes and by the time I got back into the truck (after approx. four minutes) the O/D light was off. Today, I was driving again and the same thing happened. This time, however, it didn’t shift harshly, I just felt her not shifting out of first while driving at a low speed. Sure enough, the O/D light was blinking. I came to a stop in the middle of the road, didn’t shift into park/do anything, and the light turned off.

I’m changing the tranny fluid/filter this weekend and seeing if possibly the filter is clogged and causing the tranny to overheat. I also pulled a tachometer off a junkyard truck just in case. Tachometer sensor read 2,889 Ohms.

Can anybody explain how in the world I am getting a transmission code light that 1) isn’t being stored and 2) randomly decides to disappear? Again, I’d like to stress that the transmission was just rebuilt. I don’t have a VSS code light or any other check engine light. Tachometer works fine. Speedo ticks a bit over 65mph.

I incredibly appreciate the posts and wisdom from you guys. Y’all are awesome.


Respectfully,
Aaron

 

there is a code, your reader is just not reading it. if i remember correctly, there is a way to jump a few pins in the test port and that will give you the trans code by watching the od light. the number of flashes of the light will be the code.
@ Mark Kovalski is our resident E40D expert. this ping should get an answer from him

 

Hello Tom, thank you for the reply. For the record, I am getting codes with my OBD1 code reader. They are just the normal 23, 74, and 65 from not doing the in-cab sequence. That being said, if I am receiving engine codes doesn't that mean I should be receiving transmission codes as well? I looked up a video on jumping the pins and all that did was cause the check engine light to blink (which my code reAder is already reading).

I've read through a hundred forums and I'm still confused on whether transmission and engines codes are pulled from the same place. In other words, if I was pulling a transmission code, wouldn't I be watching how many times the O/D light blinks rather than the check engine light?

 

Nevermind... I just reread your message and realized you mean jumping a different set of pins. I apologize, haven't had coffee yet.