O/D how does it work

More of the puzzle.



So there is obviously continuity from the switch to the ECM, and the ECM is energizing the ODLP line to cause the light to come on when it is pressed so there is continuity there. But for some reason, the ECM is determining that it can't keep O/D off and when the switch is released, ODLP turns off.

The only other thing I see are the solenoids at the bottom of the diagram below, as well as the cruise control ECU that has an OD line. Maybe cruise control is on? Or it is on and the bulb is burned out? Seems like a simple system, but in the end I think it seems to be limited to the ECU programming not wanting to turn OD off, maybe related to the cruise control ECU.

 

When you are cruising along at say 55 mph on level ground, the trans should be in over drive and the torque converter should be lockup. Can you confirm that is what is happening on your truck?

If this is so, when you push and hold the OD off button on the shifter, the light turns on, does the trans drop out of OD at that point? You are still going 55 when doing this. If it does downshift (drops out of OD), what happens when you release then button? Does it shift back into over drive followed by converter lockup?

 

What year is your diagram from?
2002?

I only have 2003 available to look at.
And it doesn’t show the CC signal OD to OD1

 

The O/D off button on the shifter is a latching switch. There is something wrong with your switch. Replace the switch and it will solve your problem OP.

EDIT: I just realized that 01-04 and 95-00 use a different circuit for O/D. The switch in my 99 is definitely latching. When I press it in, it will physically stay further down until I press it again to release it. I don’t know how they function in 01-04 trucks since I don’t have one. Sorry if I caused any confusion.

In the 03 diagram it is called [shift lock control relay]. This could mean that there is actually a relay integrated into the switch.

I have attached wiring diagrams for both a 1999 and 2003

 

It's from a 2001 manual I found on the internet. I'd be surprised if they were significantly different. I am pretty sure that cruise control overrides the OD off setting. This is why it's a momentary switch and just a "request" to the ECU, and the ECU determines whether it will comply based on some other factors (like, is cruise control on). Someone that has a 1st gen could test that theory, sadly mine has been gone for many years.

 

This is for a 2003 and what I am referring to for the O/D circuit and trying to figure out how that works

 

All years seem to be tied to ground with the switch. If not latching, then momentary. If momentary, then ECU detects ground pulse and then internally ties to ground to illuminate light after acknowledging external ground connection from switch. This makes it more complicated internally to detect another ground connection, so it'd be odd. Notably, we cannot see if pressed in is Normal Open or Normally closed on the 03 diagram.

Are you pushing the switch in all the way? Idk why they'd move away from latching.

 

My recollection is from my 99’
It operated like @nzbrock stated above.

I’ve had no luck finding the workings of a 2001-2004.
Maybe someone with that year can try theirs and let us know how it works.

 

When I activate mine it is instant, regardless of temp or speed.

 

Thank’s everyone I was working of the wrong diagram. We got it working as described and appreciate all the help. I thought I would update my post with a look at what we are working with. Now we can turn off the overdrive and pull through the duff. Go fast or go home!!!

 

I have this switch completely pulled from the vehicle. As soon as I have an extra moment to rifle through a parts box, I'll grab a pic or two. It absolutely is a push in to activate (in this case to enable OD, 'O/D Off' dash indicator is NOT illuminated) and push a second time to disable OD ('O/D Off' dash light IS illuminated). The switch is a locking/latching switch.

It really is a funky design and I'm surprised it doesn't fail more often. There is a little spring in there that helps to manage a plastic piece that when engages slides a certain way to lock a little plastic nub.

The part# for the Dk Charcoal interior is: 8472235210B1. It was replaced with part# 8472235210C0 (pictured below). It can be taken apart but I wouldn't advise it. The spring can go flying easily so if you do decide to remove the internals from the outer housing, be aware of this. I found out the hard way and had to hunt for that pesky spring when it went flying in the cab. Dumb ass me wanted to swap in a black T4R shifter handle but wanted to keep the charcoal button. lol.

For anyone who is having difficulty with this switch staying engaged/locked, just replace the entire switch assembly and call it a day. It's still going to be a pain to dissasemble and feed the switch into the shifter handle but its better than trying to tweak that little spring thing.