1995 ram 1500 4x4 auto transmission. About 95k miles and the truck is clean as can be.

I've been looking for a thread that answers this, but what I can find comes close, but not exactly. So if I missed it, my apologies.

I replaced my leaky transmission cooler lines. I had seen and read quite a bit about just cutting out the 2 sections and putting in some 3/8 tranny hose clamped properly (I flared the ends for extra hold). Doing this takes out the check valve, which I consistently read as being nothing but problematic as it can get clogged.

Welp, after replacing the lines the first drive was great. Zero issues. Into work and back and overdrive was present and shifted well. Drove it the next day and now overdrive is gone, but still shifts well through 1st to 3rd. The overdrive switch on the dash works properly.
My thinking is that on this particular year that check valve has a roll in building pressure to engage the overdrive switch. But then again I read that the overdrive on this tranny is engaged electrically, and has nothing to do with pressure.
Should I go get a full line that has a check valve in it, or is it possible that this is coincidental and it's a relay or something??
Greatly appreciate any guidance and help!

 

Cooler lines have nothing to do with O/D. Unless they are clogged up.... in which case, the trans heats up.... Yours doesn't have a temp sensor for the PCM to read. (although, there was one that was part of a couple different optional packages..... if you have it, it would be on the front line, very near the trans.)

O/D is indeed purely electrically controlled. PCM just grounds the circuit for the solenoid. If it grounds the circuit, and doesn't see an RPM drop, it will set a code. If it isn't setting a code, then, for whatever reason, it isn't grounding the circuit. On the OBDI trucks, I am not aware of any criteria the PCM would use to decide NOT to shift into O/D, aside from vehicle speed to low.

 

Would this guy be that temp sensor youre talking about? It seems evertime i have an odd issue with this truck i find out that it's the weird model that had some different part or whatever. It's a cali coded truck as well. Also, this is suppsed to be the 47rh transmission i thin . Is the overdrive solenoid on the outside of the body near the linkage? Greatly appreciate your reply! I'm learning more and more.

 

That is the temp sensor. The O/D solenoid is inside the pan.

 

The PCM uses throttle position, MAP, tachometer, vehicle speed, and temperature to control lockup.
You might have knocked a piece of dirt loose that is lodged in the valve body, just a possibility. Don't spend money without a proper diagnosis. The forum parrots will happily help you throw money at your problem from 1500 miles away.

 

Well, on a whim I simply disconnected the battery for a while, reconnected and drove it. Overdrive worked just fine! WTH
I've now driven it a couple times since and all seems totally normal. Drives great. Did I really re-learn something in the ECU by disconnecting the battery?
Thanks again for all of the advice and guidance.

 

It does wipe it's memory. You should do that anytime you replace sensors. Disconnect the battery turn the ignition like you are trying to start it for around 2-4 seconds, then reconnect the battery.

It also could just take a while to bring the problem back as the computer has to meet the criteria again.

 

I begin to think doing a PCM reset at the BEGINNING of troubleshooting might be a good idea.

 

So far so good. Overdrive has been kicking in normally. Now the issue, and this had started happening before I fixed the leak in the cooler hoses, is that while in overdrive at 50+ mph and having a slight load on it, such as going up a slight incline where there's not enough load to kick it out of OD, it stutters like crazy.
Research I've done on this I keep coming up with stutter and shifting issues in all gears. Mine is shifting just fine, it's just an issue in OD. Once it's kicked out of OD, problem goes away.
I keep finding similar stutter issues on diesels where they solve it with a noise isolator (grounding the wire coming out of the PCM it looks like). Is that specific to the diesels? Does this sound like an OD solenoid issue?
Appreciate any guidance/info! Y'all know your💩!

 

Noise isolator on diesels was to clean out the TPS signal. And it was mounted between the TPS and PCM.
I have '95 diesel, and it had all kind os issues with OD and TCC. First they didn't work at all, turns out to be brake pedal switch. Then it started to drop off OD and TCC altogether at once, without warning, going 55 mph down the road, in rain. Then withing a few seconds, it engaged them again. And after a while, same thing. So you couldn't use the OD in rain. Wet road was no problem, only rain. So I figured it must be TPS acting up, so I tried noise isolator with no avail. Then went to wire separate potentiometer, set to 2 volts. Only thing that I screw up the pins and grounded the PCM output to the TPS = burned circuit and no longer had TCC or OD at all! So I wired two switches to control the TCC and OD, and never again had any issues with either of them not staying engaged. It does stutter OD engaged and at low rpm's, but that's probably because injector pop-pressure is way low (need to rebuild them at some point).

But you might want to do a tune-up to your engine if not done lately. Might be just engine running rough on lower rpm's while OD is engaged.