1994 Ram 1500 Won't shift into overdrive
 

Hello all! I'm new to this forum, so bear with me!
I'm chasing a problem with a 1994 Ram 1500, 5.2 2wd/ This was my grandfather's truck until about a year ago when the engine blew up. It had probably been knocking for months, but he's 90% deaf, so who knows lol. Anyway, my brother-in-law bought it from him, and we put a used engine in last summer. It runs great now, other than a slightly high idle (about 1100), but the main issue is that the transmission won't shift into overdrive ever since we did the engine. Actually, it could have been doing it before, but I have no idea, because, again, Grandpa's nearly deaf, so he wouldn't have noticed... It had code 37 stored, pointing to the TCC/OD solenoid. We went ahead and replaced that, since it needed a tranny service anyway. I think (key word, think) that helped the TCC to start working. Not certain on that one, but it's definitely not going into overdrive, and still has code 37. I've checked continuity from the connector on the transmission to the PCM, and it checks out. I have power to the center pin of the solenoid connector with the key on. The O/D off button works as well, the light comes on when you push it, and goes out when you push it again, but it doesn't change anything driving wise. The fluid looks slightly low, gonna go get some tomorrow. I think he might have been checking it in park instead of neutral. Any ideas? Just for the record, at 55, my RPM is about 2200.

Does your trans have the temp sensor in the front fluid line to the cooler?

37 Torque converter clutch solenoid CKT or park/neutral switch failure. Wonder if the PCM thinks the trans is in neutral, or park...... it certainly won't engage O/D if that's the case.

Welcome to DF!

Thanks for the quick reply!
I don't think it has the temp sensor. It would be in one of the lines, right? And close to the transmission, not up by the cooler? I just crawled under to look, and there's nothing in the lines from the transmission up to where I lose sight of them up by the engine. Also, I thought I read somewhere that the sensor was part of the tow package. Not sure if that's true, but this truck doesn't have the tow package.
That's an interesting thought about the park/neutral switch. I'll have to look into that too. Would it even move at all though? I guess I'm used to newer stuff where it's all electronic.

Yeah, the temp sensor would be right close to the trans, and very obvious. So, that ain't the problem......

Do you have a scanner that can read live data?? That should tell you if the PCM thinks the trans is in park, or neutral.... I *think* it gets clued in on that.... The first three gears are purely hydraulic.... computer has zero control over those.... TCC and O/D though, are both via the computer.

I do have a scanner, but it's OBDII. I thought this truck was OBDI. I didn't see an OBDII port under the dash.

Yeah, 94 is OBDI..... I don't think any of the parts store scanners support that any more....

Try starting the truck with the shifter in D..... See what happens.

Funny. I just came back to say "well I tried starting it in D", and then I see your post.
It won't start in anything but P or N. I guess that exonerates the safety switch...

Indeed. That would imply that the switch is doing its job. That leaves wiring, or PCM...... PCM engages O/D by simply grounding the circuit. If the engine is running, the solenoids have power..... Check continuity of that particular wire, and make sure the connector at the PCM is nice and clean. If the wire checks out, that leaves the PCM is the issue.....

Ok, I had time to do some more testing tonight. I put the truck up on jack stands so I could "drive" it without moving. First I back probed the signal wire at the transmission connector (OR/BK, connects to pin 54 on PCM), and hooked my test light between that and battery positive. Started the truck and got it up to speed, and around 45mph, the light came on, so that tells me the PCM is indeed commanding overdrive. Then I disconnected the transmission connector and used flex probes and test leads to connect the middle (feed) pin on the transmission to power, and the OR/BK pin to a wire I could connect to ground. Again, got the truck "up to speed", then connected the ground wire, basically hotwiring the solenoid. Got a very small spark (telling me there is continuity through the solenoid), but no change in rpm, no sound, nothing. I tried the same on the brown pin (that would connect to pin 55 on the PCM), which I believe is the TCC solenoid? Just for the sake of being thorough. Same result, or lack thereof.
So here's where I stand. The PCM is good. The problem lies somewhere within the transmission itself. Either my brand new solenoids are bad, or whatever hydraulic system they control is not responding when they open and close. Any ideas? Seems odd to me that both solenoids would be bad, or that both hydraulic systems that they control would be bad, when the transmission shifts just fine from 1-2-3. Or am I wrong in my assumption that the third pin is for the TCC solenoid? Either way though, one of those pins controls the OD solenoid, so it should have gone into OD during one of my tests.

You could do a pressure test, That will tell you if you have pressure going to the od. If that's the case then something in the od is not right.

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