92 2wd Dakota Sport overdrive not working
 

Hey. I have a Dakota with a 3.9 V6, and the overdrive doesn't work. I have read for hours on different sites about how to check the sensors, etc. I've checked sensors, output of the PCM, otherwise called the SBEC (I think), and haven't come up with anything conclusive. I have named this truck POST, for Piece Of ...... , so that should tell you that I don't want to invest much time or money into rebuilding the tranny. If it were a simple matter of replacing the OD solenoid, I would be willing to do that. But, isn't there a way to check it to see if it operates? It has 3 wires going to it, so shouldn't I be able to ground one of the two outside wires to check it? I'm getting power to the middle (blue) wire.
The only sensor I couldn't find is the transmission fluid temp. sensor. Someone replaced the radiator before I got the truck, and they didn't install a new temp. sensor, and the wire with the connector on the end is just hanging around the battery box. But, since this sensor (swich, actually) doesn't do anything until the temperature is 270 degrees or so, so it's apparently just to prevent the OD from engaging if the tranny is overheating.

Any help would be appreciated!

PCM grounds the circuit for O/D, and TCC, so, with the engine running, in park, you should see power at all three wires. (at the PCM.)

Remove the connector and put 12v to the center pin. With another jumper ground each outside wire and you may be able to hear an audible click inside the pan. The solenoid is submerged in fluid so that may muffle it. If you have a stethescope stick it on the pan. You can also set your meter to ohms and measure the impedence of the center pin to each outer pin. The coils for overdrive and lockup are the same so should measure the same.

That will at least tell you if the coil is good. Although coils rarely go bad...usually the problem is the lost ground from the sbec. The signal goes through four connectors...the main connector at the SBEC, a connector to the transmission/rear harness, the main firewalland the connector at the transmission itself. These connectors can oxidize over time so pull them apart and reseat them a few times. Also in the case of OD the signal also goes through a small transistor circuit behind the overdrive button in the cab. If this button/transistor have failed it could also prevent the signal from reaching the coil.

Thanks, Robertmee! Today, I did just that; with my ear against the pan (I don't have a stethoscope) I heard nothing when I connected either solenoid. It sparked (which is normal, especially with a coil), but made no discernible sound. Each coil measured 30 ohms from the center pin of the connector, and 60 between both outside pins.

I then took it for a test drive, since I don't know whether engine temp affects operation of the OD, and got no ground from either lead to the solenoid. I had two test lights hooked up; one for the lockup circuit and one for the OD, and whereas I had power to the center connector, neither light went on. Also, today (and this is an erratic occurrence) the light on the OD switch on the dash went on when I started the truck, and didn't go off no matter how many times I pushed the darn button. I wish I knew exactly how all the sensors affected the operation of the SBEC regarding OD. Then I might be able to determine whether it is a bad SBEC, or one of the inputs.

And the PCM isn't setting any codes?????

No codes. The only code has to do with the idle air control motor circuit, which isn't surprising. Haven't looked into that one yet.

Has TCC or O/D EVER worked on the truck?

I'm wondering how you know the OD is not working because you did not state how or when that happened. If you have an FSM it describes how to do a stall test and hydraulic pressure test for the OD. It sounds as if your OD solenoid has gone bad or possibly something in the wiring or circuitry is shorting the way you describe the off light coming on and off. If you unplug the solenoid it should drive normally as a 3 speed. You might do that to see what problems still exist with the OD out of the picture.

HeyYou, not since I've had it (I've had it for 3 years now).
onemore94dak, the truck does not shift into 4th gear, so that tells me the OD is not working. It drives normally as a 3 speed now, even with the solenoid plugged in; and since there is not ground connection through the SBEC, it's the same as unplugging it. What I don't know, like I mentioned in my previous post, is how all the sensors work in conjunction with the SBEC. I have checked the following:
TPS: working properly.
Oil temp sensor: not installed
RWAL sensor: putting out a signal, so I'm assuming it's working
OD control switch: working properly
I'm not sure what else provides information to the computer regarding the OD.

AFAIK the computer has nothing to do with the operations of the transmission. It is hydraulic unless you have something different from the 42 rh. I am not sure about the early 90's I know they changed it in 95 internally doing something with ports then the obdII 96 have a computer trans connection.

OK, well that's good to know! But, if the computer doesn't have anything to do with the tranny operation, why do the two wires that are supposed to provide the ground path to the solenoids come from there? I'm just assuming it's a 42RH, since it's a 3.9 engine.

The ECU does the go/nogo speed test for lockup and OD; the internal switch can override the go from the ECU for OD.

It's very simple; the ECU can be replaced with a vacuum switch and two pressure switches for all that matters ( see, for instance, the kit at https://transmissioncenter.net/shop/...iring-diagram/ )

RwP

Thanks, RalphP, I'll have to check that out!

incorrect....the OD solenoid gets its ground from the SBEC on any 42rh to 46rh.

This is what I did on my engine swap as I completely eliminated the SBEC. My OD and LU are controlled by two pressure switches and a vac switch using the TCI kit. FYI I also used a relay (repurposed my AC relay since I eliminated AC) and connected it to the transistor circuit on the OD button inside the cab. That way I can still turn off OD using the button. If you get to that point and need a schematic let me know.

But from your follow up tests if both the OD and lockup aren't working I'd suspect a connector somewhere. Using your same test light procedure move further up stream...start with the test light right at the SBEC wires leaving the connector.

From your tests your coils sound ok...you measured a load and confirmed that with the spark...if the coils were bad you'd likely have an open circuit and no load and no spark. If a coil overheated usually the windings short together thus effectively reducing the number of turns of wire in the coil. This could reduce magnetism and not allow the coil to pull in the plunger but you would see this as a reduced imedence....that you measured 30 ohms on both that's not the case.

Thanks, Robertmee, that's what I found. Also, the OD switch on the dash also goes to the SBEC. I notice you talk about a transistor in the switch, but I don't see one indicated in the wiring diagram for the switch; it shows an illumination bulb, a push-button switch (NO) and an indicator light to show that the OD is off. When I was trying to get the OD working a couple years ago, I took out the switch and took it apart to see how it worked; whether the push button switch was a toggle, or momentary. I didn't find that out, necessarily, but I DID break the darn thing, so I now just have a hole in my dash. The other day, when I resumed investigating this issue, I hooked up a push button switch (doorbell switch) and a 12v bulb, hooked up just like the schematic shows. The push button switch doesn't seem to have any effect on the operation of the OD. But, when I got in the truck yesterday to do one of many road tests, the light went on as soon as I started the truck. It didn't do that before. But, on my road test, no matter how many times I pushed the button, the light never went off.
Today I will try checking all of the wires that go from the solenoid and the switch to the SBEC, as you suggest.
I think I mentioned in an earlier post that I had connected 3 wires to the wires going to the solenoid connector on the tranny, and ran them into the cab, attached to light bulbs. At no time did the light bulbs light. But another thing I did is touch the two wires connected to the outside terminals on the connector to ground inside the cab as I was driving. Since I grounded the solenoid, shouldn't the OD have kicked in?

A few notes:

1) The transistor is inside the control module,which is that assembly with the light and the switch. There's also a diode shown in the 1988 diagrams.

2) How did you hook the light bulb up to the solenoid wiring? I don't see many ways that won't cause possible problems; but if you hook a 12V LED, positive to the center wire, negative to the switched wire, it should light up if the PCM is enabling the lockup or overdrive.

3) Try splitting the wire for OD and the wire for lockup from the connector, then running them into the cab. If you ground the circuit, you should notice a very small or a noticeable drop in RPM for the same road speed (TC lockup won't be but 100RPM or so, but the OD would be about a 1/3 reduction since it's like .7 or .67 OD ... that is, engine RPM will now be 70% or 67% or so of the driveshaft RPM in overdrive). If it's dropping, the lockup or OD is working.

Don't forget to open the circuit(s) before you stop the truck ... TC locked up will cause the truck to stall, and OD will kind of kill the performance for moving from a standing start *grins*

RwP

Okay, I did what you suggested, and there has been partial progress. I used two toggle switches, one for the OD and one for the TC lock. I got the convertor to lock, which I hadn't experience EVER before, but the OD still didn't kick in. I tried turning the switch on and off multiple times, thinking that it might break free if stuck, but to no avail. Next I'm going to go back under and see if I can hear the solenoid. And I'm going to examine the flow diagram for the tranny to see if, perhaps if the OD solenoid IS working, then perhaps there could be some kind of block in the fluid "circuit" that could be preventing engagement of the OD.

Check the part number on your PCM. I wonder if it is simply programmed for the wrong transmission.......

I think I know what the trouble is. The solenoid pack for the O/D and lockup is bolted to the right side of the valve body inside the pan. My truck experienced no O/D and the lockup would sometimes not release. The 3 screws holding the solenoid pack to the valve body had loosened, allowing the fluid to bypass the solenoids. Drop the pan and tighten the screws, and while you're there, change the filter and refill with ATF+4.

And BTW, there is no transmission temp sensor on a 92 Dakota. The PCM doesn't allow O/D until the coolant temperature reaches 60F, and doesn't allow lockup until the coolant temperature reaches 140F. So if you don't have a good coolant temp sensor (the 2-wire sensor next to the thermostat), neither function will work properly.

Thanks for that info! I'll be pulling the pan later this week, so I will check that out. My manual says that there is supposed to be a transmission oil temp sensor on the line close to the radiator; but I'll check out the coolant temp sensor and make sure it's working properly.

You will only have that sensor if you have some variety of heavy duty, or factory towing package.

Ah. Thanks! I'll let y'all know what I find out later this week.....

Well, I wasn't able to get to pulling the pan until today. So, I pulled the pan (Why, oh why don't they put a drain plug on a transmission pan?? What a mess.) and removed the solenoid assembly. When I attach positive to the common wire and negative to each of the solenoid wires, I can hear it click, but I thought I'd see the solenoid plunger move. There is no plunger. If there is, it's inside the end of the solenoid through the little hole. I poked a wire in there and held my finger on it loosely, connected the wires, and I could feel a tiny bit of movement, but that's all. Maybe a millimeter or less. How do I test the solenoid once it's off?

So, I don't know if any of y'all are still seeing this thread, but I replaced the OD solenoid today, and it works!! Thank you everyone who responded with helpful stuff!

Good job!

I just swapped out the trans in my own 92 because other than leaking in a spot that is a royal pain to access while in the chassis, (where the shift linkage passes thru the case) its OD was flaky, it worked when it wanted to and I never knew when that would be.
That, and I had a fresh one ready to go just collecting dust sitting here. One that I rebuilt about a year ago "just in case".... I will now rebuild the one that I removed, possibly to go into one of my '70s cars.
My truck just passed 204K miles, I now have 700 miles on the trans job, OD now works fine, every time. I think that I know exactly where within the trans my issue will be found.
Along the way I put in a TF-OD-jr shift kit, a product I have used and been happy with more than once in other transmissions, and for some reason it didn't work in this one. I will have to go thru that valve body and recheck the adjustments and see what went wrong.
I wound up taking the valve body out of the original trans and swapping it into the fresh trans about 150-200 miles after I put it in the truck, and once I played with the throttle kickdown cable til I was happy with that, it now shifts fine. This valve body that came out of the original trans, still has its original solenoids on it, I did not swap solenoids with the ones out of the rebuilt trans. If nothing else it verifies that the solenoids from the original trans are good, and that the issue is within the original trans itself, like I originally thought it might be..... in the tailshaft section ("overdrive unit") I debated pulling that off of the original trans and just rebuilding that and putting it back on, with the trans still bolted in the truck.... I've done that before... on the original trans 1,2,3 and R worked great.

I know this thread is over a year old but I'm hoping someone will see it and be able to help me. I have a '92 Dakota LE, reg cab, long bed, 2wd, 3.9l, auto, that was given to me. 98,000 and the body has zero rust. Paint, not so good. Interior is flawless. Both previous owners were elderly so no abuse, no strenuous duty.

TC Lockup does not work, OD does not work. {Cruise control doesn't work} Replaced: solenoids(changed fluid and filter tightened valve body bolts), VSS sensor, neutral safety switch, TPS, CTS and PCM. No luck.

Any ideas? This is a good truck, it needs the TCC and OD to function properly.