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.