[wam18jr]

Good Afternoon (at least it is right now),

My 1996 Dodge Dakota, 5.2L, 5-speed manual transmission, with a 3.90 rear end has a problem with the speedometer. After four years sitting in the barn, nature taking it’s course on my truck, I replaced “the computer” (I assume the PCM). After all the usual tune-up and cleaning, the truck runs beautifully. He has 134601 miles of hitch I put on lol of them. I have checked many of the forums and am unable to find my specific problem.

The speedometer will read 20 MPH, at most, when I am actually doing about 60 +/- and kinda creeps up to that slowly. The tachometer seems to work just fine, as does the odometer and trip indicators. I have no warning lights, and have replaced and checked all the bulbs. I hook up my OBDII reader and get no codes (That’s another matter. The reader seems to be working, but I am not sure if the reader is compatible with the vehicle? It works fine on my Honda.). The cruise control has an intermittent issue in that it will sometimes fail to turn on, at other times, no issues. This was an issue long before the speedometer failed. As ridiculous as it sounds, it seems if I honked the horn, the cruise control would then turn on when I push the button. 🤷‍♂️

So far I have replaced the speed sensor on the transmission and the ABS speed sensor on the top of the rear differential. The problem still exists. My thinking:

1. Has the speedometer pinion gear in the transmission has gone bad with age or has it become warn and is not spinning properly? The problem here is wouldn’t the odometer and trip meter stop working too? I checked and the odometer is measuring miles properly according to highway mile markers.

2. Is there some sort of wiring issue between the speed sensors and the speedometer? That said, I would think an electrical wiring issue would be all or nothing, not showing such a slow speed.

I am really puzzled by this issue and would love to get it fixed. My OCD is in overdrive!

Thanks for you review of the post and any input you might have!

Bill

 

[immattj]

I am assuming that the speedo was not working correctly before you replaced the PCM?

 

[immattj]

. . . I don't know how similar this would be on your '96 as that on a gen2, but the reason I asked about that was not too long ago there was a thread that generated a short discussion related to an inaccurate speedo on a Dakota with a reman PCM, and the member, OldMarine, provided this:

"I have a manual transmission in my Dakota, and that sensor is also used for the speedometer signal to the PCM. But on vehicles with an automatic transmission, the output speed sensor on the transmission is the source for the speedometer. (The PCM needs to know the input speed and output speed of the transmission to control and verify selected gear range, shift points, etc., so it also uses the output speed sensor for the speedometer signal.)"

However, his Dakota is a gen2 and his reply was to someone with a gen2.

But his theory on that one was that it was possible that the PCM the OP on that thread had aquired was not programmed correctly for the VIN (tire size & rear axle). What your speedo is doing isn't the type of error that I would think would be caused by a mismatch of those factors, but still, on a gen2 with manual trans it does appear as if the PCM directly affects what the speedo is doing.

 

[wam18jr]

Thanks!! I am going to check on the programming of the PCM and see what I can do. I’ll keep you updated on the progress.

BTW you are correct, the speedometer was working fine before the PCM change.

 

[immattj]

I take it that you picked up a reman PCM, & did you provide them with your VIN so they could flash it accordingly? I don't know much about this subject, but I am kind of thinking that there would be a difference, for example, between the PCMs for an AT & a manual. (But from all else you have indicated, it runs pretty good with that PCM, so it couldn't be too far off.)

And, as I typed previously, I don't know for certain that those notes, related to a gen 2, that I pasted in my reply above this one, would necesarily apply to a gen 1 . . . but this

BTW you are correct, the speedometer was working fine before the PCM change.

makes me kind of suspicious that they probably do.
I think that the relationship between the PCM & the speedo on a '96 would definitely be worth investigating.

Good luck with your resurrected Dak!