Speedometer jumps

[Dust92]

In my 93, I'll be cruising between 50 and 55 and my speedometer jumps down to 45 or 40 then downshifts. Think it's the speed sensor? Anyone had this happen to them?

 

[Yeti_Owner]

It's worth swapping with a junkyard take off to test. VSS would be my first guess.

 

[Dust92]

Is that known to cause weird downshifting?

 

[Yeti_Owner]

Oh yes.

The transmission you have is computer controlled. If the VSS is sending nutty signals (IE your speedo jumps like you described), your transmission is going to assume you went from 55 to 40, and shift out of overdrive/unlock the Torque converter.

 

[Dust92]

Thanks for the info, I had a vague idea that's what it was doing but I wanted to be sure.

 

[great white]

93 has a DRAC module.

Speedometer drive is separate from the ECM input, which is separate from the cruise input.

If the speed sensor is pooched, you'd has other issues, like cruise would be wonky or won't engage. a loss of signal should also set a DTC, but DTCs are funny things sometimes and the don't appear when they should.

More likely, you've got a bad connection between the cluster PCB and the dash connector in the back. Try removing the cluster and reseating it in the dash.

Next likely culprit is the speedo drive motor itself.

then the PCB in the speedo.

Then the DRAC.

Then wiring.

wouldn't hurt to swap out the vss though. They're cheap and it's a quick swap out. That would eliminate it as a cause and it is a failure point common to both speedo and transmission.....worth a try.

 

[Yeti_Owner]

93 has a DRAC module.

Speedometer drive is separate from the ECM input, which is separate from the cruise input.

If the speed sensor is pooched, you'd has other issues, like cruise would be wonky or won't engage. a loss of signal should also set a DTC, but DTCs are funny things sometimes and the don't appear when they should.

More likely, you've got a bad connection between the cluster PCB and the dash connector in the back. Try removing the cluster and reseating it in the dash.

Next likely culprit is the speedo drive motor itself.

then the PCB in the speedo.

Then the DRAC.

Then wiring.

wouldn't hurt to swap out the vss though. They're cheap and it's a quick swap out. That would eliminate it as a cause and it is a failure point common to both speedo and transmission.....worth a try.

Are you certain? I thought the earlier one's had a DRAC, and 92-95 had a VSSB?

 

[///RAGMC]

Mine bounces around like that but no misfire.

 

[great white]

Are you certain? I thought the earlier one's had a DRAC, and 92-95 had a VSSB?

Same ****, different pile.

up to 91-ish the DRAc was integrated into the cluster. 92-93-ish it was an external DRAC, 93-95 was usually a VSSB, although it seems there's some odd balls out here that break the mold from time to time and you find a DRAC in post 93 models. Vans, like always, were weird combinations of parts until the next chassis model.

Difference on the external modules was essentially twice as many jumpers inside for calibration purposes.

 

[Yeti_Owner]

Ha! True!