Speed-o doesn't work....Help a gal fix her rig!

[Sluice Sally]

Question for you guys, we just bought a '90 suburban, and the speed-o is stuck at 68 mph. How hard is it to find out whats wrong and how to fix it

Thanks in advance,
Jen

 

[Jason4x4]

sounds like a bad head in the dash, if it was a cable, I would think it would be stuck at 0, if you were to put a used one in it, it probably won't be accurate, so my advis would be to go to a speedo shop, they can probably fix it and calibrate it.

 

[dyeager535]

Your speedo doesn't use a cable. If you've got a scanner, it would be pretty easy to determine if it's the VSS or wiring, or if it's the speedometer or speedometer wiring.

Autozone is supposed to let you scan a vehicle for free, you just need to take it for a drive with the scanner hooked up. If speed reads correctly, it's the speedo or speedo wiring. If it's a free and easy check, go for it. Can't hurt.

It would be odd for it to stick on 68MPH though if it were a VSS or VSS wiring issue, I will say that. I'd be looking for a wiring issue. Bad ground or power to the gauge. As I recall, the speedometer draws 12 volts from the same source as all the other gauges, (and shares a common ground as well) so if the other gauges work, there is power and ground to the speeo. The connector for the speedometer to the printed circuit board is robust too, but worth checking.

Those speedometers are a dime a dozen (or should be) if you rule out wiring, just replace it with another used one.

 

[Jason4x4]

iirc, autozone only scans obd II, and I don't think they have a data line capable scanner, just a code puller.

 

[BKinzey]

So where is Pollock Pines and who has a scanner near her?

 

[resurrected_jimmy]

1st generation scanners are cheap its worth just getting one

 

[Sluice Sally]

So where is Pollock Pines and who has a scanner near her?

Pollock is about 1 hour east of Sacramento...or....45 mins west of S.Lake Tahoe on hwy 50.


So how does this scanner work

 

[dyeager535]

Scanner plugs into the "ALDL" port under the dash. Stock TBI trucks I believe it is under the lowest metal lip.

Anyway, they let you see the data the ECM is seeing. No they aren't "real time" (slow data transfer rate) but it's enough to see whether the speed sensor signal is actually there and correct or if something is going on with it.

 

[goldwing2000]

Bfh

 

[k204dr]

everywhere i've read, only the 91 suburbans didn't use a speedo cable. I would look underneath and see if there is a cable. sounds like the speedo is screwed up if its stuck like that.

 

[dyeager535]

Everywhere you have read is wrong then.

'90-91 "old body style" trucks, all but one ton, were NP241's with VSS on the output shaft housing. Which is why the cable drive NP241 (1989 only) is so rare.

205's MIGHT have been cable 1990 and earlier, but 1991 they were VSS as well.

 

[Sluice Sally]

Thanks for the help...of course, we haven't had any rain a month, and now is pouring. I was hoping to get to know my burb better this weekend. We picked her up on Wed night.

I'll tinker a bit tomorrow, and hopefully someone will be around here if I need any help

Jen

 

[dyeager535]

This should be a fairly easy fix, so don't feel like it may be a real big problem.

 

[Sluice Sally]

This should be a fairly easy fix, so don't feel like it may be a real big problem.

I'll keep you updated

 

[BulldogK5]

This sounds close to the problem I am having on my 90 K5. The speedo will "work" some of the time and other times stick at any speed that it has gone to during the drive. I say "work" because of the 40" tires that have thrown off the calibration.

Welcome aboard.