big bollas

Not sure what happen but I was driving my Z after it sat for a few weeks and noticed that the speedo was not working ?
The RMP one works , any ideas or info as to why this may have happened or what I should look at to try and fix it ???
Thanks for any of your input

Bill Dearborn

Does the HUD speedo work?

Bill

big bollas

Nope , nada !
But the rpm does.

forg0tmypen

Interested in this...never heard of this happening. Should be an easy fix I would think.

big bollas

Well I went over all of the connections yesterday and did not find anything out of the norm, I disconnected and then reconnected any connections I could find from the tranny to the ECM but it still did not fix it. So what I did when I was done with that was diconnect the battery and let it sit over night and see if something will reset it self
"wishful thinking" but I am giving it a shot. I would think that I would have gotten a light on the dash for this but I dont have any on.
The other thing I noticed was that the odometer is not clocking any miles on it? This must all tie in some how...

Still looking for help...

jbp8653

There is a plug on top of diff that came un plugged on one of mine that stopped the speed-o cold. Sits directly on top and is a snap in plug. Hope this helps.

big bollas

Is it on the diff or the gear box ? Have not seen anything on the diff.
Hooked the battery back and still the same so that did not work .

jbp8653

Very top of the diff. Electric plug in. Hard to see when standing under car on lift.

big bollas

Would this be on the left , middle or right side of the diff ?

jbp8653

Top middle

big bollas

Cool , I will give it another shot today.
Thanks.

Duke/Earl

Guys beware driving with a non-functioning speedometer. The lockout for reverse is electronic and tied into the speedometer, so when shifting into 5th you will very easily get reverse. The noise helps alert you when this happens. After some transmission work on my '05, my dealer forgot to hook-up the speedometer. I found out on the freeway, a slight case of reverse grinding. Immediately returned to get it rectified.

SnowyATX

Ever solve your problem?

big bollas

No still have the issue. Any suggestions?

KENS80V

The speedo sensor on top of the diff is held in with one small bolt. Couldn't hurt to just change it out. The part number for it is #12369458. PartsTaxi sell it for $36.59.

This 2 wire sensor sends the pulses from the ring gear in the diff to the ECM. The ECM interprets this signal and then sends it via 1 wire to the instrument cluster, radio and HUD.

SnowyATX

Mine is intermittent as identified by it throwing codes. I've followed most of the manual debug procedures at the ECM but not all. I'm going to throw in a sensor and see if that fixes it. Its going to be a bizatch to get to though. BTW, there is a big internet company out there that also sells books that also sells this item.

tim414

I wanted to chime in. I had this happen but, it was NOT my Vette. It was my Yukon. The analog gage is operated electronically and the speedo itself failed. The cluster in dash needed to be repl'd. Had faulty electronics behind the gage. It was recieving the proper signal, just wasn't doing anything with it. Later GM recalled it (I had already repl'd it or dealer did).

Might want to ask dealer.

KENS80V

If it was just his cluster that wasn't registering the speed I'd agree but the HUD isn't showing a speed as well. They both receive their signal from the same wire coming from the ECM. In my opinion it could be one of three things. The ECM is bad, the speed sensor is bad or there is a break in the wiring circuit somewhere.

dmuellenberg

Really - you haven't fixed it in over 8 months?

z10

Had the same thing happen to my 2004 Envoy. It was in the instrument cluster.