O.K here goes. Speedometer doesn't work at all. I am getting VSS circuit problem code from ECM. Replaced VSS with acdelco new part. No fix. Then ordered a replacement cluster from ebay, from what I have found only a 92 3.1L cluster will work. New cluster had exact same tag as OEM cluster in car. Replaced no fix. Laid under the car while on stands in gear, shook wiring and plug checking for loose connection, nothing. Everything on this car works great but speedometer. Both clusters gauges all work except speedometer. I am thinking broken or loose wire. My chilton manuel shows no wiring diagram for 92 firebird 3.1L. What terminals (ECM or Back of cluster) or wire colors should I trace to find my problem. Any help would be great. This problem bugs the crap out me!

 

First, ANY cluster from 1986 to 1992 will work, but needs to have the full gauge cluster, and the 120 speedo is only on 90-92 cars. If you're setting a code 24, you're not going to have a working speedo because the ECM isn't getting a VSS signal AND it does the job of running the instrument cluster.

Second, raise the drive wheels, put the car in Neutral, and spin the wheels by hand while measuring for AC voltage (yes, I said AC VOLTAGE) at the VSS wires at the ECM (pins B9 and 10 in the SMALL ECM connector, yellow and purple). You should get around 2 VAC, IIRC, unless there is a broken wire between the VSS and the ECM connectors. Next, check the resistance of the wires between the ECM connector and the VSS connector. They should NOT be infinite (OL).

 

so with the code set in the ecm, and a brand new vss in tranny, you believe there is a short in wire from vss to ecm? if vss is getting signal to ecm there sholuld be no code right. will try to test wires at each end this weekend. this sounds like a fun project. wires run to passenger side of wire harness going into the car to ecm.

 

With a NEW working VSS, if the wiring is good and the ECM can read the VSS, there shouldn't be any code 24. If the VSS is good and there is a code 24, there is probably a problem with the wiring between. A short? Unlikely. Probably a broken wire either in the VSS connector or somewhere between the VSS and the body pass-through behind the passenger's side kick panel.

 

Thanks alot. I will let you know what I find. I hate wiring problems. so time consuming.....

 

6-107 and 6-108 are wiring diagrams for a 92 in a chiltons manual. At least it is in mine.

 

That Chilton's manual may be as thick as my 92 Factory manual, but it's as useless as a Haynes. No details whatsoever in the wiring diagrams (those diagrams are what is pasted all over the AutoZone site). I'm sure that what you paid for the Chilton's, you could have bought a used FSM.

 

I agree. Mine was pretty much free but it does lack A LOT of detail where its needed and even the "detailed" views of things are horrible.

 

Subscribing for info.

 

I tested wires starting at transmission, ending at ecm input location. both wire yellow and purple completed circuit. Turned vss sensor by hand and showed ac voltage at ecm connector. But when installed vss in transmission, turned drive shaft no voltage? after reinstalling vss about 5 times, apparently vss gear was not coming into splines with gear in transmission tailshaft. I was about to order a new gear for vss sensor, and the last time in installed it, voltage showed at ecm, speedometer working perfect. I guess if it stops again i need a new gear, or maybe it wasn't seated correctly. Thanks everyone for all the help.