I am working on a 1992 Camaro 350 tpi car automatic. Several weeks ago, the speedometer quit working, so I replaced the VSS in the transmission. Speedometer still did not work. The car then started blowing the gauges fuse. Found a short where a wire was touching the header and burned through the insulation. Fixed the short and replaced the fuse. Everything including the speedometer started working. A week later the speedometer quit again. Found the positive battery cable on the battery was slightly lose. Tightened it up and the speedometer worked for about a week. It will now occasionally work after hitting a bump in the road. Connected up the laptop to the computer and it shows a speedometer reading all the time. Bad connection at the speedometer circuit board? Bad circuit board? Any help appreciated.

 

If you’re seeing it in the datastream, check c207 for being tight and corrosion free. It’s probably the ip connection or a issue in the cluster.

 

I just had a somewhat similar situation; No speedo but the "computer" could see the VSS input. Your situation is the same in that you've done some work & now you KNOW a few things: The VSS is working so the speedo gears, the tranny VSS, and wiring TO the ECM is good. The TPI / Fuel injected cars don't use a VSS buffer like other cars and the speed 'data' is handled by the ECM. You KNOW the VSS input circuit is OK because you can see the VSS readings when scanning the ECM. From there,.. everything else is still unknown. This image is from a 90 Camaro:



Your bug could be ECM speed output, a bad connection @ the ECM connector (plug C1 terminal B11), a bad dash harness connection (plug C207, terminal D), the Cluster connection (plug C2, terminal C8) or the cluster itself. ( I doubt you have a bad ground - but you can check those - just in case !)

(** In my case I plugged a 1994 radio into a 2001 Chevy and the speedo quit working (during a tranny swap). The 01' speedometer output circuit was feeding the radio & getting "interference" from the 94 radio,...... and killing the speedometer signal to the Speedometer that was on the same circuit.

 

Got to looking at the wiring diagram and since the fuel gauge and the voltmeter use the same 12 volt source and work correctly I have ruled out the 12 volt source as an issue. The fuel guage and the speedometer use the same ground and since the gauge works correctly the ground would seem not tobe an issue. I cross checked to the other gounds and all was fine. I checked the wire from the ECM to the speedometer it it tested good. Eve wiggled the wire around. Pulled out the circuit board for the speedometer and one of the resistors appears to be burnt.

This is my sons car and got some new info today. The speedometer quit working when a wire shorted out to the exhaust. The short was fixed. When the fuse was replaced the gauges started working but not the speedometer.. I worder if the sort caused the resitor on the board to fry.