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Speedometer doesn't work


19k40rocky
07-12-2005, 11:13 PM
I have a '90 Grand Am with 2.5L engine and 3 speed automatic. The speedometer does not register. Can anyone tell me how to test either the speed sensor on the transmission or the speedometer itself to tell which is component is the problem? thanks for any advice you can give me on this!

Ridenour
07-13-2005, 01:06 PM
It may be a funciton of the VCM (Vehicle Control Module) or you could have a loose connection on the backside of your instrument cluster - not sure of the layout, but if there's an easy way to get to the backside of your cluster, it might be worth checking out.

19k40rocky
07-13-2005, 11:35 PM
Is there any way to rule out the speed sensor since it is the easiest to get to?

19k40rocky
08-05-2005, 10:52 PM
I'm back with the same problem but a few rule outs I think. First, during a road test the speedometer did register about 10 mph when I think I was running around 50mph and when going around 30 it probably is registering 2 mph. I tryed a VSS that was known to be good and it still did the same thing. I also pulled the speedometer and plugged in one from a salvage yard that was suppose to be good and got the same response noted above. Other information is the cruise control doesn't work either. It also started throwing a lean mixture trouble code but the O2 sensor is new. I am wondering if these things are connected somehow. All the connections seem to be good. Can anyone tell me what to try next? All help would be REALLY appreciated!

skibum1111
08-06-2005, 05:49 PM
Sounds like either a broken wire somewhere or a bad vcm. Follow the wire from the sensor back to the vcm, test both ends. The easiest way is to find a wiring diagram and use a multi tester on the wire, unplug it from the speed sensor and from the vcm test for a complete circuit, then test from the vcm to the instrument cluster. If these two come out ok, then the vcm is probably bad. That would also cause the cruise control not to work.

19k40rocky
08-15-2005, 04:40 PM
Just an update and a big thank you. It ended up being a faulty electronic control module causing the problem. I got one out of a salvage yard and it works great now. Thanks everyone for your help again!

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