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Old 07-06-2010, 07:45 PM   #4 (permalink)
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I know that the 88-91 cars with MPFI will throw a CEL at you when the speedometer stops working. But it takes some specific circumstances to make it come on; I think it will come on if the ECU sees you are over 2500 RPM with the throttle closed for more than a couple of seconds, while the speedometer doesn't move. That's not quite it (or you could get the CEL to trigger by revving up in neutral) but it's something like that.

On those older cars, though, there is a spinning cable from the transmission to the speedometer, and the VSS is actually inside the instrument cluster. I think the newer cars have the VSS on the transmission itself, and the speedo is all electronic.

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