Testing electric speedo?

[usar17]

Anyone know how to test the signal wire to the cluster? My aldl data is showing proper speed but my speedometer stays at zero. 1991 cluster.

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[yevgenievich]

Would need a function generator or 555 timer based small circuit. Or put an oscope on the wire going to the gauge and verify if proper signal is present.

 

[usar17]

Not able to use a multimeter to any degree on the signal wire?

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[chengny]

You can use a standard VOM to test speedometer input signal - just set the voltage to AC. Here is the diagnostic chart from the 1991 Light Truck Service Manual:

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Strange thing is that nowhere in the diagnostic does it mention that the speedometer might be bad. The only options are bad wiring, bad DRA or bad VSS.

When checking the voltage don't expect much. I would image that it would be similar to the voltage generated by an ABS wheel sensor - maybe 500 - 700 mv. Set your meter to the lowest range.

 

[usar17]

I have a 1994 ecm/VSSB but a 91 cluster which usually takes a drac. Could that be an issue? 2 different signal styles? If so is there a way to overcome this?


-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208

 

[usar17]

(Removed double post)

-Shawn
1985 Chevy k10 w/ 92 TBI, 94 4l60e, 91 NP208