Vehicle Speed Sensor Testing

[RMcKinney]

Is the "DRB scan tool" only way to test the "Vehicle Speed Sensor?
1995 2500 bone stock with 274000 orginal miles.

 

[fest3er]

[This applies mostly to my '98. Your '95 uses a sensor on the transmission to detect vehicle speed; it may be connected directly to the PCM, but the manual test method is largely the same.]

You can unplug the sensor at the CAB (Controller, Anitlock Brake) and put a multimeter on it, jack up the rear axle and pu tit in gear. You should see perhaps 1VAC at idle in 1st gear, and possibly 2.5VAC or more at idle in OD. Zero volts means there's no signal reaching the CAB. IIRC, the voltage drops to under .4VAC at around 3MPH, which is too low for the CAB to sense.

If you have good signal entering the CAB but no signal reaching the PCM, you probably have a bad CAB.

Do the same at the rear axle. You should then be able to determine where the problem is (failed tone ring, sensor or sensor wiring; or failed twisted pair cable from the sensor to the CAB).