the speedometer is erratic or at zero

1994 CHEVROLET TRUCK

193,000 MILES • V8 • 2WD • AUTOMATIC

JOHNEFLEMING

MEMBER
2 POSTS

I can drive the truck for 15 miles and if I stop for any reason the truck then begins shifting erratically, the speedometer is erratic or at zero, and the truck sometimes appears to remain in limp mode, stuck in 2nd Gear. Almost always the brake warning light comes on. I have had the transmission speed sensor replaced and the ignition switch replaced. The transmission guy said that he checked the 'dark', which I believe is the speed sensor buffer and it was okay.

May 4, 2008 at 10:05 AM

MASTERTECHTIM

✓Experienced Mechanic
4,750 POSTS

you need to check for ac voltage at the drac (digital ratio adapter controller) and make sure your getting a signal there from the vehicle speed sensor. if you get ac voltage there when its inop then replace the drac

Apr 21, 2021 at 5:30 AM

JOHNEFLEMING

MEMBER
2 POSTS

I tested the voltage from the vehicle speed sensor at the drac, it rose steadily up to over 12v when disconnected from the drac. When I connected it to the drac, the voltage was erratic and would not rise even millivolts.

Does this point to the drac?

Apr 21, 2021 at 5:30 AM

MASTERTECHTIM

✓Experienced Mechanic
4,750 POSTS

the voltage from the speed sensor is around 1.5 ac volts at slow speed. if you get a close reading and still no speedo at all then yes i would suspect drac. i worked at gm when these trucks were new and i remember replacing alot of them, so they do fail.

Apr 21, 2021 at 5:30 AM

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