ERRATIC SPEEDOMETER

  • Tiny
  • thefiretech
  • 1993 Chevrolet Lumina
  • 144,000 miles

Hello
My speedometer is behaving erraticly. Once I get above about 50 mph gets erratic and goes to a reading of over 100 MPH and is never stable until it gets below 45.
Is it tied directly to the transmission via a cable or is from the ECM?
Any help is greatly welcome.

Thursday, September 22nd, 2011 AT 9:49 PM

9 Answers

  • Tiny
  • promechanic
  • Expert
  • 551 posts

It is likely that you have a bad VSS or vehicle speed sensor. The ECM gets a signal from the VSS and sends it to the speedometer. It is possible that it is an ECM or wiring problem too but not as likely.

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Thursday, September 22nd, 2011 AT 10:05 PM
  • Tiny
  • thefiretech
  • Member

Thanks for the reply.
Can you please tell me where the VSS located?
I have an old Haynes book bit I cannot find it.
Thanks

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Thursday, September 22nd, 2011 AT 10:27 PM
  • Tiny
  • promechanic
  • Expert
  • 551 posts

It is located on the right rear of engine on the transaxle.

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Thursday, September 22nd, 2011 AT 10:40 PM
  • Tiny
  • thefiretech
  • Member

I'm glad it wasn't a snake.
Thanks

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Thursday, September 22nd, 2011 AT 10:53 PM
  • Tiny
  • promechanic
  • Expert
  • 551 posts

You're welcome

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Thursday, September 22nd, 2011 AT 10:57 PM
  • Tiny
  • thefiretech
  • Member

Aside from pulling the tire and looking for/at the speed sensor, how can I tell which one I need. There seem to be two types for two different model tranny. A 3 speed and a 4 speed. I think it's a 4 speed, by the number of shifts but not sure. How can I tell the difference?
Thanks

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Friday, September 23rd, 2011 AT 2:07 PM
  • Tiny
  • promechanic
  • Expert
  • 551 posts

Probably the best thing to do is determine what transmission you have. You can check the transmission for a tag or sometimes it will say on the pan. You might have to take a picture of the shape of the transmission pan and look it up online. Or you can post it here and I can find it for you.

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Friday, September 23rd, 2011 AT 7:35 PM
  • Tiny
  • thefiretech
  • Member

Hello: I snapped these pics of the transmission. I was working on another issue-lots of water, from under the car, from the a/c even after being parked and some water on the passenger side on the floor after it rains. Seems that the drain tube was clogged. (I hope that was the problem.)
But I digress-
I believe I saw the VSS. Looks like the images on the web. The connector looks like it's wet from an oil leak somewhere. The VSS is right below and a little to the left of what looks like the oil(?) Pressure sensor-possibly. So I am pretty sure that it is a 4T60E Transmission. What I am amazed is the price range for the VSS-$190 (dealer) to $32.00. WoW!
Question: Does the ECM use the readings from the VSS for anything? Would the erratic readings affect control system and possibly effect millage?

Thanks Al

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Monday, September 26th, 2011 AT 6:18 PM
  • Tiny
  • promechanic
  • Expert
  • 551 posts

I think you are right about the transmission. It's hard to tell, but that is what it looks like.
I'm not sure on your car because it is older, but most of the time the computer does use the VSS for calculations. It probably doesn't use that reading for much though on your car because it was fairly new technology back then.

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Monday, September 26th, 2011 AT 7:17 PM

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