Erratic speedometer

THEFIRETECH

MEMBER
1993 CHEVROLET LUMINA
144,000 MILES

Hello
My speedometer is behaving erratically. 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.

11 Replies

PROMECHANIC

MECHANIC
536 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 10:57 PM

THEFIRETECH

MEMBER
7 POSTS

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

PROMECHANIC

MECHANIC
536 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

THEFIRETECH

MEMBER
7 POSTS

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

PROMECHANIC

MECHANIC
536 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

HYELINE

MEMBER
10 POSTS

Hello all, I found this thread online and it seems helpful. I have a 1993 Lumina 3 speed and changed the VSS based on this advice. It did not solve the problem. What else can I try?

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Monday, February 8th, 2021 AT 10:08 AM

KEN L

MASTER CERTIFIED MECHANIC
42,878 POSTS

This sounds like the cluster is going out. here is a video of the job being done on a similar car:

https://youtu.be/_HEC44xENxw

Please run down this guide and report back.

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Wednesday, February 10th, 2021 AT 10:37 AM