Speedometer reading wrong


Asked by Sep 10, 2013 at 12:59 PM about the 1994 Chevrolet Lumina 4 Dr STD Sedan

Question type: Maintenance & Repair

I am the one that put the 15" tires and rims on the std Lumina that had 14".  I did the tire size chart as suggested 195/75R14  205/75R15 and the speedometer should not read more than about 4 mph lower at 65mph.(would be 69mph)  So I must have another problem.  The speedometer actual reads higher than the speed I am going.  At lower speeds I am going about 6 mph slower and at higher speed I am going about 11 mph slower. (66mph on speedometer is 55 mph)  I checked this with a gps.  Would anyone have an idea why a speedometer would read higher than actual speed?

9 Answers


I would put the 14s back on and recheck that, if it is still the same then it is posssible that the speed sensor is sending a unstable signal or the speedometer drive motor IC board is reading it incorrectly.

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The 14" tires and rims are gone. Would you know where the speed sensor is located and what it looks like. Thanks

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click on image, look on right side

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Thanks for the picture. Where can a guy get pictures like you sent DavidH25?

Google search whatever you are looking for. and when the search page come up on top click 'images' ....only thing is there are so many images, drawings, pictures that don't belong there you really should find the source of the image. That's what I did, when I found the image I went to the source to make sure it was a '94 Lumina before posting it

I found lots of pictures of the sensor, from parts suppliers, and have gotten my ass chewed on more than one occasion for posting copyrighted images...so of all the speed sensor pictures I found, every one has a watermark so that's why I didn't post a picture of the speed sensor it's self. I have to play by the rules


I replaced the speed sensor over the weekend and it did not make any difference. Does anyone have any other ideas? Also I apologize it shows the car as a 1994 and it is a 1993 if it makes any difference.


You may have to have an adapter made for your speedo to read correctly. Check around and see if any shops in your area do speedometer repair, they might be able to make you one, but it won't be cheap.


I thought I would let people know what I found. I went to a salvage yard and picked up an instrument cluster. I installed the cluster and the speedometer worked it read 2 mph lower just as expected with the 15” tires, but the odometer was not working. I decided to pull the whole cluster apart. I found that the odometer has a small circuit board that plugs into the main cluster board. The odometer board had a small burnt spot on it, I thought no big deal I will just put the odometer board from my original cluster in the salvage cluster. When I did the odometer worked but I ended up back with the original problem (At lower speeds I am going about 6 mph slower and at higher speed I am going about 11 mph slower. (66mph on speedometer is 55 mph). I went back to a salvage yard and got just the small odometer board out of a cluster and installed it in the original cluster from my daughter’s car. Everything worked fine!!! The odometer board had been sending false signals to the main board. Only one thing left was the speedometer reading 2 mph lower because of going from 14” to 15” tires. I went for a drive with the front plastic off the cluster, I pulled over and took the speedometer needle off with the car running and put it back on just a little above the stop pin. It took just a couple of tries but the speedometer is dead on at all speeds (verified with 2 gps units).

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