Inaccurate spedometer

90 Chevy Lumina Euro Sedan speedometer reads 20-25 miles high. The unit on the transaxle that sends speed info was replaced no help. Any suggestions? The manual shows the instrument cluster & EEC in the circuit also.

Are you saying the speedo reads 25 MPH when the car is not moving? Or that it reads 25 MPH high at a particular speed? If the latter, does it jump to 25 MPH too high as soon as you start rolling, or is it a sliding scale, like 5 MPH too high at 10 MPH, 10 MPH too high at 15 MPH, etc?

Not to give you any false hope, as I don’t have an answer for any of these conditions. I’m just curious and figure the answers to these questions may give some clues to somebody who does have an answer.


Russ i believe the speedometer reads hi thru out its range while car is moving. For instance everyone else is doing 60 my speedo reads 80-90 mph. At 40 it will read 60 or so. As i stated the unit on the transaxle[forget name]that sends speed info was replaced no help. 90 Chevy Lumina Euro Sedan.

did this do this same 20 mph higher with the old speed sensor?

is it the same mph difference all the way up, or does the difference increase with more speed?

that sounds like a metric /english problem.

are you sure the cluster doesnt have a way to switch between mph and kph???

does your speed dial on the dash have both sets of numbers? if it only has one set i’ll bet there is a connection between the MPH and KPH selector.

Are you sure this is not a metric/English combined unit? I rented a Ford recently and you could flip back and forth between kilometers and miles/hr; 50 mph is 80 km/hr, 40 mph is 64 km/hr.