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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 15201
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I own a 2006 chevy corvettec6. My speedometer is completely

Customer Question

Hi i own a 2006 chevy corvettec6. My speedometer is completely off. It starts by like3 mph and increases to almost10 mph the higher the speed. I had this same exact problem on my2001 chevy camaro. Please help
Submitted: 11 months ago.
Category: Chevy
Expert:  Jared D replied 11 months ago.

GM says that due to the nature of these speedometers there is a degree of variation that cannot be corrected. They say that 4 MPH off at 20 mph, 3 mph at 45 mph and 2 mph at 65 mph is acceptable. Would you say that yours is off more than that?

Customer: replied 11 months ago.
my speedometer is off by almost as much as10 mph at 60 mph
Expert:  Jared D replied 11 months ago.

Original tire size right? Does it say you are going faster or slower than you really are?

Customer: replied 11 months ago.
everything is absolutely stock and original size. My speedometer says 80mph when im actually only going72_73 mph
Expert:  Jared D replied 11 months ago.

Have you had it in to the dealer to see if there is a re-program that can be done? There is nothing listed on the GM database saying that they have identified a problem, but they could have something that they have not yet published.

Are you the original owner? You aren't using any kind of chip or programmers right?

Do you have a scan tool that will monitor the vehicle speed sensor?

Customer: replied 11 months ago.
but they just ran codes and nothing came up. No what is a scan tool
Expert:  Jared D replied 11 months ago.

A scan tool is used to run diagnosis on the vehicle. If there is a problem with the speedometer the scan tool will be the only way to tell for sure. It can pull up the signal from the vehicle's speed sensor and see if it matches with the speedometer. If the speed sensor is correct but the speedometer is off then you know the problem is in the speedometer.

Customer: replied 11 months ago.
everything matches I don't feel like I'm getting an answer at all I've tried everything you have already suggested
Expert:  Jared D replied 11 months ago.

Perhaps you could list all of the things you have tried so that I don't suggest them to you.

It's hard to know where you are in the diagnosis process without you telling me and it threw me off a little when you seem unfamiliar with terms such as "scan tool".

I can opt out and see if someone else is willing to help if you would like.

Customer: replied 11 months ago.
Sure maybe someone that has chevy corvette experience. Also remember your the expert and I shouldnt be familiar with your terms because I am not a mechanic like you sir
Customer: replied 11 months ago.
If I gave you my vin# ***** there be a way to check if work has been done to my car? I was just under it and it looks like the rear diff6has a cover platte that has been taken off. I can tell because the heads of the bolts have marks. That could be a start to my issue
Customer: replied 11 months ago.
Ok i have researced for hours looks like my gears have been changed in my rear diff do i just have to get it calibrated to the correct ratio?
Expert:  Jared D replied 11 months ago.

Sorry, they dropped your question to my timed out list for some reason and I didn't see your responses.

You should be able to have the dealership reprogram the PCM to match the gear ratio in the differential. They will need to know the ratio- do you have the info on what gearset was put in there?