Does anyone know the option code for the rear-end ratio for a 2000 C5? I recently changed rear tires to a 295-35-18 and my speedometer is registering an incorrect MPH. When I am going 60, my speedo is registering a much slower speed. I have a Predator hand-held and have re-programmed the computer to the correct tire size, but I must have a different rear-end ratio other than 2:73. I think there were two options for different rear-ends, a 3:15 and a 3:43 but cannot decipher which code this would be. I think all of the option codes are listed on a sticky tag inside the glove box. Thanks Mike F.
Was it something I said, or does no one out there know the answer????? Come on folks!!! I really need to know before I get another speeding ticket.

 

The gear ratio on a C5 will not affect the speedo. It's on the output side of the differential, so it only measures halfshaft RPM, not tranny output RPM like an F-body. If you have an A4 and change gears, you will have to program it, but only to adjust shift points, as some are MPH based. If you have an A4, look for RPO Code G90. This indicates the optional 3.15 rearend.

This is strictly word of mouth, but the gear selection on the Predator and other handhelds is supposedly a remanent of F-body programming, and changing it will give you the problems you are having. The only parameter you should change is tire size. Just what I've heard on CF and DC. I have an MN6 and don't have to worry.

 

I checked and I do have the 3:15 rear end. When I originally down loaded the info into the Predator, it showed me having a 3:43. I did reprogram it to a 2.73. Originally the speedo was registering a speed faster than I was really going, so I reprogrammed it to a 2:73. The scary thing is that over a period of 40-50,000 miles if the original programming was wrong, that would mean a higher mileage than actually driven. That would mean my warranty would expire about 6700 miles sooner than actual, and not to mention the value decline that is associated with mileage. I wonder if anybody really checks this crap out. Is GM pulling some kind of scam? Who knows. I will reset the correct parameters and see what happens, but I do want to thank you for your reply. It should point me in the right direction. Thanks Mike Fesi