2005 Cadillac CTS • 6 cylinder 2WD Automatic •

When I fill my car with gas the DIC displays the estimated amount of miles that it can have with the gas was put in, but for some reason the miles range changes significantly lower with only the passing of a few miles. I.E. The DIC would read 186 miles range, then after driving for about 3 to 4 miles it would read 96 miles range. Why would this be? I've recently had the ECM re-programmed by the dealer but I have had a check engine light reading that shows the catalytic converter being faulty and I also have custom wheels if that would make any difference.
July 11, 2011.

This will be still a problem with the ECM, I would take it back and explain the problem, they may be able to do a re flash to fix the problem.

Jul 11, 2011.
The custome wheels should not make a difference on the range. What is the accuracy of the fuel gauge itself? There are some issues with fuel transfer from saddle to saddle, affecting fuel remaining, and therefore affecting range.

Jul 11, 2011.