OK when I first got my 99 Deville the mpg (top left on dash)worked how it should but after I hooded up an after market stereo and put back in the factory one the MPG flip flops around up and down really back what can be the problem?
Much of the electronics on the '94-'99 Devilles are all tied in through the stock radio system.You`re lucky if JUST your MPG avg acts up with your new radithers changing out their stock radios for others have posted here with much more extensive problems.
Definitely the radio. The radios on these cars cannot simply be changed out. They control much more than just the sound. You have to relocate the factory head unit into the trunk and then install a new head unit in the dash.
Oh no trust me I had more problems then this but I put my factory back in and now I have this problem still remaining so im I just stuck with this problem? Will its not really a problem but more irritating.