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1999 Cadillac DeVille
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58 Posts
Discussion Starter #1
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?
 

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1998 Seville STS / 2013 Chevrolet Impala
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1,889 Posts
It's the stereo. Those OBD-II northstar cars go nuts when you change out the radio without relocating the stock unit to the trunk.
 

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1995 SEDAN DEVILLE-4.9 & 1978 SEDAN DEVILLE-425
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1,673 Posts
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 radio_Others changing out their stock radios for others have posted here with much more extensive problems.
 

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1990 350 Brougham (The cruiser), 1988 Mark VII LSC (The DD)
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5,545 Posts
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.
 

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1999 Cadillac DeVille
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58 Posts
Discussion Starter #5
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.
 

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1990 350 Brougham (The cruiser), 1988 Mark VII LSC (The DD)
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5,545 Posts
Leave the factory radio in and disconnect the battery for about 10 minutes. Hook it back up and wait a little. That should clear the memory on the computers and reset stuff.
 
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