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2003 Cadillac DeVille Base 4dr Sedan

2003 Cadillac DeVille
Trim Info:
Front Wheel Drive, 4 Door Sedan, Full Size
18 mpg city / 27 mpg hwy
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July 31, 2012, 6:33 am


Question: Service engine soon light is always on

The service engine soon light has been on for 2 years now. The code indicates to change the cat. convertor. Well, I changed it twice but the light keeps coming back on. I was told to get a cad factory convertor from the dealer for $800. I need to inspect the car, any solutions?

August 4, 2012, 7:21 am

Ron W
Expert Mechanic

The aftermarket Cats could be the issue. But, sometimes the Cat efficiency codes are set by defectiveO2 sensors as well. It is difficult to isolate which one sets the codes, so most times I recommend replacing all of them in this type of situation.

The other thought I have is when the Cats were replaced , did anyone check your fuel system to make sure it was working correctly? If the car runs too lean or too rich for to long, it can damage a new cat and cause repeat failures.

When I replace Cats, I usually replace the O2s at the same time in most cases as it is cheap insurance that the Cat will survive and I make sure all tune up stuff is up to date.

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