This powertrain control module (PCM) may develop a fault with its electrical ground location at the front of the engine block near the starter motor.
Problems for specific Cadillac DeVille years:
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Most reported 1992 Cadillac DeVille problems
The alternator may fail causing the battery to go dead, or an abnormal noise may develop. The dash warning light may or may not illuminate. A failed alternator will require replacement.
Excessive carbon build up in the engine combustion chambers may be the cause of a smog check failure due to excess NOx emissions. A "top engine" decoarbonization cleaning procedure will commonly correct this concern.