Smog Check Failure Due to Excessive Carbon Buildup on Cadillac DeVille

Problem Description and Possible Solution

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.

Problem Data
RepairPal Verified
Average mileage: 135,500 (113,000–158,000)
5 model years affected: 1991, 1992, 1993, 1994, more1995
8 people reported this problem
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Caddy failed due to NOx being too high on both high and low speed tests
Car failed for high nox