Report: Smog Check Failure Due to Excessive Carbon Buildup
Cadillac DeVille Problem
Average Mileage: 135,500 mi (113,000 mi - 158,000 mi)
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.
Visitor, 1994 Cadillac DeVille, 158,000 mi
Caddy failed due to NOx being too high on both high and low speed tests
Car failed for high nox