The Check Engine Light can illuminate with codes due to the lack of EGR (exhaust gas recirculation) flow caused by the intake manifold passage plugging up with carbon and oil. The EGR valve has to be removed and the passage cleaned thoroughly. Partial restriction of this passage can cause Smog test failures for the NOx emissions without causing a drivability symptom.
Check Engine Light on Due to Clogged EGR Passage in Intake Manifold on Mercury Cougar
Average mileage: 159,969 (122,338–194,000)
Exhaust & Emissions affected: 2.5L V6
16 people reported this problem
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Insufficient EGR flow upon diagnostics.
Not enough flow in EGR
EGR Valve Blown/hole in the valve
the egr valve needs replaced