The check engine light may come on due to failure of the Variable Camshaft Timing (VCT) solenoids. The VCT solenoids will need to be replaced if they are the reason the check engine light came on.Google+
Car Problem Reports
Mercury Mariner Check Engine Light Illumination
Mercury Mariner Problem
Engines Affected: 2.3L 4 Cylinder, 3.0L V6
Average Mileage: 45,777 mi (30,000 mi - 69,000 mi)
Visitor, 2009 Mercury Mariner, 3.0L V6, 48,945 mi
Check engine light came on and engine became sluggish as if there was no power.
Visitor, 2009 Mercury Mariner, 3.0L V6, 69,000 mi
Same problem as others. Engine light goes on and off several different times and finally stays on. AutoZone told me it was some kind of timing issue. Took to my mechanic and he verified it is this same issue with the cam timing. Repair? Estimate $350.00
Visitor, 2009 Mercury Mariner, 3.0L V6, 33,000 mi
Engine light comes on for a while then goes off for a while.Off and on .Now tire sensor is on,
Visitor, 2007 Mercury Mariner, 3.0L V6, 50,000 mi
Check engine light on and fwd light periodically
Visitor, 2010 Mercury Mariner, 3.0L V6, 35,000 mi
Engine light came on ANC dealership could not figure out why. When I tried to drive it the next day it started and said ok to drive but would not accelerate I tried for a couple minutes then restarted it and was hood to go. Makes me worried.