One problem related to check engine light on has been reported for the 2004 Mazda MAZDA6. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Mazda MAZDA6 based on all problems reported for the 2004 MAZDA6.
Engine is throwing a rod, needs new engine, no check engine light or other warning lights present to alert to impending failure.