One problem related to transmission solenoid has been reported for the 2006 Mazda MAZDA6. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2006 Mazda MAZDA6 based on all problems reported for the 2006 MAZDA6.
While driving 65 mph down the interstate, my 2006 Mazda 6 made a loud noise like grinding gears and stalled for a second reved up and went into 3rd gear. The car went from 65 mph to almost a stop and then to 20 mph in the middle of the interstate. After that, the car downshifted several times in the next couple of days. Research showed many other 2006 Mazda 6 owners with similar problems. A Mazda TSB was posted in December 2006, and the car was purchased in November 2006. Mazda has not notified any costomers of this problem and a transmission going out at 58k is not typical. The dealer said it was the valve body solenoids. Replaced those for $800 and still shifted out of gear. Then paid $3800 for a new transmission that might do the same thing in a few thousand miles. If you are out of warrany, Mazda does nothing for you. This is a very serious rear end collision hazard.