One problem related to transmission failure has been reported for the 2005 Mercury Mountaineer. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2005 Mercury Mountaineer based on all problems reported for the 2005 Mountaineer.
Extremely hard shifting into reverse. Slipping in 3rd gear when transmission is running for 15 minutes. Over drive light flashes and transmission fails to work while on highway. I have to shift into neutral turn the car off then back on (while at 65mph) then it works fine the rest of the day.