Mercury Mountaineer 2005 - Manual (Page 250)

Transmission/Transaxle code designations
You can find a transmission/transaxle code on the vehicle certification
label. The following table tells you which transmission or transaxle each
code represents.
Code Description
A CVT (continuously variable transaxle)
B Six-speed automatic (Aisin F21)
2005 Montego (mgo)
Owners Guide (post-2002-fmt)
USA_English (fus)
Maintenance and Specifications
250