Here is a diagram which shows the location of various solenoids (PCS, TCC-PWM and Shift) located in a 4T65E transmission, the vehicle speed sensor (VSS) and other components. These are mainly located under the side cover assembly (left hand side). Also, applicable to L67 equipped GM cars with the 4T65E-HD autotransaxle.
Refer to the SPID label located on the back of the trunk lid, spare tire cover or doors for which autotransaxle your Buick has. GM RPO codes are as follows:
MN3 - 4T65E
M15 - 4T65E
MN7 - 4T65E-HD
M13 - 4T60E
EPC- Pressure Control Solenoid (PCS)
Applicable to all Buicks with the 4T65E autotransaxle. Some is applicable to Buicks with the 4T60E, GM RPO code M13 and can be used as a reference.