Intro - First Offical Post (Recent replaced 98 Yukon with a 17)

[RobH]

The original issue transmission thermal bypass valve (thermostat) for the MYC (6l80E) and MYD (6L90E) transmissions maintains the transmission fluid at around 185F. The Service Bulletin No.: 21-NA-199 (search online for the current version) calls for installing a 70C/158F Thermal Bypass Valve to keep the transmission cooler. You may not have one of these two six speed transmissions.

 

[RobH]

Further to my last, there should be a SERVICE PARTS IDENTIFICATION (SPID) sticker on your glove box door. It lists the three character codes for Factory installed equipment. The code for the 6L80E transmission is MYC.

6 speeds
L Longitudinal/RWD orientation
80 - power handling rating
E - controlled by Electronic Control Module.

You can take your VIN to a GM dealership parts counter and get a listing of what all the three character codes mean.

Thank you for your service. Rob H

 

[Fless]

The code for the 6L80E transmission is MCY.

MCY? Or MYC?

 

[RobH]

MCY? Or MYC?

You may have caught me in the midst of correcting my error. Thank you. The correct code for the 6L80E is MYC. MYC, darn it. My fingers like to mis-type the characters.

MYC like on my SPID picture above. ^^^