How to Determine Which Line of GMC Sierra Transmission is Return Line

Question:

2014 GMC SIERRA WHICH COOLING LINE IS THE RETURN TO THE TRANSMISSION

asked by: AJ W

Expert Reply:

In order to tell which transmission fluid line is the return line leaving the factory cooler of a vehicle like your 2014 GMC Sierra you want to start with your vehicle cold. Start it up and put it in drive and brake torque it (apply brakes and rev the engine), for about 10 seconds or so, put vehicle back in park, and turn engine off.

Now quickly go out and feel both transmission lines. The cooler of the two is the return line and the one to use for installing the # D13503.

expert reply by: Jameson C