Shift Solenoid Relay: Description and Operation

Overdrive Switch:

UPSHIFT RELAY

This upshift relay is located under the battery near the frame rail in the engine compartment. The ECM uses engine speed, vehicle speed, throttle position, and engine coolant temperature to determine when the vehicle is in 1st gear. The ECM provides a ground path which energizes the relay when the vehicle should be shifted from 1st to 4th gear.


UPSHIFT SOLENOID

The 1-4 upshift solenoid is located in the transmission linkage. When the 1-4 upshift relay is energized, it activates the 1-4 solenoid which mechanically locks-out the transmission from being shifted into 2nd or 3rd gear from 1st gear.