Shift Light: Description and Operation

Overdrive Switch:

UPSHIFT LIGHT

Whenever the ECM enables the 1-4 upshift system, the ECM provides a ground which turns "ON" the "ONE" to "FOUR" light. The "UPSHIFT" light and the "ONE" to FOUR" light will remain on until the transmission is placed in fourth gear, vehicle speed is less than 12 mph or greater than 19 mph or the ECM disables the 1-4 upshift system.




UPSHIFT RELAY

This upshift relay is located behind the battery on the cowl in the engine compartment. The ECM uses engine speed, vehicle speed, throttle position, and engine coolant temperature to determine if the vehicle is within the parameters to shift to 4th gear while 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 any other gear other than 4th gear from 1st gear.