Transmission Control Systems: Description and Operation

1 - 4 Upshift Circuit:

Purpose:
The 1-4 upshift system requires the vehicle to be shifted from first gear to fourth gear. When in operation it is not possible to shift into second or third gears. By locking out gears during specified engine conditions, fuel economy is increased.

Operation:
The ECM uses engine speed, vehicle speed, throttle position and engine coolant temperature sensors to determine if the vehicle is within parameters to shift directly to fourth gear while it is in first gear. The ECM completes a ground path to the 1-4 upshift relay under the following conditions:

^ Engine running
^ Vehicle speed greater than 12 mph but less than 19 mph
^ Engine speed less than 1200 rpm
^ Throttle position less than 35%
^ Engine coolant temperature greater than 50°C (122°F)


Location:
The 1-4 upshift relay is mounted on the left front wheel housing near the battery. The 1-4 upshift solenoid is located in the transmission shift linkage.