Shift Light: Description and Operation

M/T Shift Light Circuit:

The shift light indicates the best transmission shift point for maximum fuel economy. The shift light is controlled by the ECM and is turned on by grounding CKT 456.

The ECM uses information from the following inputs to control the shift light:

^ Coolant Temperature Sensor (CTS)
^ Throttle Position Sensor (TPS)
^ Vehicle Speed Sensor (VSS)
^ RPM

The ECM uses the measured rpm and the vehicle speed to calculate what gear the vehicle is in. It is this calculation that determines when the shift light should be turned on.