Shift Light: Description and Operation

In the L4 VIN 4 and V6 VIN T with Manual Transaxle, a bulb lights when the vehicle should be shifted to the next higher gear for better fuel economy. Battery voltage is applied to one side of the bulb. The other side of the bulb is switched to ground by the ECM, which uses engine data such as rpm, vehicle speed, and intake vacuum to compute an efficient shift point.