Shift Light: Testing and Inspection

Chart C-8B:

Shift Light Circuit:

CIRCUIT DESCRIPTION:
The shift light indicates the best transmission shift point for maximum fuel economy. The light is controlled by the ECM and is energized by grounding circuit 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).
^ Engine Speed.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. When the ignition is "ON" and the engine is "OFF," the shift light should be "OFF." If the light is "ON," there is a short to ground in CKT 456 or a fault in the ECM.

2. When the diagnostic terminal is grounded, the ECM should ground circuit 456. This should turn "ON" the shift light.

3. This checks the shift light circuit up to the ECM connector. If the shift light illuminates, then the ECM does not have the ability to ground the circuit.