Chart C-8B Manual Transmission (M/T) Shift Light Check

Chart C-8B:

ECM Wiring Diagram (Part 4 Of 4):

CIRCUIT DESCRIPTION:
The shift light indicates the best transaxle shift point for maximum fuel economy. The 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:

^ Engine Coolant Temperature (ECT) sensor.
^ Throttle Position (TP) sensor.
^ Vehicle Speed Sensor (VSS).
^ Engine speed Crankshaft Position (CKP) sensor.

The ECM uses the measured RPM and the vehicle speed to calculate what gear the vehicle is in. It's this calculation that determines when the shift light should be turned "ON."

TEST DESCRIPTION: Number(s) below refer to circled number(s) 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 "test" terminal is grounded, the ECM should ground CKT 456 and the shift light should come "ON."
3. This checks the shift light circuit up to the ECM connector. If the shift light illuminates, then the ECM connector is faulty or the ECM does not have the ability to ground the circuit.