Chart C-8C Manual Trans. Shift Light Check

Chart C-8C:

Chart C-8C Wiring Diagram:

CIRCUIT DESCRIPTION:

The upshift light indicates the best transaxle shift point for maximum fuel economy, based on engine speed and load. The light is controlled by the ECM and is turned "ON" by grounding CKT 456.

The manual transmission shift light will be enabled while cruising down the highway and all the these conditions are met for 1 minute.

^ Coolant temperature must be above 50~C (122~F).
^ Vehicle speed is greater than 55 mph.
^ TPS greater than 3%.
^ Any gear other than 4th gear.
^ Engine speed above 1075 rpm.

The automatic transmission shift light will be enabled while cruising down the highway and all the these conditions are met for 30 seconds.

^ Coolant temperature must be above 50~C (122~F).
^ Vehicle speed is greater than 47 mph.
^ TPS greater than 0%.
^ Any gear other than 4th gear.
^ Engine speed above 1400 rpm.



The upshift light will also be turned "ON" if the engine rpm exceeds 5200 rpm in any gear other than 4th gear. The ECM uses the measured rpm and the vehicle speed to calculate what gear the vehicle is in. It is that calculation that determines when the shift light should be turned "ON".

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

1. This should not turn "ON" the shift light. If the light is "ON," there is a short to ground in CKT 456 wiring or a fault in the ECM.

2. When the diagnostic 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.

DIAGNOSTIC AIDS:

On early 1990 automatic transmissions equipped vehicles the upshift light will not work. These early built vehicles will have a LIGHT GREEN/BLACK wire between ECM terminals "A12" and cavity "G" of the 10 way instrument panel connector. However, there is no wire between cavity "G" of the 10 way instrument panel connector and terminal "B15" of the instrument panel connector. Later built 1990 automatic transmission equipped vehicles will have an operational upshift light as shown in the wiring diagram.