Pontiac Fiero 1988 Service Manual page 567

6E2-C8-6 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI)
IGN
C G A G E
L *
INTRUMENT
PANEL
i.P. HARNESS CONNECTOR
15 W A Y . (FRONT VIEW)
39 PNK/BLK
«-
H
—«r-
15-WAY
I.P. CONN.
TAN/BLK 456 B7 -4T
SHIFT
LIGHT
CONTROL
5-1-87
* 7 S 3406-6E
4-21-87
CHART C-8B
MANUAL TRANSMISSION (M/T) SHIFT LIGHT CHECK
2.5L " P " SERIES (TBI)
Circuit Description: "
The shift indicates the best transmission 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:
• Coolant temperature
• TPS
• VSS
• R P M
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".
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.