Pontiac Fiero 1988 Service Manual page 467

6 E 2 - A - 1 2 D R I V E A B I L I T Y A N D E M I S S I O N S - F U E L I N J E C T I O N ( T B I )
I.P. HARNESS CONNECTOR
15 WAY. (FRONT VIEW)
ECM
fl
S
«-
ORN 240
ORN 240
W10
W15
FUSIBLE LINK
ECM FUSE
TO INJECTOR
•
BATTERY
IGNITION
SWITCH
GAGE FUSE SES LIGHT
DIAGNOSTIC TEST
ALDL CONNECTOR
B
M
4 PNK7BLK 439
BRN/WHT419
WHT/BLK451 —
450
BLK/WHT
ENGINE
GROUND
ORN 461
W16
B22
B15
W12
B1
KEEP ALIVE
MEMORY (12V)
IGN 12V
5 6V
SERIAL DATA
4-30-87
15-WAY I.P. CONN.
7S 3272-6E
4-9-87
CH AIT A-2
NO ALDL DATA OR W O N T FLASH CODE 12
"SERVICE ENGINE SOON" LIGHT ON STEADY
2.5L " P " SERIES (TBI)-
Circuit Description:
There should always be a steady "Service Engine Soon" Light, when the ignition is "ON" and engine
stopped. Battery is supplied directly to the light bulb. The electronic control module (ECM) will turn the light
"ON" by grounding CKT 419 at the ECM.
With the diagnostic terminal grounded, the light should flash a Code 12, followed by any trouble code(s)
stored in memory.
A steady light suggests a short to ground in the light control CKT 419, or an open in diagnostic CKT 451.
Test Description:
Numbers below refer to circled
numbers on the diagnostic chart.
1. If there is a problem with the ECM that causes a
"Scan" tool to not read Serial data, then the ECM
should not flash a Code 12. If Code 12 does flash,
be sure that the "Scan" tool is working properly on
another vehicle. If the "Scan" is functioning
properly and CKT 461 is OK, the PROM or ECM
may be at fault for the No ALDL symptom.
2. If the light goes "OFF", when the ECM connector
is disconnected, then CKT 419 is not shorted to
ground.
3. This step will check for an open diagnostic CKT
451.
4. At this point, the "Service Engine Soon" light
wiring is OK. The problem is a faulty ECM or
PROM. If Code 12 does not flash, the ECM should
be replaced using the original PROM. Replace the
PROM only after trying an ECM, as a defective
PROM is an unlikely cause of the problem.