Pontiac Fiero 1988 Service Manual page 593

6E3-A-10 DRIVABILITY AMD EMISSIONS - FUEL INJECTION (PORT)
FUSIBLE LINK
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ORN 240
ORN 240
9 IGNITION
SWITCH
BATTERY
I. P.
CONNECTOR
E C M / I G N
GAGE SES LIGHT
FUSE
L
_ J
ALDL CONNECTOR
- PNK/BLK439
BRN/WHT419
ORN 461
o
v
E
B A
o
J
o
v
\
1 _
o
J
— WHT/BLK451
BLK/WHT " " J * 5 0
M
ENGINE
flQfcGROUND
C16
B1
A6
D1
ECM
BATTERY
BATTERY
12V. IGN
" SERIAL DATA
5-6 V
1
IAGNOSTIC TEST
TERMINAL
5-18-87
7-13-87
* 5 S 1 8 9 7 - 6 E
CHART A-2
NO ALDL DATA OR WON'T FLASH CODE 12
"SERVICE ENGINE SOON" LIGHT ON STEADY
2.8L "P" SERIES (PORT)
Circuit Description:
There should always be a steady "Service Engine Soon" Light when the ignition is "ON" and engine
stopped. Battery ignition voltage is supplied 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, the ECM
should not flash a Code 12. If Code 12 is flashing,
check for CKT 451 short to ground. 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, 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.