Pontiac Fiero 1988 Service Manual page 497

6E2-A-42 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI)
MANIFOLD
ABSOLUTE
PRESSURE
(VACUUM)
5 6-87
M A P SENSOR
H]
A B C
lis
E C M
TO TPS
SENSOR
416 GRY
432 LT. GRN
T
469 BLK
TO MAT
SENSOR
W11
^J\^—
5 V REF
B20
MAP SIGNAL
W14
I
SENSOR
— GROUND
' THIS WIRE M A Y ALSO HAVE A TRACER COLOR
4-21-87
• 7S 3208-6E
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Bam
mjr mm?
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL VOLTAGE HIGH - LOW VACUUM)
2.SL SERIES (TBI)
Circuit Description:
The manifold absolute pressure sensor (MAP) responds to changes in manifold pressure (vacuum). The
ECM receives this information as a signal voltage that will vary from about 1 to 1.5 volts, at closed throttle idle,
to 4-4.5 volts at wide open throttle (low vacuum).
If the MAP sensor fails, the ECM will sustitute a fixed MAP value and use the throttle position sensor (TPS)
to control fuel delivery.
Test Description:
Numbers below refer to circled
numbers on the diagnostic chart.
1. This step will determine if Code 33 is the result of
a hard failure or an intermittent condition.
A Code 33 will set if:
• MAP signal voltage is too high (low vacuum).
• TPS less than 4%.
• These conditions for a time longer than 48
seconds.
2. This step simulates conditions for a Code 34. If the
ECM recognizes the change, the ECM, and CKTs
416 and 432 are OK. If CKT 469 is open, there
may also be a stored Code 23.
D i a g n o s t i c A i d s :
With the ignition "ON", and the engine stopped,
the manifold pressure is equal to atmospheric
pressure and the signal voltage will be high. This
information is used by the ECM as an indication of
vehicle altitude and is referred to as BARO.
Comparison of the BARO reading with a known good
vehicle with the same sensor is a good way to check
accuracy of a "suspect" sensor. Readings should be the
same ± .4 volt.
A Code 33 will result if CKT 469 is open, or if CKT
432 is shorted to voltage or to CKT 416.
If Code 33 is intermittent, refer to Section "B".