Pontiac Fiero 1988 Service Manual page 629

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6 E 3 - A - 4 6 D R I V A B I L I T Y A N D E M I S S I O N S

- FUEL INJECTION (PORT)

TO MAT SENSOR

— A / \ A / V V - - 5 V

THROTTLE BODY

" BACKUP SIGNAL

MANIFOLD A B S O L U T E PRESSURE (MAP) SENSOR CIRCUIT

(SIGNAL VOLTAGE LOW - HIGH VACUUM)

" P " SERIES (PORT)

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 1-1.5 volts at idle to 4-4.5 volts at

wide open throttle.

If the MAP sensor fails, the ECM will substitute 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. Code 34 will set when signal voltage is too low

(kPa less than 13) and ignition is turned "ON".

Engine running greater than 1200 rpm and

throttle open greater than 25%

2. If the ECM recognizes the high MAP signal, the

ECM and wiring are OK.

3. The "Scan" tool may not display 12 volts. The

important thing is that the ECM recognizes the

voltage as more than 4 volts, indicating that the

Diagnostic Aids:

An intermittent open in CKTs 432 or 416 will

result in a Code 34.

Ignition "ON" engine "OFF", voltages should be

within the values shown in the table on the chart.

Also CHART C-1D can be used to test MAP

Refer to "Intermittents" in Section "B".

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