Pontiac Fiero 1988 Service Manual page 491

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6E2-A-36 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI)

M A T SENSOR

TO MAP SENSOR

' THIS WIRE MAY ALSO HAVE A TRACER COLOR

MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT

(LOWTEMPERATURE INDICATED)

2.5L "P" SERIES (TBI)

Circuit Description:

The manifold air temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM

applies a voltage (4-6 volts) on CKT 472 to the sensor. When manifold air is cold, the sensor (thermistor)

resistance is high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance

becomes less and the voltage drops.

Test Description:

Numbers below refer to circled

numbers on the diagnostic chart.

1. This step checks to see if Code 23 is the result of a

hard failure or, an intermittent condition.

A Code 23 will set if:

• Signal voltage indicates a MAT temperature

less than-30°C.

• Engine is running for longer than 58 seconds.

2. This test simulates conditions for a Code 25. If the

"Scan" tool displays a high temperature, the ECM

and wiring are OK.

3. This step checks continuity of CKTs 472 and 469.

If CKT 469 is open, there may also be a Code 33.

Diagnostic Aids:

If the engine has been allowed to cool to an

ambient temperature (overnight), coolant and MAT

temperatures may be checked with a "Scan" tool and

should read close to each other.

A Code 23 will result if CKTs 472 or 469 become

If Code 23 is intermittent, refer to Section "B".

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