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The barometric pressure (BARO)
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The manifold absolute pressure (MAP)
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The intake air temperature (IAT)
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The engine RPM
P0121
The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.
Circuit/System Testing
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Inspect thoroughly for any type of leak or restriction
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Air leaks at throttle body mounting area and intake manifold sealing surfaces
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Throttle body for dirt, debris, and coking--Refer to Throttle Body Cleaning.
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Increase the engine speed slowly to 3,000 RPM, then back to idle.
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Exit from the snapshot and review the data.
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Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.
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If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle, refer to DTC P0101 or P1101.
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Broken throttle shaft
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Any throttle body damage
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If any of these conditions exist, replace the throttle body assembly.
Operation
The Mass Air Flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Electronic Control Module (ECM) uses the MAF sensor signal to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle condition. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has the following circuits:
An ignition 1 voltage circuit
A ground circuit
A MAF sensor signal circuit
An IAT sensor signal circuit
A low reference circuit
The ECM applies 5 volts to the MAF sensor on the MAF sensor signal circuit. The sensor uses the voltage to produce a frequency based on the inlet air flow through the sensor bore. The frequency varies in a range of near 1,700 Hertz at idle to near 9,500 Hertz at maximum engine load.
Removal & Installation
Fig. Remove the 2 bracket mounting bolts
Testing
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