P0100

Schematic:

CIRCUIT DESCRIPTION
The Mass Air Flow (MAF) sensor used on this vehicle is a hot film type and is used to measure the air flow rate. The MAF output voltage is a function of the current required to keep the air flow sensing element at a fixed temperature. The air flowing through the sensor cools the sensing element. The amount of cooling is proportional to the amount of the air flow. As the air flow increases, more current is required in order to maintain the hot film at a constant temperature. The MAF sensor converts the changes in current to a voltage signal read by the Engine Control Module (ECM). The ECM calculates the air flow based on this signal.

The MAF sensor uses the following circuits to operate:
^ Switched battery voltage
^ 5 volt reference
^ Reference ground
^ Signal

The switched battery voltage is supplied from the engine controls power relay. The 5 volt reference for the mass air flow sensor is supplied from the same source in the ECM as the 5 volt reference for Accelerator Pedal Position (APP) sensor 1 and the Fuel Tank Pressure (FTP) sensor. The 5 volt reference voltage for each of the sensors is supplied on separate ECM terminals, but the terminals are connected internally to the shared voltage supply. The reference ground circuit is shared with the following components:
^ Camshaft Position (CMP) sensor
^ Intake Air Temperature (IAT) sensor
^ Engine Coolant Temperature (ECT) sensor
^ Throttle position (TP) sensor 1
^ Throttle position (TP) sensor 2

The ECM monitors the MAF sensor signal voltage and can determine if the sensor signal voltage is too low, too high, not indicating the expected airflow for a given operating condition, or that the signal appears to be stuck based on the lack of normal signal fluctuations expected during engine operation.

CONDITIONS FOR RUNNING THE DTC
- The battery voltage is more than 11 volts.
- One or both of the following DTCs are not set:
P1120, or P1220.
- The engine speed is more than 500 RPM.

CONDITIONS FOR SETTING THE DTC
The MAF signal indicates an airflow outside of a calculated range for a given RPM for at least 0.1 second.

ACTION TAKEN WHEN THE DTC SETS
^ The ECM illuminates the Malfunction Indicator Lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.
^ The ECM will calculate the airflow from the other sensor inputs.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes.
^ A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.
^ The ECM battery voltage is interrupted.
^ The scan tool clears the MIL/DTC.

TEST DESCRIPTION

Steps 1 - 7:

Steps 8 - 14:

Steps 15 - 21:

Steps 22 - 33:

Steps 34 - 36:

The numbers below refer to the step numbers on the diagnostic table.
7. The engine must remain running in order for the MAF display on the scan tool to update.
11. The ECM provides the reference ground for the MAF sensor. A small amount of voltage will appear on this circuit when the ECM is operational. The measured resistance of the circuit will increase when the ECM is operational. This is considered normal.
15. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. Disconnecting the APP connector will determine if the APP sensor is affecting the 5 volt reference circuit for the MAF sensor.
16. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. Disconnecting the fuel tank connector will isolate the FTP sensor and the fuel tank harness from the remainder of the circuit.
21. Disconnecting the ECM C2 connector will prevent the engine controls power relay from operating. When checking for a short to voltage on an ECM circuit, this relay should be energized. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected inside the ECM. A short to voltage on the 5 volt reference circuit of the APP 1 sensor will affect the operation of the MAF sensor.
22. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. A short to ground on the 5 volt reference circuit of the APP 1 sensor will affect the operation of the MAF sensor.
23. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. A short to ground on the 5 volt reference circuit of the FTP sensor will affect the operation of the MAF sensor.
25. The 5 volt reference for the APP sensor 1 and the FTP sensor are connected to the same source inside the ECM as the MAF sensor. A short to voltage on the 5 volt reference circuit of the FTP sensor will affect the operation of the MAF sensor.