The intake flow rationality diagnostic provides the within-range rationality check for the mass air flow (MAF), manifold absolute pressure (MAP), and the throttle position (TP) sensors. This is an explicit model-based diagnostic containing 4 separate models for the intake system.

The estimates of MAF and MAP obtained from this system of models and calculations are then compared to the actual measured values from the MAF, MAP, and the TP sensors and to each other to determine the appropriate DTC to fail. The following table illustrates the possible failure combinations and the resulting DTC or DTCs.

The engine control module (ECM) detects that the actual measured airflow from the MAF, MAP, and TP sensors is not within range of the calculated airflow that is derived from the system of models for more than 0.5 second.

DTCs P0101 and P1101 are Type B DTCs.

DTCs P0101 and P1101 are Type B DTCs.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 38522 Variable Signal Generator

1. If DTC P0641 or P0651 are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
2. Verify that restrictions do not exist in the exhaust system. Refer to Restricted Exhaust.
3. Engine running, observe the scan tool MAF Sensor parameter. The reading should be between 1,700-3,200 Hz depending on the ECT.
4. A wide open throttle (WOT) acceleration from a stop should cause the MAF Sensor parameter on the scan tool to increase rapidly. This increase should be from 2-6 g/s at idle to greater than 100 g/s at the time of the 1-2 shift.
5. The barometric pressure (BARO) that is used by the ECM to calculate the air flow models is initially based on the MAP sensor at ignition ON. When the engine is running, the ECM will continually update the BARO value near WOT using the MAP sensor and a calculation. A skewed MAP sensor will cause the BARO value to be inaccurate. Determine the current vehicle testing altitude. Ignition ON, observe the scan tool BARO sensor parameter. Compare the parameter to the Altitude vs Barometric Pressure table. Refer to Temperature Versus Resistance.
6. A skewed MAP sensor will also cause the first and second intake manifold models to disagree with the actual MAP sensor measurements. Use the scan tool and compare the MAP Sensor parameter to a known good vehicle, under various operating conditions.
7. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Verify the integrity of the entire air induction system by inspecting for the following conditions:

•	Any damaged components

•	Loose or improper installation

•	An air flow restriction

•	Any vacuum leaks

•	Water intrusion

•	In cold climates, inspect for any snow or ice buildup

2. Ignition OFF, disconnect the harness connector at the MAF/IAT sensor.
3. Ignition OFF for 90 seconds, test for less than 5 ohms between the ground circuit terminal C and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal B and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

5. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal A and ground.

⇒	If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

6. Connect the J 38522 to the vehicle. Refer to Component Testing for instructions.

To determine if the ECM can properly process the MAF sensor frequency signal, connect the J 38522 to the vehicle as follows:

1. Turn OFF the ignition.
2. Connect the battery voltage supply, and ground the black lead.
3. Connect the red lead to the signal circuit of the MAF sensor.
4. Set the duty cycle switch to Normal.
5. Set the Frequency switch to 5 K.
6. Set the signal switch to 5 volts.
7. Start the engine.
8. Observe the MAF Sensor parameter for the correct range of 4,950-5,025 Hz.

⇒	If the MAF Sensor parameter is not within the specified range, replace the ECM.

⇒	If the MAF Sensor parameter is within the specified range, replace the MAF sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.