For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC P0101: Mass Air Flow (MAF) Sensor Performance
DTC P1101: Intake Air Flow System Performance

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
Ignition 1 Voltage | P0030, P0036, P0102, P0443 | P0101 | P0102 | -- | P0101, P0103
MAF Sensor Signal | P0102 | P0102 | P0102 | P0102 | P0101, P0103, P1101
Ground | -- | P0102 | P0102 | -- | P0102

### Typical Scan Tool Data

#### MAF Sensor

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine Running Parameter Normal Range: 1,700-9,500 Hz
Ignition 1 Voltage | 0 Hz | 0 Hz | --
MAF Sensor Signal | 0 Hz | 0 Hz | 0 Hz
Ground | -- | 0 Hz | --

### Circuit Description

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 throttle model describes the flow through the throttle body and is used to estimate the MAF through the throttle body as a function of barometric pressure (BARO), TP, intake air temperature (IAT), and estimated MAP. The information from this model is displayed on the scan tool as the MAF Performance Test parameter.

• | The first intake manifold model describes the intake manifold and is used to estimate MAP as a function of the MAF into the manifold from the throttle body and the MAF out of the manifold caused by engine pumping. The flow into the manifold from the throttle uses the MAF estimate calculated from the above throttle model. The information from this model is displayed on the scan tool as the MAP Performance Test 1 parameter.

• | The second intake manifold model is identical to the first intake manifold model except that the MAF sensor measurement is used instead of the throttle model estimate for the throttle air input. The information from this model is displayed on the scan tool as the MAP Performance Test 2 parameter.

• | The fourth model is created from the combination and additional calculations of the throttle model and the first intake manifold model. The information from this model is displayed on the scan tool as the TP Performance Test parameter.

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.

#### Scan Tool Diagnostic Test Results

MAF Performance Test | MAP Performance Test 1 | MAP Performance Test 2 | TP Performance Test | DTCs Passed | DTCs Failed
--- | --- | --- | --- | --- | ---
-- | -- | OK | OK | P0101, P0106, P0121, P1101 | None
OK | OK | Fault | OK | P0101, P0106, P0121, P1101 | None
Fault | OK | Fault | OK | P0106, P0121, P1101 | P0101
OK | Fault | Fault | OK | P0101, P0121, P1101 | P0106
Fault | Fault | Fault | OK | P0121, P1101 | P0101, P0106
-- | -- | OK | Fault | P0101, P0106, P1101 | P0121
OK | OK | Fault | Fault | P0101, P0106, P0121, P1101 | None
Fault | OK | Fault | Fault | P0101, P0106, P0121 | P1101
-- | Fault | Fault | Fault | P0101, P0106, P0121 | P1101

### Conditions for Running the DTCs

• | DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0128, P0335, P0336 are not set.

• | The engine speed is between 400-8,192 RPM.

• | The IAT Sensor parameter is between -7 to +125°C (+19 to +257°F).

• | The ECT Sensor parameter is between 70-125°C (158-257°F).

• | This DTC runs continuously within the enabling conditions.

### Conditions for Setting the DTCs

The ECM detects that the actual measured airflow from MAF, MAP, and TP is not within range of the calculated airflow that is derived from the system of models for more than 2 seconds.

### Action Taken When the DTC Sets

DTCs P0101 and P1101 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0101 and P1101 are Type B DTCs.

### Diagnostic Aids

• | A steady or intermittent high resistance of 15 ohms or greater on the ignition 1 voltage circuit will cause the MAF sensor signal to be increased by as much as 60 g/s. To pinpoint this condition perform a voltage drop test on the circuit.

• | Any type of contamination on the MAF sensor heating elements will degrade the proper operation of the sensor. Certain types of contaminants act as a heat insulator, which will impair the response of the sensor to airflow changes. Water or snow can create the opposite effect, and cause the signal to increase rapidly.

• | Depending on the current ambient temperature, and the vehicle operating conditions, a MAF sensor signal circuit that is shorted to the IAT signal circuit will increase or decrease the MAF sensor signal that is interpreted by the ECM. Additionally it may cause a rapid fluctuation in the IAT Sensor parameter.

• | A skewed or stuck engine coolant temperature (ECT) or IAT sensor will cause the calculated models to be inaccurate and may cause this DTC to run when it should not. Refer to Temperature Versus Resistance .

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Controls Connector End Views

• | Engine Control Module Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Output Controls

• | Scan Tool Snapshot Procedure

#### Special Tools Required

J 38522 Variable Signal Generator

### Circuit/System Verification

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 150 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 Altitude Versus Barometric Pressure .
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.

### Circuit/System Testing

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 leak

• | Water intrusion

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

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

### Component Testing

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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Mass Airflow Sensor/Intake Air Temperature Sensor Replacement

• | Control Module References for ECM replacement, setup, and programming