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 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 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. |
| • | A fourth model is created from the combination and additional calculations of the throttle model and the first intake manifold model. |
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.
Throttle Model | First Intake Manifold Model | Second Intake Manifold Model | Fourth Model | DTCs Passed | DTCs Failed |
X | X | Pass | Pass | P0101 P0106 P0121 P1101 | None |
Pass | Pass | Failed | Pass | P0101 P0106 P0121 P1101 | None |
Failed | Pass | Failed | Pass | P0106 P0121 P1101 | P0101 |
Pass | Failed | Failed | Pass | P0101 P0121 P1101 | P0106 |
Failed | Failed | Failed | Pass | P0121 P1101 | P0101 P0106 |
X | X | Pass | Failed | P0101 P0106 P1101 | P0121 |
Pass | Pass | Failed | Failed | P0101 P0106 P0121 P1101 | None |
Failed | Pass | Failed | Failed | P0101 P0106 P0121 | P1101 |
X | Failed | Failed | Failed | P0101 P0106 P0121 | P1101 |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0101 Mass Air Flow (MAF) Sensor Performance
Conditions for Running the DTC
| • | DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0335, P0336 are not set. |
| • | The engine speed is between 450-6,800 RPM. |
| • | The IAT Sensor parameter is between -7°C and +125°C (19-257°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 DTC
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 0.5 second.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
| • | Inspect the harness of the mass air flow (MAF) sensor to verify that it is not routed too close to the following components: |
| - | The secondary ignition wires or coils |
| - | Any solenoids |
| - | Any relays |
| - | Any motors |
| • | A low minimum air rate through the sensor bore at idle or during deceleration may cause this DTC to set. Inspect for the following conditions: |
| - | Any deposits on the throttle plate or in the throttle bore |
| - | Any vacuum leak downstream of the MAF sensor |
| • | Inspect for any contamination or debris on the sensing elements of the MAF sensor. |
| • | Inspect the air induction system for any water intrusion. Any water that reaches the MAF sensor will skew the sensor and may cause this DTC to set. |
| • | A wide open throttle acceleration from a stop should cause the MAF sensor parameter on the scan tool to increase rapidly. This increase should be from 5-12 g/s at idle to 200 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system. |
| • | Inspect for a skewed or stuck ECT sensor. |
| • | A high resistance of 15 ohms or more on the ignition 1 voltage circuit may cause the DTC to set. A high resistance may cause a driveability concern before this DTC sets. |
| • | The barometric pressure that is used to calculate the predicted mass air flow value is initially based on the manifold absolute pressure (MAP) sensor at key ON. When the engine is running the BARO value is continually updated near wide open throttle. A skewed MAP sensor will cause the calculated mass air flow value to be inaccurate and may result in a no start condition. The value shown for the MAP sensor parameter varies with the altitude. With the ignition ON and the engine OFF, 101 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude. |
| • | A high resistance on the low reference circuit of the MAP sensor may cause this DTC to set. |
| • | A short to voltage on the 5-volt reference circuit of the MAP sensor may cause this DTC to set. |
If the condition is intermittent, refer to Testing for Intermittent Conditions and Poor Connections .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step will determine if the manifold absolute pressure (MAP) sensor pressure is within the proper range for a given altitude.
-
This step will determine if the MAP sensor voltage is within the proper range at idle.
-
This step will determine if the MAP sensor responds properly to the change in manifold pressure.
-
This step will determine if the throttle position (TP) sensors are operating properly.
-
This step will determine if any mechanical faults have caused this DTC to set.
-
This voltage drop will determine if high resistance has caused this DTC to set.
Step | Action | Values | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||||||||||||||
2 | Attempt to start the engine. Does the engine start? | -- | Go to Step 3 | Go to Step 5 | ||||||||||||||||||||
3 | Observe the Diagnostic Trouble Code (DTC) Information with the scan tool. Does the scan tool display any DTCs set other than DTC P0068 or DTC P0101? | -- | Go to Step 4 | |||||||||||||||||||||
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Diagnostic Aids | ||||||||||||||||||||
|
Important:: The Altitude vs. Barometric Pressure table indicates a pressure range for a given altitude under normal weather conditions. Weather conditions consisting of very low or very high pressure and/or temperature may cause a reading to be slightly out of range.
Is the MAP sensor pressure within the specified range, as indicated on the altitude vs. barometric pressure table? | -- | Go to Step 6 | Go to DTC P0106 | |||||||||||||||||||||
Does the MAP sensor parameter decrease? | -- | Go to Step 7 | Go to DTC P0106 | |||||||||||||||||||||
Does the MAP sensor parameter change smoothly and gradually through the specified range of the test? | -- | Go to Step 8 | Go to DTC P0106 | |||||||||||||||||||||
Is the TP indicated angle parameter within the specified range? | 95-100% | Go to Step 9 | Go to DTC P0120 | |||||||||||||||||||||
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 | |||||||||||||||||||||
Is the voltage within 0.50 volts of the specified value? | B+ | Go to Step 11 | Go to Step 12 | |||||||||||||||||||||
11 | Test for an intermittent and for a poor connection at the mass air flow (MAF) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 | ||||||||||||||||||||
12 | Repair the high resistance in the ignition 1 voltage circuit of the mass air flow (MAF) sensor. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||||||||||||||
13 | Replace the mass air flow (MAF)/intake air temperature (IAT) sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- | ||||||||||||||||||||
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 | ||||||||||||||||||||
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||||||||
