Circuit Description
The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The MAF sensor used on this vehicle is a hot film meter (HFM) type. The engine control module (ECM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. The MAF sensor signal 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 that is read by the ECM. The ECM calculates the air flow based on this voltage signal. The MAF sensor uses the following circuits in order to operate:
| • | The ignition 1 voltage |
| • | The 5-volt reference |
| • | The MAF sensor signal |
| • | The low reference |
The 5-volt reference for the MAF sensor is also supplied to additional sensors. For each of the sensors the voltage is supplied on separate ECM terminals. The terminals are connected within the ECM to the same stabilized sensor supply voltage. The 5-volt reference is shared by the following sensors:
| • | The MAF sensor |
| • | The accelerator pedal position (APP) sensor 1 |
| • | The fuel tank pressure (FTP) sensor |
| • | The air conditioning (A/C) pressure sensor |
The low reference circuit of the MAF sensor is shared with the following components:
| • | The camshaft position (CMP) sensor |
| • | The intake air temperature (IAT) sensor |
| • | The engine coolant temperature (ECT) sensor |
The ECM compares the actual MAF sensor voltage signal to the predicted MAF value. The predicted MAF value is based on engine speed and throttle valve opening. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. If the ECM detects that the actual MAF sensor signal is not within a predetermined range of the predicted MAF value, DTC P0101 sets.
Conditions for Running the DTC
| • | The ECM has counted more than 20 crankshaft revolutions. |
| • | The engine speed is more than 300 RPM. |
| • | The engine has been running for more than 0.5 seconds in order to allow the MAF sensor hot film element to heat up. |
| • | The ignition 1 signal is more than 10 volts. |
Conditions for Setting the DTC
The ECM detects that the actual MAF sensor signal is not within a predetermined range of the predicted MAF value for more than 2 seconds.
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 for the following conditions: |
| - | A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor. |
| - | Any contamination of the hot film element of the MAF sensor may cause this DTC to set. |
| - | A skewed or stuck throttle position (TP) sensor 1 or TP sensor 2 may cause this DTC to set. |
| - | A wide-open throttle acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 3-7 g/s at idle to 72 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. |
| • | If the condition is intermittent, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
This step will determine if the MAF sensor voltage is less than the proper range at idle.
-
This step will determine if the MAF sensor voltage is more than the proper range at idle.
-
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.
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-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||||
2 |
Important: If you were sent here from P0171, proceed to Step 4.
Does the scan tool display any other DTCs set? | -- | Go to Step 3 | |||||||||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||||||||||||||||||||
Is the MAF sensor voltage less than the specified range? | 1-1.6 V | Go to DTC P0102 | Go to Step 5 | |||||||||||||||||||||||
Observe the MAF sensor voltage with a scan tool. Is the MAF sensor voltage more than the specified range? | 1-1.6 V | Go to DTC P0103 | Go to Step 6 | |||||||||||||||||||||||
Is the TP sensor 1 angle within the specified range? | 98-100% | Go to Step 7 | Go to DTC P0121 | |||||||||||||||||||||||
Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 | |||||||||||||||||||||||
8 | Test for an intermittent and for a poor connection at the MAF sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | ||||||||||||||||||||||
9 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||||||||||||||
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 | ||||||||||||||||||||||
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||||||||||
