Circuit Description
The Mass Air Flow (MAF) sensor measures the amount of air that is ingested by the engine. Direct measurement of air entering the engine is more accurate than calculating the airflow from other sensor inputs. The MAF sensor has a switched battery feed, a ground, a signal circuit and a signal return circuit.
The MAF sensor used on this vehicle is a hot film type and is used to measure air flow rate. The MAF output voltage is a function of the power required to keep the air flow sensing elements at a fixed temperature above the ambient temperature. The air flowing through the sensor cools the sensing elements. The amount of cooling is proportional to the amount of air flow. As the air flow increases, a greater amount of current is required to maintain the hot film at a constant temperature. The MAF sensor converts the changes in current draw to a voltage signal read by the ECM. The ECM calculates the air flow based on this signal.
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
| • | None of the follwoing DTCs are set: P0100, P0120, P0505, P0506 or P0507. |
| • | The engine speed is greater than 520 RPM |
| • | The ECT is greater than 80°C (176°F) |
| • | The engine is running for longer than 5 seconds. |
Conditions for Setting the DTC
| • | The TPS Load signal is between 2.0 ms and 3.3 ms |
| • | The condition met for at least 7 seconds |
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. |
Diagnostic Aids
Use the Connector Test Adapter Kit J 35616 for any test that requires probing the ECM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.
Check for the following conditions:
| • | Slewed or stuck TP sensor. A malfunctioning TP sensor or TP sensor circuit can cause the ECM to incorrectly calculate the predicted mass air flow value. Observe the Throttle Angle with the throttle closed. If the Throttle Angle reading is not within the typical scan tool value(s), check for the following conditions and repair as necessary: |
| - | The TP sensor signal circuit shorted to voltage |
| - | A poor connection or a high resistance in the TP sensor ground circuit. |
| - | If none of the above conditions are noted and the Throttle Angle reading at closed throttle is not within the typical scan tool value(s), replace the TP sensor. |
| • | Poor connections at the ECM or at the component. Inspect the harness connectors for the following conditions: |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| - | Refer to Engine Control Module Diagnosis , Checking Terminal Contact, for the proper procedure. |
| • | A misrouted harness. Inspect the harness to ensure that the harness is not routed too close to any high voltage wires such as spark plug leads, or too close to any high current devices such as the alternator, the motors, the solenoids etc. |
| • | A damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any of the related connectors and the wiring harnesses. A change in the display may help to locate the fault. |
| If the sensor signal is only affected when the harness is moved at a component, and there is no problem with the harness or the connections, the component may be damaged. |
| • | A plugged intake air duct or a dirty air filter element. A Wide-Open throttle acceleration from a stop should cause the Mass Air Flow displayed on a scan tool to increase from about 4-7 gm/s at idle to 100 gm/s or greater at the time of the 1-2 shift. If not, check for a restriction. |
| • | Water entering the air intake system that reaches the MAF sensor could cause this DTC to set. The water rapidly cools the hot wires in the sensor, causing a false indication of excessive airflow. Check the air filter/housing/duct work for evidence of water intrusion. |
Refer to Symptoms , Preliminary Checks, for the intermittents.
Test Description
The number(s) below refer to the step numbers on the diagnostic table.
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Using the Freeze Frame data may aid in locating an intermittent condition. If the DTC cannot be duplicated, review the information in the Freeze Frame. Try to operate the vehicle within the same freeze frame conditions (the RPM, the MAF, the vehicle speed, the temperature etc.) that were noted. This process may help in order to recreate the malfunction.
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Any un-metered air may cause this DTC to set. Check the PCV system for vacuum leaks. Then, make sure that the engine oil dip stick and the oil fill cap are fully seated.
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The remainder of the table is the circuit check from DTC P0100. A definite open, short or short to B+ will set DTC P0100. However, a high circuit resistance causing poor grounds or a lower than normal supply voltage could slew the sensor output and cause this DTC to set.
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The scan tool display should go to the maximum value for this parameter (about 5 volts), although the actual voltage through the test light is higher.
Step | Action | Value(s) | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||||||
2 | Is DTC P0120 also set? | -- | The TP system must be diagnosed first. Go to the appropriate diagnostic procedure. | |||||||||||||||
3 | Is DTC P0100 also set? | -- | ||||||||||||||||
Do both parameters increase in value when the WOT maneuver is performed? | -- | |||||||||||||||||
Was the MAF sensor signal the signal that did not increase in value when the WOT maneuver was performed? | -- | |||||||||||||||||
Is this DTC set? | -- | Refer to Diagnostic Aids | ||||||||||||||||
7 | Check for the following conditions:
Was a problem found and corrected? | -- | ||||||||||||||||
8 |
Does the scan tool indicate the specified voltage? | 0V | ||||||||||||||||
9 | Probe the ground circuit in the MAF sensor harness connector with test light J 34142-B connected to B+. Does the test light illuminate? | -- | ||||||||||||||||
10 | Probe the signal return circuit in the MAF sensor harness connector with test light J 34142-B connected to B+. Does the test light illuminate? | -- | ||||||||||||||||
Is continuity indicated? | -- | |||||||||||||||||
12 |
Is the voltage present? | -- | ||||||||||||||||
13 |
Does the scan tool indicate the voltage shown? | 5.0V | ||||||||||||||||
14 | Probe the MAF sensor B+ supply circuit in the MAF sensor harness connector with the test light J 34142-B connected to ground. Does the test light illuminate? | -- | ||||||||||||||||
15 |
Is continuity indicated? | -- | ||||||||||||||||
16 | Check for continuity between the MAF sensor signal circuit and ground with the DVM J 39200 . Is continuity indicated? | -- | ||||||||||||||||
17 | Repair the harness/connections as necessary. Refer to Test Description. Is the action complete? | -- | -- | |||||||||||||||
18 | Repair the open/high resistance in the ground circuit. Is the repair completed? | -- | -- | |||||||||||||||
19 | Repair the open/high resistance in the signal return circuit. Is the repair completed? | -- | -- | |||||||||||||||
20 | Repair the signal circuit that is shorted to voltage. Is the repair completed? | -- | -- | |||||||||||||||
21 | Repair the open/high resistance in the switched B+ circuit. Is the repair completed? | -- | -- | |||||||||||||||
22 | Repair the open/high resistance in the signal circuit. Is the repair completed? | -- | -- | |||||||||||||||
23 | Repair the signal circuit shorted to ground. Is the repair completed? | -- | -- | |||||||||||||||
24 | Check for a poor connection or poor terminal tension at the MAF sensor harness connector. Refer to Electrical Diagnosis in Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Was a problem found and corrected? | -- | ||||||||||||||||
25 | Replace the MAF sensor. Is the repair completed? | -- | -- | |||||||||||||||
26 | Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Electrical Diagnosis in Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Was a problem found and corrected? | -- | ||||||||||||||||
27 |
Important: This vehicle is equipped with a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming . Is the action complete? | -- | -- | |||||||||||||||
28 |
Is this DTC set? | -- | ||||||||||||||||
29 | Were there any additional DTCs noted during the Powertrain OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | The System is OK |
