GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC MD Steel Tilt (W Model) 🢒 DTC 🢒 DTC P0101

Circuit Description

The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The powertrain control module (PCM) uses the MAF sensor frequency signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load situation. The MAF sensor has an ignition 1  voltage circuit, a ground circuit and a signal circuit. The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The PCM uses the barometric pressure (BARO) at key ON, and the engine RPM in order to calculate a predicted MAF value. The PCM compares the actual MAF sensor frequency signal to the predicted MAF value in order to determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. DTC  P0101 will set if the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value.

Conditions for Running the DTC
    • DTCs P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0121, P0122, P0123, P0335, P0336, P0401, P0440, P0442, P0443, P0446, P0449, P1106, P1107, P1111, P1112, P1121, P1122, P1441 are not set.
    • The engine is running.
    • The ignition 1  signal is between 11-18 volts.
    • The throttle position (TP) sensor angle is steady within a range of 5 percent or less.
    • The TP sensor angle is less than 95 percent.
    • The MAP sensor is less than 80 kPa.
    • All of the above conditions are present for at least 2 seconds.

Conditions for Setting the DTC
    • The actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value.
    • The above condition is present for 8 seconds.

Action Taken When the DTC Sets
    • The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic has been run and failed.
    • The PCM will store the conditions which were present when the DTC set as Freeze Frame/Failure Records data.

Conditions for Clearing the MIL/DTC
    • The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
    • The history DTC will clear after 40  consecutive warm-up cycles have occurred without a malfunction.
    • Use the scan tool in order to clear the DTCs.

Diagnostic Aids

Inspect for the following conditions:

    • A misrouted harness--Inspect the harness of the MAF sensor in order 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
    • Any unmetered air that enters the engine may cause this DTC to set. Verify that the oil dipstick is fully seated and the oil filler cap is secure.
    • Inspect for any vacuum leaks downstream of the MAF sensor.
    • A wide open throttle acceleration should cause the MAF display to increase from 4-7 g/s at idle to 150 g/s or more during the 1-2 shift. If the change in the display is not observed, inspect for a restriction.
    • The barometric pressure that is used in order to calculate the predicted mass air flow value is based on the manifold absolute pressure (MAP) sensor at key ON. A skewed MAP sensor will cause the calculated mass air flow value to be inaccurate. The value shown for the MAP sensor display will vary with the altitude. With the ignition ON and the engine OFF, 103  kPa is the approximate value at or near sea level. The value decreases by approximately 3 kPa for every 305 m (1,000 feet) of altitude.

If you suspect the vehicle condition may be related to aftermarket accessories, refer to Checking Aftermarket Accessories in Wiring Systems.

If the condition is intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Any unmetered air that enters the engine may cause this DTC to set. This step eliminates the conditions which can cause a DTC to set with a normally operating MAF sensor.

    2.

  2. This step verifies the signal circuit from the MAF sensor electrical connector to the PCM. A voltage reading of less than 4 volts or greater than 6 volts indicates a malfunction in the wiring or a poor connection.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls ?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Install a scan tool.
  2. Start the engine.
  3. Monitor the Diagnostic Trouble Code (DTC) Information using the scan tool.

Does the scan tool display any other DTCs set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3
  1. Observe and record the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30  seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Let the engine idle at the normal operating temperature.
  2. With a scan tool, observe the MAP sensor voltage parameter.

Does the scan tool indicate that the MAP sensor voltage is within the specified range?

0.8-4 V

Go to Step 5

Go to DTC P0106

5

  1. Turn OFF the ignition.
  2. Inspect for the following conditions:
    3. • Objects blocking the air inlet screen of the MAF sensor
    • A plugged or collapsed air intake duct
    • A dirty air filter element
  3. Inspect for vacuum leaks in the following components:
    4. • The intake manifold
    • The throttle body
    • The exhaust gas recirculation (EGR) valve flange and pipe
    • The MAF sensor seal
    • The MAP sensor seal
    • The evaporative emission (EVAP) canister purge valve seal
    • The fuel meter body seal
    • The crankcase ventilation system
    • The brake booster system
    • The air induction system

Did you find and correct the condition?

--

Go to Step 23

Go to Step 6

6
  1. Turn OFF the ignition.
  2. Remove the MAP sensor from the engine vacuum source. Refer to Manifold Absolute Pressure Sensor Replacement .
  3. Leave the electrical harness connected.
  4. Connect a hand operated vacuum pump to the MAP sensor.
  5. Turn ON the ignition, with the engine OFF.
  6. With a scan tool observe or record the MAP sensor kPa parameter display as you SLOWLY apply vacuum 1 inch Hg at a time up to 20 inches Hg as indicated on the pump gauge. Each 1  inch of vacuum applied should result in a 3 kPa to 4  kPa drop in the MAP sensor value on the scan tool. The value should change smoothly with each 1  inch increase in vacuum.

Does the scan tool indicate that the MAP sensor value changed smoothly through the entire range of the test?

--

Go to Step 7

Go to DTC P0106

7

Apply 20  inches Hg vacuum to the MAP sensor.

Does the scan tool indicate that the MAP sensor value is equal to or less than the specified value?

34  kPa

Go to Step 8

Go to DTC P0106

8

Disconnect the vacuum source from the MAP sensor.

Does the scan tool indicate that the MAP sensor value returned to the original value that was observed in step 6?

--

Go to Step  9

Go to DTC P0106

9

Use a scan tool in order to observe the TP sensor angle parameter from closed throttle to wide open throttle (WOT).

Does the scan tool indicate that the TP sensor value changed smoothly and completely through the specified range of the test?

0-100%

Go to Step  10

Go to DTC P0121

10

  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the MAF sensor. Refer to Mass Airflow Sensor Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the signal circuit of the MAF sensor to a good ground. Refer to Circuit Testing in Wiring Systems.

Does the voltage measure near the specified value?

5 V

Go to Step  11

Go to Step  12

11

Connect a test lamp between the ignition 1  voltage circuit of the MAF sensor and the ground circuit of the MAF sensor. Refer to Circuit Testing in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step  19

Go to Step  14

12

Does the voltage measure less than the specified value?

4.5 V

Go to Step  15

Go to Step  13

13

Important:: Disconnecting the PCM connectors may eliminate the short to voltage if the signal circuit is shorted to another PCM circuit.

  1. Turn OFF the ignition.
  2. Disconnect the PCM. Refer to Powertrain Control Module Replacement .
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the signal circuit of the MAF sensor to a good ground.

Does the voltage measure at the specified value?

0 V

Go to Step  22

Go to Step  18

14

Connect a test lamp between the ignition 1  voltage circuit of the MAF sensor and a good ground. Refer to Circuit Testing in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step  16

Go to Step  17

15
  1. Turn OFF the ignition.
  2. Disconnect the PCM. Refer to Powertrain Control Module Replacement .
  3. Test the signal circuit between the PCM and the MAF sensor for the following conditions:
    • A high resistance or an open
    • A short to ground
    • A short to the ground circuit of the MAF sensor--Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 20

16

Repair the high resistance or an open in the ground circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step  23

--

17

Important: The ignition  1 voltage circuit of the MAF sensor is spliced to other components on the vehicle.

  1. Repair the short to ground or an open in the ignition 1 voltage circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems.
  2. Replace the fuse if necessary.

Did you complete the repair?

--

Go to Step  23

Go to Step  21

18

Repair the short to voltage in the signal circuit of the MAF sensor. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step  23

--

19

Inspect for poor connections at the harness connector of 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  23

Go to Step  21

20

Inspect for poor connections at the harness connector of the PCM. 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  23

Go to Step 22

21

Replace the MAF sensor. Refer to Mass Airflow Sensor Replacement .

Did you complete the replacement?

--

Go to Step  23

--

22

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step  23

--

23
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 24

Go to Step 2

24

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK