GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC P2004

Circuit Description

The mass air flow (MAF) sensor is an air flow meter that measures the amount of air that enters the engine. It is between the air cleaner and turbocharger. A small quantity of air that enters the engine indicates deceleration or idle. A large quantity of air that enters the engine indicates acceleration or a high load condition. The MAF sensor has the following circuits:

    • An ignition voltage circuit
    • A low reference circuit
    • A MAF sensor signal circuit

The engine control module (ECM) monitors the MAF sensor signals for voltage outside the normal range of the MAF sensor. If the ECM detects an excessively low MAF sensor signal voltage, this DTC will set.

Conditions for Running the DTC
    • The ignition switch is ON.
    • The battery voltage is between 10-16 volts.

Conditions for Setting the DTC

The ECM detects that the MAF signal voltage is more than 0.08 volt.

Action Taken When the DTC Sets
    • The ECM illuminates the malfunction indicator lamp (MIL) and reduced engine power indicator lamp, if fitted, when the diagnostic runs and fails.
    • The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
    • The ECM limits fuel injection quantity for fail-safe operation.
    • The ECM closes the exhaust gas recirculation (EGR) valve and stops EGR control.
    • The ECM inhibits the cruise control.

Condition for Clearing the DTC
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • If an intermittent condition is suspected, the following may cause an intermittent:
       - Poor connections
       - A misrouted harness
       - Rubbed through wire insulation
       - Broken wire inside the insulation
    • Inspect for the following conditions:
       - Poor connection at ECM--Inspect the harness connectors for the following conditions:
   • Backed-out terminals
   • Improper mating
   • Broken locks
   • Improperly formed or damaged terminals
   • Poor terminal to wire connection
       - Damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the Mass Air Flow display on the scan tool while moving the connectors and the wiring harness related to the sensor. A change in the display will indicate the location of the fault.

Test Description

The number below refers to the step number on the diagnostic table.

  1. Operate the vehicle within the same conditions as when the DTC failed. If you can not duplicate the DTC, using the information included in the Failure Records can help to locate an intermittent condition.

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

Turn OFF the ignition for 30 seconds.

Is DTC P2004 current?

--

Go to Step 4

Go to Step 3

3

  1. Observe the Failure Records 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. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn OFF the ignition.
  2. Disconnect the mass air flow (MAF) sensor connector.
  3. Connect a DMM between the ignition voltage feed circuit and low reference circuit of the MAF sensor.
  4. Turn ON the ignition, with the engine OFF.

Is the DMM voltage less than the specified value?

Battery Voltage

Go to Step 5

Go to Step 6

5
  1. Turn OFF the ignition.
  2. Disconnect the MAF sensor connector.
  3. Connect a DMM between the low reference circuit and the signal circuit of the MAF sensor.
  4. Turn ON the ignition, with the engine OFF.

Is the DMM voltage less than the specified value?

1 V

Go to Step 8

Go to Step 7

6
  1. Test the ignition voltage feed circuit between the engine control module (ECM) main relay and the MAF sensor for the following conditions:
    2. • A short to ground circuit
    • A short to low reference circuit
    • High resistance
    • An open circuit
  2. Repair the circuits, as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

7
  1. Test the signal circuit between the ECM and the MAF sensor for the following conditions:
    2. • A short to ground circuit
    • A short to low reference circuit
    • An open circuit
    • High resistance
  2. Repair the circuits, as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the MAF sensor connector.
  3. Inspect for an intermittent or for a poor connection at the harness connector of the MAF sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
  4. Repair the connections as necessary.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

9
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Inspect for an intermittent or for a poor connection at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
  4. Repair the connections as necessary.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

Replace the MAF sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

Go to Step 9

11

Important: The new ECM must be programmed.

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data .

Did you complete the replacement?

--

Go to Step 12

--

12
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 13

13

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK