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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 58 (ENGINE CONTROLS SELF-DIAGNOSTICS - 4.3L)DIAGNOSTIC TESTSDTC P0101: MASS AIR FLOW SENSOR PERFORMANCEDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 GMC Savana and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Start the engine. Monitor the Diagnostic Trouble Code (DTC) Information with the scan tool. Does the scan tool display any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Observe the Freeze Frame/Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  4. Allow the engine to reach operating temperature. Observe the MAP sensor voltage with a scan tool. Is the MAP sensor voltage 0.8-4.0 V? If yes, go to next step. If no, see DTC P0106: MAP SYSTEM PERFORMANCE .
  5. Idle the engine. Observe the MAP sensor kPa with a scan tool. Increase the engine speed slowly to 3000 RPM and then back to idle. Does the MAP sensor kPa change smoothly and gradually through the specified range of the test? If yes, go to next step. If no, see DTC P0106: MAP SYSTEM PERFORMANCE .
    6. NOTE: If the vehicle is equipped with throttle actuator control (TAC), proceed to the next step.
  6. Turn OFF the ignition. Turn ON the ignition, with the engine OFF. Observe the TP sensor angle from closed throttle to wide open throttle. Depress completely and then release the accelerator pedal. Does the scan tool indicate that the TP sensor angle changed smoothly and completely through 0-100%? If yes, go to next step. If no, see DTC P0121: TP SENSOR PERFORMANCE .
  7. Inspect for the following conditions:
    • A restricted air intake duct.
    • A collapsed air intake duct.
    • A misaligned air intake duct.
    • A dirty air filter element.
    • A deteriorating air filter element.
    • Any objects blocking the air inlet screen of the MAF sensor.
    • Any debris on the sensing elements of the MAF sensor.
    • Any vacuum leak downstream of the MAF sensor.
    • A poor vacuum connection at the MAP sensor.
    • A restricted exhaust system.

    Did you find and correct the condition? If yes, go to step  10. If no, go to next step.

  8. Test for an intermittent and for a poor connection at the MAF sensor. Did you find and correct the condition? If yes, go to step  10. If no, go to next step.
  9. Replace the MAF sensor. After repairs, go to next step.
  10. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  11. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.