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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 89 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.0L)DIAGNOSTIC TESTSDTC P0101: MASS AIRFLOW SENSOR SYSTEM 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 Oldsmobile Aurora. 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, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: If DTC P0101 and P0121 are both set, go to step  4.
  2. Start engine. Using scan tool, check for any other DTCs that are set. Does scan tool display any other DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  3. Using scan tool, observe and record FREEZE FRAME/FAILURE RECORDS data for this DTC. Turn ignition off for 30 seconds. Start engine. Operate vehicle within Conditions For Running DTC or as close to recorded FREEZE FRAME/FAILURE RECORDS data as possible. If DTC resets, go to next step. If DTC does not reset, see DIAGNOSTIC AIDS .
  4. Allow engine to reach operating temperature. Observe MAP sensor voltage with a scan tool. Is MAP sensor voltage is within 0.8-4.0 volts? If yes, go to next step. If no, see DTC P0106: MAP SYSTEM PERFORMANCE .
  5. Operate engine at idle. Using scan tool, observe MAP sensor kPa. Increase 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. Turn ignition off. Turn ignition on, with engine off. Observe TP sensor angle from closed throttle to Wide Open Throttle (WOT). Completely depress and then release accelerator pedal. Does scan tool indicate that TP sensor angle changed smoothly and completely through the specified range of the test (0-100 percent)? If yes, go to next step. If no, go to DTC P0121: THROTTLE POSITION SENSOR CIRCUIT INSUFFICIENT ACTIVITY .
  7. Check for a restricted air intake duct, collapsed air intake duct, misaligned air intake duct, dirty air filter element, deteriorating air filter element, any objects blocking MAF sensor air inlet screen, debris on sensing elements of MAF sensor, any vacuum leak downstream of MAF sensor, poor vacuum connection at MAP sensor, or 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 MAF sensor. Did you find and correct the condition? If yes, go to step  10. If no, go to next step.
  9. Replace MAF sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to next step.
  10. Use the scan tool in order to clear the DTCs. 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. With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
RENDER: 1.0x

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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.