Diagnostic Aids

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Aids
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Inspect for the following conditions:

  • A misrouted harness Inspect the harness of the MAF sensor in order to verify that the harness is not routed too close to the following components:
    1. The secondary ignition wires or coils.
    2. Any solenoids.
    3. Any relays.
    4. Any motors.
  • A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor.
  • A Wide Open Throttle (WOT) acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 4-7 g/s at idle to 150 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
  • A resistance of 20 ohms or more on the ground circuit of the MAF sensor can cause this DTC to set.

If the problem is intermittent, See INTERMITTENT CONDITIONSΒ  under SELF-DIAGNOSTIC SYSTEM.

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When to See a Mechanic

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

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