Symptom Diagnosis

1999 GMC Forward Control 5.7 R, AutomaticSECTION Symptom Diagnosis

Symptom checks should not be used unless symptom occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in appropriate BASIC DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS articles were performed before diagnosing a symptom. Symptoms available for diagnosis include:

  • Hard Start
  • Stalls After Starting
  • Hesitation, Sag Or Stumble
  • Vehicle Surges Or Chuggles
  • Lack Of Power Or Sluggish
  • Engine Backfires
  • Cuts Out, Misses
  • Rough, Unstable Or Incorrect Idle
  • Engine Will Not Idle
  • Poor Fuel Economy
  • Engine Dieseling/Run-On
  • Detonation/Spark Knock
  • Excessive Exhaust Emissions Or Odors

RENDER: 1.0x

NO RELATED

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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.