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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 58 (ENGINE CONTROLS SELF-DIAGNOSTICS - 4.3L)DIAGNOSTIC TESTSDTC P0300-P0306: ENGINE MISFIRE DETECTEDCONDITIONS FOR RUNNING DTC
1999 GMC Forward Control 5.7 R, Automatic

Conditions For Running DTC

1999 GMC Forward Control 5.7 R, AutomaticSECTION Conditions For Running DTC
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.
NOTE: If start-up ECT is less than 20°F (7°C), misfire detection is delayed until Engine Coolant Temperature (ECT) is more than 70°F (21°C). If start-up ECT is more than 20°F (7°C), misfire detection begins after a 5 second delay.
  • DTCs P0101, P0102, P0103, P0116, P0117, P0118, P0128, P0335, P0336, P0341, P0343, P0500, P0502, P0503, P1114, P1115, P1121, P1122, P1220, P1258, P1336, or P1345 are not set.
  • The fuel level is more than 10 percent.
  • Then engine speed is between 450-5000 RPM.
  • The system voltage is between 11-16 volts.
  • The Throttle Position (TP) is steady within 2 percent for 100 ms.
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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.