Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 89 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.0L)DIAGNOSTIC TESTSDTC P0300-P0308: 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 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
- DTCs P0101, P0102, P0103, P0106, P0107, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0218, P0335, P0336, P0340, P0341, P0385, P0386, P0502, P0503, P0705, P0713, P1114, P1115, P1121, P1122, P1336, or P1372 are not set.
- Engine speed is 500-5850 RPM.
- System voltage is 9-18 volts.
- The ECT indicates an engine temperature between 19-248°F (-7-120°C). If the start-up ECT is below 19°F (-7°C), then the test is delayed until ECT is more than 70°F (21°C).
- Throttle angle is steady.
- The A/C compressor clutch state is steady.
- The Exhaust Gas Recirculation (EGR) flow test is inactive.
- Fuel level is more than 10 percent.
- Decel fuel cutoff mode and torque management are not active.
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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.