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 150 (ENGINE CONTROL SYSTEM - TROUBLE SHOOTING - NO CODES)INTERMITTENTSINTERMITTENT CONDITIONSINTERMITTENT MALFUNCTION INDICATOR LIGHT
1999 GMC Forward Control 5.7 R, Automatic
Intermittent Malfunction Indicator Light
1999 GMC Forward Control 5.7 R, AutomaticSECTION Intermittent Malfunction Indicator Light
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
The following conditions may cause intermittent MIL operation with no DTCs stored:
- A defective relay, control module driven solenoid, or a switch that causes electrical system interference. Usually the symptom will occur when the faulty component is operating.
- Any Ignition Control (IC) wires routed near the generator or near secondary ignition system wires and components.
- An ignition system secondary voltage that is arcing and shorting to ground.
- Any poor ignition control circuit or ignition module grounds.
- A MIL control circuit that is intermittently shorting to ground.
- Any faulty diodes in the generator or charging system circuits.
- Improper installation of add-on electrical devices. These can include alarm systems, 2-way radios, lighting systems, electrical motors.
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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.