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 93 (ENGINE CONTROL SYSTEM TROUBLESHOOTING - NO CODES)INTERMITTENTSELECTROMAGNETIC INTERFERENCE (EMI) & ELECTRICAL NOISE
1999 GMC Forward Control 5.7 R, Automatic
Electromagnetic Interference (EMI) & Electrical Noise
1999 GMC Forward Control 5.7 R, AutomaticSECTION Electromagnetic Interference (EMI) & Electrical Noise
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2002 Saturn SL2, 2002 Saturn SL1, 2002 Saturn SL, 2002 Saturn SC2, and 2002 Saturn SC1. However, it is still accessible from the selected car via links, so may be relevant.
Some electrical components or circuits are sensitive to Electromagnetic Interference (EMI) or other types of electrical noise. Perform the following procedures:
- Inspect for a misrouted harness that is too close to a high voltage or high current device. This condition may induce electrical noise on a circuit that could interfere with normal circuit operation. Inspect for wires that are too close to the following devices:
- Secondary ignition components.
- Motors.
- The generator.
- Determine whether the electrical system interference is caused by a malfunctioning relay, PCM driven solenoid or switch. These components may cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
- Determine whether non-factory or aftermarket add-on accessories are installed in the vehicle. These accessories may lead to an emission related OBD-II failure. Determine if any of the following non-factory or aftermarket add-on accessories is causing the intermittent:
- Lights.
- 2-way radios.
- Amplifiers.
- Electric motors.
- Remote starters.
- Alarm systems.
- Cell phones.
- Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode.
- Test for proper performance of the generator. See ON-VEHICLE TESTING in appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS.
- If a DTC is determined to be intermittent, and the tests in this section do not reveal a problem, see VEHICLE DATA RECORDER .
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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.