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 324 (CHARGING SYSTEM)DIAGNOSTIC TESTSDTC P0622: IMPROPER PULSE WIDTH MODULATED SIGNALCONDITIONS FOR SETTING DTC
1999 GMC Forward Control 5.7 R, Automatic
Conditions For Setting DTC
1999 GMC Forward Control 5.7 R, AutomaticSECTION Conditions For Setting DTC
WARNING: This page is about a different car, the 2003 Oldsmobile Aurora and 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
- During the key ON test, the PCM detects a PWM signal greater than 65 percent for at least 5 seconds.
- Or, during the RUN test, the PCM detects a PWM signal less than 5 percent for at least 15 seconds.
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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.