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 26 (THEFT DETERRENT SYSTEM)DIAGNOSTIC TESTSDTC P1631: INVALID PASSWORD RECEIVEDCONDITIONS FOR CLEARING MIL/DTC
1999 GMC Forward Control 5.7 R, Automatic
Conditions For Clearing MIL/DTC
1999 GMC Forward Control 5.7 R, AutomaticSECTION Conditions For Clearing MIL/DTC
WARNING: This page is about a different car, the 2002 GMC Savana, 2002 Chevrolet Chevy Express, 2001 GMC Savana, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
- A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.
- A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.
- Use the scan tool Clear Information function.
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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.