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 58 (ENGINE CONTROLS SELF-DIAGNOSTICS - 4.3L)DIAGNOSTIC TESTSDTC P1635: 5-VOLT REFERENCE 1 CIRCUITDESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic
DTC P1635: 5-Volt Reference 1 Circuit: Description
1999 GMC Forward Control 5.7 R, AutomaticSECTION Description
WARNING: This page is about a different car, the 2002 GMC Savana and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) uses the 5-volt reference 1 circuit as a sensor feed to the following sensors:
- The Throttle Position (TP) sensor.
- The Manifold Absolute Pressure (MAP) sensor.
- The Exhaust Gas Recirculation (EGR) valve pintle position sensor.
RENDER: 1.0x
NO RELATED
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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.