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 MANUALSCHEVROLET2001CHEVY EXPRESS G2500, VAN CARGO EXTENDED, 5.7 R, L31/KL8REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 4 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.3L)DIAGNOSTIC TESTSDTC P1639: 5-VOLT REFERENCE 2 CIRCUITDESCRIPTION
2001 Chevrolet Chevy Express G2500, Van Cargo Extended, 5.7 R, L31/KL8
DTC P1639: 5-Volt Reference 2 Circuit: Description
2001 Chevrolet Chevy Express G2500, Van Cargo Extended, 5.7 R, L31/KL8SECTION Description
WARNING: This page is about a different variant/trim than selected.
Powertrain Control Module (PCM) uses 5-volt reference 2 circuit as a sensor feed for Fuel Tank Pressure (FTP) sensor. PCM monitors voltage on 5-volt reference 2 circuit. DTC P1639 sets if voltage is out of tolerance.
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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.