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 83 (ENGINE CONTROLS - SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0446: EVAP VENT SOLENOID VALVE CONTROL SYSTEMDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Procedures
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 Saturn LW200, 2002 Saturn L200, and 2002 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.
- Turn ignition ON, engine OFF. Using scan tool, monitor EVAP VENT CKT OPEN SHORT TO GND. If feedback reads YES, go to next step. If feedback reads NO, go to step 5 .
- Check BCM/ECM/CRUISE/ABS fuse (10 amp). Replace and retest if open. If fuse continues to open, check for short to ground in Pink wire or Orange wire between under hood fuseblock and EVAP vent solenoid. Raise vehicle. Remove right rear inner fender well. Disconnect EVAP vent solenoid. Connect Noid Light (SA9194E) between terminals at EVAP vent solenoid connector. Using scan tool, monitor EVAP VENT CKT OPEN SHORT TO GND. If feedback reads YES, go to next step. If feedback reads NO, check EVAP solenoid connector. If connector is okay, replace EVAP vent solenoid.
- Connect a test light between ground and EVAP vent solenoid connector terminal "A" (Orange wire). If test light is on, go to next step. If test light is off, repair open in Orange wire or Pink wire between under hood fuseblock and EVAP vent solenoid.
- Turn ignition off. Disconnect PCM connector J1. Check for continuity between EVAP vent solenoid connector terminal "B" (White wire) and ground. If continuity exists, repair short to ground in White wire between EVAP vent solenoid and PCM. If continuity does not exist, check White wire between EVAP vent solenoid and PCM for open. If wire is okay, replace PCM.
- Turn ignition ON, engine OFF. Using scan tool, command EVAP VENT SOLENOID on, while monitoring EVAP VENT CKT SHORT TO VOLTS. If feedback reads YES, go to next step. If feedback reads NO, problem is intermittent. See DIAGNOSTIC AIDS .
- Raise vehicle. Remove right rear wheel well. Disconnect EVAP vent solenoid. Connect Noid Light (SA9194E) across EVAP vent solenoid connector terminals. Using scan tool, command EVAP VENT SOLENOID on, while monitoring EVAP VENT CKT SHORT TO VOLTS. If feedback reads YES, check White wire between EVAP vent solenoid and PCM for short to voltage. If wire is okay, replace PCM. If feedback reads NO, replace EVAP vent solenoid.
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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.