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.
SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 86 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 3.0L)DIAGNOSTIC TESTSDTC P0446: EVAP VENT SYSTEM PERFORMANCEDIAGNOSTIC 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 Vue. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTC P0440, P0442, P0446 or P0496 is set, EVAP special functions on scan tool will not be allowed. Clear DTCs before performing these tests.
- Turn ignition on, engine off. Remove fuel cap. Using scan tool, monitor fuel tank pressure sensor. If voltage is 1.4-1.6 volts, go to next step. If voltage is less than 0.1 volt, see DTC P0452: EVAP FUEL TANK PRESSURE SENSOR CIRCUIT - LOW VOLTAGE . If voltage is 0.10-1.40 volts or 1.60-4.75 volts, replace FTP sensor. If voltage is more than 4.75 volts, see DTC P0453: EVAP FUEL TANK PRESSURE SENSOR CIRCUIT - HIGH VOLTAGE .
- Install fuel cap. Clear ECM DTCs. Start engine and let idle. Using scan tool, perform EVAP PURGE/SEAL special function by commanding a 10 percent duty cycle to the EVAP purge solenoid. Wait for fuel tank pressure to reach 2.44 volts or more, then using scan tool, command EVAP purge solenoid off by pressing EXIT. If fuel tank pressure returns to 1.4-1.6 volts within 5 seconds, problem is intermittent. See DIAGNOSTIC AIDS . If fuel tank pressure does not return to 1.4-1.6 volts within 5 seconds, go to next step.
- Turn ignition on, engine off. Raise vehicle to chest height. Using scan tool, command EVAP VENT SOLENOID on and off while listening for the solenoid clicking at EVAP canister underneath vehicle directly in front of fuel tank. If the solenoid clicks, EVAP vent system is blocked. Check the following:
- EVAP vent foam filter plugged (can be removed by taking EVAP canister cover off behind EVAP solenoid).
- Blocked EVAP canister or kinked/pinched EVAP lines/hoses between fuel filler neck and EVAP vent solenoid. If solenoid does not click, replace EVAP vent solenoid.
RENDER: 1.0x
NO RELATED
Recommended Tools & Savings
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.