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.
Circuit Description
When running the DTC P0446 Evaporative Emission (EVAP) Vent System Performance diagnostic, Powertrain Control Module (PCM), monitors Fuel Tank Pressure (FTP) sensor. When vapor pressure rises to a specified value, PCM commands the vent valve open, and monitors FTP sensor signal. Pressure will increase rapidly because of the air allowed into the system. No increase or an increase below a specified rate indicates a restriction on the air inlet side. PCM then commands the pressure switching solenoid closed. This blocks air from entering the tank side of the system. PCM monitors FTP sensor and looks for a decrease in pressure rise. If there is no change in pressure PCM concludes pressure switching solenoid did not close. If PCM does not detect an increase in pressure, or rise in pressure does not change, a DTC P0446 will set.
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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.