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
The DTC P0440 Evaporative Emission (EVAP) System diagnostic evaluates the operation of EVAP control system. Powertrain Control Module (PCM) will command EVAP vent valve ON, CLOSED, and purge solenoid and EVAP pressure switching solenoid ON, OPEN, with engine running. This allows engine vacuum into EVAP system. PCM then commands purge solenoid OFF, CLOSED, sealing the system. PCM then monitors fuel tank vapor pressure sensor signal to determine if there is vacuum decay. A rise or rapid increase in pressure indicates there is a large leak in the evaporative emission system. If PCM detects the vacuum level was not achieved and vacuum decay was evident a DTC P0440 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.