Evaporative Emission System (EVAP) Malfunction
Code P0440 indicates a general functional failure in the EVAP system. During closed-loop testing, the fuel tank failed to hold negative vacuum. The most frequent causes are a loose or deteriorated fuel filler gas cap, stuck purge valve, or rusted filler neck.
Inspect your gas cap rubber seal for cracks, dry rot, or grime. Wipe the fuel neck mating rim clean and tighten the cap until it clicks 3 times. If code returns, test the under-hood purge solenoid for vacuum leakage.
Interactive Symptom Pinpoint Troubleshooter
Answer 2 diagnostic tests to isolate the exact component failure for P0440.
Does the EVAP purge solenoid hold complete vacuum when unpowered on the workbench?
Live Scanner & Multimeter Benchmark Values
Compare your live OBD-II PID sensor data against OEM factory operating specs for P0440.
| Monitored Parameter / Sensor PID | Healthy OEM Operating Range | Fault Threshold (Triggers P0440) |
|---|---|---|
| Fuel Tank Pressure (FTP) Sensor (Cap Off) | 1.4V – 1.6V (Atmospheric 0 in. H2O) | >2.5V or <0.5V indicates dead FTP sensor |
| EVAP Purge Solenoid (Unpowered, Key Off) | 100% Airtight seal | Passes air/vacuum freely (stuck open solenoid) |
Symptoms Associated with P0440
Drivers typically observe the following symptoms when the ECM flags P0440:
Common Root Causes & Statistical Probability Matrix
Statistical breakdown of what triggers this code based on automotive repair shop data.
Step-by-Step Diagnostic & Repair Procedure
Follow this logical order to isolate and repair P0440 before spending money on costly parts.
Step 1: Inspect Gas Cap
Check rubber gasket for cracking or deformation. Clean filler neck.
Step 2: Purge Solenoid Bench Test
Remove purge valve under hood. Blow through it; if air passes freely, it is stuck open.
Step 3: Smoke Test EVAP Lines
Inject mineral oil smoke into test port to reveal leaking lines.
Vehicle-Specific Failure Trends & Technical Bulletins
Real workshop failure patterns reported by mechanics across popular makes and models for P0440.
Toyota Corolla / Camry / RAV4
Chevy Silverado / Tahoe
Dave Miller, ASE Master Tech
ASE L1 Certified Master ReviewerASE Certified Master Automobile Technician (A1-A8) & L1 Advanced Engine Performance • 24 years automotive diagnostic experience
“Always verify sensor voltages and harness grounds before purchasing replacement electronic components.”