EVAP System Small Leak Detected
What Does P0442 Mean?
P0442 means the EVAP (evaporative emission control) system has detected a small leak — typically between 0.020 and 0.040 inches in diameter. The system tests itself by sealing the fuel tank, applying vacuum, and watching for pressure to hold. If it bleeds off too fast, P0442 sets.
On the 2007–2019 Chevy Silverado, a loose or worn gas cap is the cause in over half of P0442 cases. The next most common culprits are cracked EVAP hoses and a failed purge or vent solenoid. None will leave you stranded.
Symptoms
Common Causes
- 1.Loose or worn gas cap55%
Most common cause. Cap seal hardens with age and stops sealing at 5+ years.
- 2.Cracked EVAP hose20%
Rubber lines from tank to canister get brittle. Check near the fuel filler neck.
- 3.Failed purge valve solenoid12%
Stuck-open purge valve leaks vacuum constantly.
- 4.Failed vent solenoid8%
Mounted near the charcoal canister, often dirty from road debris.
- 5.Cracked EVAP canister3%
Common on lifted/off-road trucks that hit obstacles.
- 6.Bad fuel tank o-ring or pump seal2%
Last resort — drop the tank only after everything else checks out.
Step-by-Step Diagnosis
Tighten or replace the gas cap
Remove the gas cap, inspect the o-ring for cracks/hardening. Reinstall and click it 3 times. Clear the code, drive 2–3 days. If P0442 returns, replace the cap with an AC Delco unit (~$15).
Visual inspect EVAP lines
Trace the EVAP lines from the fuel tank to the engine bay. Look for cracks, kinks, rodent damage, and loose clamps. Common failure: hose from charcoal canister to vent solenoid.
INSPECTION CHECKLIST:
[ ] Gas cap seal intact
[ ] Filler neck hose clamped
[ ] Charcoal canister hoses intact
[ ] Purge valve hose to intake
[ ] Vent solenoid filter cleanSmoke test the EVAP system
A smoke machine pumps low-pressure smoke through the system; leaks show as wispy escape points. This is the gold-standard test and catches leaks too small to find by eye. Shop cost: $60–$120, often free if you buy parts there.
Test the purge and vent solenoids
With a bidirectional scanner, command each solenoid open and closed. Listen for a click and watch fuel tank pressure react. No click = bad solenoid or wiring.
Clear and drive cycle
The EVAP monitor requires a specific drive cycle to re-run: cold start, drive 15+ minutes, fuel between 1/4 and 3/4 full, OAT 40–95°F. Don't expect immediate verification.
How to Fix It
Parts needed:
- AC Delco Gas Cap (GT337) — approx $15
- ACDelco Purge Solenoid — approx $38
- ACDelco Vent Solenoid — approx $45
- Dorman EVAP Hose Kit — approx $28
- Charcoal Canister (OE) — approx $165
Procedure:
- Tighten/replace gas cap — wait 3 days.
- If returns: pull codes again to confirm P0442 only.
- Visually inspect all EVAP hoses for cracks.
- If no visible damage, take to a shop for a smoke test (~$80).
- Replace whichever component the smoke escapes from.
- Clear code and complete an EVAP drive cycle.
Will It Pass Emissions?
Repair Cost Breakdown
| Part / Region | DIY Cost | Shop Labor | Total Range |
|---|---|---|---|
| Most regions (DIY) | $40 | — | $15–$95 |
| Most regions (shop) | — | $240 | $160–$520 |
Estimates based on aggregated independent shop quotes; dealer labor adds 30–50%. Excludes diagnostic fee ($80–$150).
FAQs
Sources & References
- §SAE J2012 — Diagnostic Trouble Code Definitions — Standardized OBD-II code definitions used by all manufacturers.
- §EPA OBD Regulations (40 CFR §86.1806-05) — Federal on-board diagnostic requirements for light-duty vehicles.
Cost figures are aggregated from real customer invoices at our shop plus quotes from RepairPal and Mitchell1 labor guides. Diagnostic procedures verified against factory service information (ALLDATA / Mitchell1).
// About the author
Mike Reeves — Independent shop owner in Phoenix, AZ. Specializes in driveability diagnostics on domestic and Asian gas engines. Writes our powertrain coverage. More about our team →