P0442 — Evaporative Emission System Leak Detected (Small Leak)
P0442 sets for a small EVAP leak (typically 0.040 inch range), between the large and very-small leak thresholds. Ordered gas-cap → smoke → valve seal testing finds the leak efficiently. Purge valves that do not seal properly are a frequent cause. After repair, ensure the EVAP monitor runs to completion.
Fault Overview
Gas cap, cracked EVAP lines, purge or vent valve, canister, and filler-neck issues are the primary causes. Treat P0442 like a medium-difficulty EVAP leak — still start with the gas cap.
Engine & Platform Coverage
Symptoms
- •P0442
- •small EVAP leak
- •EVAP leak detected
- •P0442 gas cap
- •P0442 purge valve
Possible Causes
- 1.Gas cap
- 2.Cracked EVAP lines
- 3.Purge or vent valve not sealing
- 4.Canister damage
- 5.Filler-neck issues
Wiring & Circuit Notes
Purge and vent valve circuits.
DVOM Specs & Sensor Tests
Fuel-tank pressure sensor during monitor. Smoke-test results.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
4 steps locked behind Technician Mode- 1Step 1 — Gas Cap Inspection and Replacement if Needed: Inspect and replace the gas cap if the seal is damaged or the cap is loose.
- 2Step 2 — Smoke-Test the System: Smoke-test the EVAP system at low pressure.
- 3Step 3 — Command and Test Purge/Vent Valves for Sealing: Command and test purge and vent valves for proper sealing.
- 4Step 4 — Repair the Leak Source: Repair the identified leak source.
- 5Step 5 — Verify Monitor Completion: Verify the EVAP monitor completes on a drive cycle.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Typical Repair Costs
Gas cap $15–40; lines $20–200; valves $80–300; canister $100–400.
Related Codes & Pages
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Summary
Use the AI Diesel Tech diagnostic engine to run this code through a structured, evidence-gated sequence and get a confirmed root cause before any parts are replaced.