EVAP leak diagnosis for a check engine light cost: shop vs. mobile mechanic

EVAP leak diagnosis (smoke test) for a check engine light: estimated U.S. average labor cost at a repair shop and with a mobile mechanic. Diagnostic time only; the repair itself is extra. Estimates, not quotes.

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What the estimate covers

Diagnostic time only: reading the codes, checking the gas cap and filler neck, commanding the EVAP valves with a scan tool and smoke-testing the fuel vapor system to find the leak. The repair (gas cap, purge or vent valve, hose, charcoal canister, filler neck) is extra. Before paying for a test, check that the gas cap is tight and its seal is not cracked or missing: a loose or bad cap is a common cause of small-leak codes, and the light can take several drive cycles to go off after the cap is fixed. A flashing check engine light usually points to a severe misfire, not an EVAP leak: limit driving and have it checked promptly. Many shops charge a flat diagnostic fee instead of by the hour; small or intermittent leaks take longer to find.

Labor hours used: 0.5–1.5 h (typical 1 h), our own editorial estimate (not taken from a licensed labor guide).

How these estimates work

• Labor hours (Mechanic Notes estimate): each job has our own editorial "typical labor hours" range. Real times depend on the vehicle, engine and condition, and are not taken from any licensed labor guide.
• Shop labor rate (assumption): $100–$139/hour, the band where about half of surveyed U.S. general repair shops put their average labor rate (PartsTech / OEC U.S. General Auto Repair Shop Survey (about 700 shops, Sept 2025), as reported by Ratchet+Wrench), scaled by your area's mean wage for automotive service technicians divided by the U.S. mean ($27.13/h; BLS Occupational Employment and Wage Statistics, May 2025, SOC 49-3023; verify on bls.gov). States and metros without wage data use the next-wider area.
• Average shop cost = typical hours × estimated shop rate. The headline number uses the middle of both ranges (or a job’s stated typical hours, where the usual job sits near the low end); the range uses low hours × low rate to high hours × high rate. Rounded to $5.
• Average mobile mechanic cost = shop labor × 1.5 (mobile convenience premium: travel and convenience are built in). This is a default assumption, not a survey result.
• Parts are not included. Parts prices vary too much by vehicle and brand to estimate honestly here; price parts separately.

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Page last updated 2026-10-29.