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Check engine light is on. Took to replace gas cap and 55 miles later MIL came back on. Was told a smoke test is the thing to do. p0456. small evap leak. 1) what is an appropriate cost for smoke test? 2) Is it hard to find a small evap leak using a smoke test? 3 Is there an alternative to a smoke test?

Answers from the Automotive Experts

Jessica Howe, Automotive Expert & Coach at


All pricing for services and tests is going to vary depending on where you live, the number of qualified technicians around you, and what you drive. While we generally cannot give you pricing information, you can expect to pay around $100, give or take $50. You can also buy cans of "smoke" and other devices and attempt a test at home if you feel capable of doing so. 

It is not hard to find a small EVAP leak when performing a smoke test. You have to take your time, be patient, and pay attention. Some leaks, such as those from a worn hose or physical damage, can be seen without performing a smoke test. Smoke tests are used when you cannot find the leak otherwise.

Smoke tests, and dye tests in fluid systems, are thought of as a final resort to some extent. If you visit a technician with the right tools, they can manipulate the EVAP system with a scan tool and may be able to diagnose it that way as well. 

Good luck!

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