EVAP Failed by Smog Station Passed by Different Shop

So my vehicle with 165,000 miles went into a smog test / repair facility and passed everything but the evap test. I made the mistake and assumed all shops gave free retesting and I was wrong. This shop would give a free test if they did they repairs but would charge me for another test I did the repairs. So feeling uncomfortable with the shop and their explanation of $150 diagnostic fee ( when they just told me it was a problem with my gas lines with in a 4 foot section most likely ) and since I was told if I did the repairs I had to pay for another inspection I went to another smog facility. My vehicle passed everything the first time no problems.

So my question is it common for vehicles to have a "bad" day and just fail a smog evap test and then a few days later pass the "evap" test no problem?

Seems sketchy - if not on the original shops part then on the entire State's program if the same car can fail and pass at 2 different stations without any work being done.

In follow up - I feel compelled to file a complaint but don't want to take the chance my vehicle goes under stricter scrutiny and fails smog tests that will be way more costly or unrepairable.

Answer:

Your vehicle should have had similar EVAP (LPFET) results at both smog stations. The only thing which could have possiblely made a difference in test results could have been if the fuel tank level was higher during the second test; assuming if you had filled up between smog checks.

With more fuel in the gas tank, and less space to fill NOx (nitrous oxide is filled in the gas tank during the EVAP test in order to measure pressure drop), it is possible pressure build-up in the tank during the LPFET test was high enough not to cause a failure. If this was not the case (you had not filled up the gas tank between smog inspections), we can not speculate on why your vehicle failed at one station and passed at another. The EVAP test is fairly straight forward, and should be administered identically at all smog test stations.

posted by SmogTips Support