Like any test, the smog test is a scary proposition. Required every two years in some California counties and on vehicle resale statewide, smog checks have gone a long way in reducing emissions in this vehicle-obsessed state. But, that doesn’t reduce the angst when you drive into your local smog check station.
Passing a smog test is as easy as passing any test, as long as you come prepared. Here are some guidelines that should help you ace this test.
Make sure your vehicle is running well. If it’s missing, choking, belching smoke, get it to a repair shop before you go anywhere near that smog inspection bay. An appointment for a tune-up prior to your smog check can save you a lot of time and trouble, not to mention money.
Take the long route to your smog test. Vehicles run at peak efficiency when they’re warmed up, a condition that can be reached in less than 10 to 15 miles of driving. If possible, hit the freeway/highway on your way to the station, to help clear out the pipes.
Fresh gas, oil, correct tire pressure and fuel additives all play a part in acing this test. All of these elements can make small, but critical, differences the test outcome. If the vehicle’s been sitting for a long time, drain the gas tank (or run it to nearly empty) and refuel. Change your oil. Some mechanics recommend fuel additives. Additives clean carbon deposits in your engine's intake and exhaust paths, lowering emission levels and improving overall engine performance. On the tire pressure: some stations require the mechanic to drive the vehicle on the dyno; the stability and accuracy of even and correct tire pressure could make a difference in the test outcome.
Make sure that pesky “Engine Check” light is off. Depending on the age of the vehicle, the light probably means nothing, but to smog check technicians it means an automatic “fail.”
The last thing to be checked is the gas cap. Make sure it fits well and is tight.
If you think your vehicle will fail a smog check, have it pre-tested. Do this for two reasons. First, you don’t want those awful results on record and, second, if the failure is catastrophic, you will always have to have the vehicle smogged at a “Smog Check Only” station. Any repairs will then have to be done at a Test and Repair Station that records all work done.
With a pre-test, you can have your mechanic make the necessary repairs and adjustments then sail through the actual test.