EVAP Control System Problem During Smog Test

Nearly all vehicles need to go through a smog test to be legally registered with the DMV in California. But while the test is painless and quick, a lot of cars still end up failing. If you have ever been in this situation, you know that it can be quite stressful, and nearly always requires a trip to your mechanic.

Luckily, a lot of times the reason why your car failed its smog test can be easily identified, and just as easily fixed and repaired. More often than not, the fault occurs because of either old and dirty air filters, broken sparkplugs, cold engines, or faulty check engine lights. The good news about all of these is that all of these can be quickly fixed, and quite cheaply too.

However, you do not even need to be worried about taking your car to the mechanic and getting all these components checked out.
Just come on down to San Jose Smog check and get your car inspected. There is only a 10 percent chance of it failing the test, and in case it does, our experienced technicians will tell you exactly what the problem is.

You can simply fix that, and come back within the month for a free retest and drive a legally registered car.

Unfortunately, there is one reason for a failed smog test which is quite difficult to diagnose and can be quite costly to repair as well. This is none other than a defective EVAP control system, which we will be discussing in detail below.

What is an EVAP control system?

The EVAP control system, or the Evaporative Emissions control system has a very specific purpose. It stops the fuel vapors in your gas tank and fuel system from escaping out of your car, and into the atmosphere.
Why? Because these gasoline vapors contain a lot of hydrocarbons, which are bad for health, and can cause a lot of smog. Thus, if you have a damaged or leaking EVAP system, there is a very high chance that you will fail your smog check.

How can the EVAP system get damaged?

There are a lot of reasons why your EVAP system may get damaged. The system itself consists of a charcoal canister which stores all evaporated gas vapors until they are required by the engine to run your car. It also contains a large number of hoses, vents, and valves which control the flow of fuel vapors into your engine.

Many of these hoses and vents are brittle, and can easily develop leaks and small cracks over a long period of time. It is also possible that one of these vacuum hoses has become loose, or even disconnected, which is releasing gas vapors into and out of your car.

Similarly, it is also completely possible that the charcoal cannister itself has gotten cracked, which will only worsen every time you drive over a pothole or bump your car in something. However, the most common and the most overlooked cause of a faulty EVAP is a leaky or loose gas cap.

How do I Identify an EVAP leak?

Luckily, there are a few ways of identifying whether or not you need your EVAP control system looked over before you come for your smog test. The most basic measure is to look at your check engine light. If it is blinking, there is a chance that your car’s computer has detected a change in pressure in the EVAP system, which could indicate a leak.

A second way to identify a leak in your EVAP system is to take a good long sniff in your car. If your nose can detect a faint smell of gasoline, it is likely that there may be a small leak in there somewhere. But if you can definitely smell gasoline, and your check engine light is blinking, you should definitely get your car checked out.

The last method to identify a potential problem with your EVAP system is to look at your gas mileage. If you can see a sudden decrease, it unfortunately means that your car may be wasting gas vapors due to leaks. And while any single indicator does not mean a faulty EVAP system, all of them together is bad news.


If your car is due for a smog check, be sure to check for any indications of a faulty EVAP control system. If you think that your EVAP system needs looking over, make sure that you visit your mechanic before coming down to San Jose Smog Check to get your car tested by some of the best, star certified technicians in California.