• Top 7 Reasons Why your Car Failed the Smog Check

Top 7 Reasons Why your Car Failed the Smog Check

Top 7 Reasons Why your Car Failed the Smog Check Image

You must pass the smog check in Rancho Cucamonga and other places in California. You may visit us for the same or any other authentic center as a smog check is mandatory to register your vehicle.  

The design of a smog check from us is such that we can effectively check the emission levels of your car and its exhaust system. Through the test, we can check the levels of carbon monoxide, hydrocarbons, and nitrogen oxides that are emitted from your vehicle. 

Whenever your vehicle has levels exceeding the permissible amount, you are bound to fail the smog test. Usually, this happens as your car is running rough, faces engine problems, or necessitates repairs to the exhaust system. However, often there could be certain times when your vehicle may fail, and it doesn’t have anything to do with the emissions that are being discharged.  

In this article, we have identified the top seven reasons why your vehicle may not pass a smog check. What we have mostly experienced are as follows- 

Check Engine Light is On 

Whenever you find that your check engine light is on, your vehicle will fail the smog test in California every time. However, according to California state law, a car repair shop can’t turn you away only because your check engine light is on. In such circumstances, they will test your vehicle and you will fail. So, when your check engine light is on, bring it to the nearest car repair center. Tell them to do the necessary repairs and ensure that the light is shut off before going for a smog check.

Untidy Air Filter 

When your air filter is dirty, the combustion chamber cannot get sufficient air. So, you will have an excessive amount of carbon discharged in your exhaust. This will lead to a situation where your automobile will fail the smog check in our authorized smog test centers in California. Generally, replacing the air filter will solve the problem. 

Your Car is Not Fully Warmed Up 

Another common reason why your vehicle may not clear the smog test is due to your car not being fully warmed up. We recommend that you drive your vehicle for 20 to 30 minutes before bringing your car to us for a smog check. This lets your car reach the adequate fuel mixture level and combustion levels. Both of them can throw off the emissions levels of the vehicle.  

The battery was Recently Disconnected or Replaced 

If you disconnect or replace your battery, you can throw off the internal test monitors that are checked within your car during a smog test. Whenever you have recently disconnected or replaced your battery, we suggest you drive your car for at least 100 miles and wait at least a week before we run a smog check on your vehicle.  

The vehicle Needs an Oil Change 

An extremely valid reason why your vehicle may fail a smog check is that it needs an oil change. When the oil in your vehicle becomes dirty, the engine breathes in some of these dirty fumes. Then, it may give higher emissions readings during a smog test because of these fumes. Replace your oil before a smog check and then wait a few days before the test of your car.  

Poor O2 Sensor 

Whenever your oxygen sensor is poor, your vehicle may not clear the smog test from us as it is discharging excessive carbon in the exhaust. The O2 sensor reports the oxygen levels in the exhaust. When the data is inaccurate, the engine control module may put excessive fuel in the combustion chamber. 

Damaged Catalytic Converter 

You won’t clear a smog check from us when the catalytic converter turns out to be a faulty one. Other symptoms that the catalytic converter is going haywire include rotten egg odors and an overheating engine. You must get the catalytic converter replaced right away during smog service in Rancho Cucamonga from us because this will be the exhaust part that is dealing with carbon monoxide. 


You need to have all repairs made to your car before having a smog check. If you are preparing to have your car smog checked, bring it to an authentic auto repair shop, that will scrutinize your vehicle, make any necessary repairs and make it ready for a smog check. This will help you to increase the chances of you passing from us. Book your appointment for a smog test with us today.