6 Key Factors to Passing a Smog Check

6 Key Factors to Passing a Smog Check

Smoke inspections are essential to comply with environmental safety regulations and to ensure that vehicles are in proper operating condition.

Vehicles (especially older or idling vehicles) may be difficult to subject to a smog check for the following reasons:

Repairs are required
Never submit a vehicle in need of major repairs for a smog check, as this may result in a failed inspection. The vehicle must be completely repaired before it can receive a smog check.

Insufficient Oil Quality
If the oil has not been changed within the last 5,000 miles, the engine oil may be in poor condition at the time of the smog check. High levels of hydrocarbons caused by an untimely oil change can result in a failed smog test.

Insufficient engine temperature
Passing an emissions test requires optimal operating temperatures. The vehicle needs to be driven for at least 20 minutes before undergoing a smog test. This provides ample time for the coolant, oil, and catalytic converter to warm up to and maintain acceptable temperatures as specified by the emissions test.

Recently Replaced or Disconnected Battery
If the battery is replaced or disconnected, information about the vehicle’s driving cycle may be lost. If the internal self-test monitor is not present, the smog check cannot be cleared. Therefore, before checking the vehicle’s smog system, drive approximately 100 to 200 miles in a week to reset or complete the emissions monitor.

Check Engine Light (CEL) Performance
If the CEL light is on, the smog test will automatically fail. However, according to California law, having the CEL light on is not an excuse to forgo a smog test. Have the emissions serviced at a certified repair store so they can use their tools to retrieve the trouble codes from the ECU (Engine Control Unit) and make the necessary repairs to turn off the CEL.

Insufficient Tire Pressure
As part of the smog check, all pre-1999 models are dyno tested. The only way to improve driving stability and control during the emissions test is to provide adequate tire pressure as specified by the vehicle manufacturer. Therefore, make sure your tires are fully inflated before stopping for a smog check.


Why is a smog check critical?
Smog checks may seem unimportant compared to many of the other maintenance requirements to keep your car in good working order, but they actually go a long way toward protecting the environment. Smog checks ensure that your car is safe for passengers and other drivers, and can detect problems with air filtration, gas cap leaks, malfunctioning oxygen sensors, and a host of other issues. The biennial model is designed to support California’s daily goal of eliminating 100 tons of smog emissions through these inspections.

With smog testing, these problems can be detected early and addressed before they get worse. Beyond the risks, smog testing improves fuel economy and helps drivers consistently maximize vehicle performance.

Does my vehicle meet the requirement for a smog test every two years?
In most cases, if you’re required to have a smog test, you’re probably getting ready to sell your vehicle. hybrid vehicles manufactured in the mid-1970s and later are also required to have regular smog tests, but vehicles less than four years old don’t even need to have a smog test if there’s a change in ownership.

How can I make sure my car passes the smog test?
Make sure all warning lights are out or fixed before the inspection. Smog tests often fail for check engine lights, and these tests must be passed after the vehicle has been driven 100-200 miles. Muffler problems are another common reason for failed inspections and may require additional financial support from the owner.