Smog checks are essential not only to ensure the proper working condition of the vehicle but also to adhere to environmental safety rules.

Vehicles, especially older models or ones that are left idle, can potentially run into issues with smog checks because of the following factors:

1. The Need for Repairs

Trouble Starting the Engine

Never subject a vehicle requiring major auto repairs to a smog check as it is bound to fail the test. A Vehicle needs to be completely repaired prior to bringing it in for a smog inspection.

2. Poor Oil Condition

Inadequate Engine Temperature

The engine oil condition can be catastrophic in a smog check when the oil hasn’t been changed for the last 5,000 miles. Inadequate oil changes will result in a high concentration of hydrocarbons and will definitely fail the smog check.

3. Inadequate Engine Temperature

Trouble Starting the Engine

Optimum operating temperatures are vital in order to pass the emission test. A vehicle should be driven for at least 20 minutes prior to being taken in for a smog check. This gives the coolant, oil, and the catalytic converter enough time to reach and remain at the temperature recommended by emission test standards.

4. Recent Change of Battery or Disconnection

Change of Battery or Disconnection

With a change in the existing battery or owing to disconnection, the data related to the ‘Driving Cycle’ of a vehicle will most likely be lost. In the absence of internal self-test monitors, a smog check can never be cleared. To do so, drive for around 100-200 miles for one week to reset or complete the emission monitors before getting smog inspected.

Also Read – California Smog Check Rules: What You Need to Know

5. Status of the Check Engine Light (CEL)

What Does Check Engine Light Mean

An illuminated CEL will result in an automatic failure in the smog test. However, as per the California State Law, a switched-on CEL is no reason to avoid a smog check. Visit a certified emission repairs shop so they can use a trouble code retrieval tool which will extract trouble code data from the ECU (Engine Control Unit) and perform necessary repairs, turning the CEL off.

6. Inadequate Tire Pressure

Inadequate Tire Pressure

All vehicle models that are older than 1999 are tested on a dynamometer while undergoing smog checks. Only an adequate tire pressure, as required by the vehicle manufacturer, will ensure greater stability and control while driving during the emission test. Therefore, make sure your tires are adequately inflated before pulling in for a smog check.

Why are smog checks important?

Smog checks may seem secondary to the variety of other maintenance necessities to keep your vehicle properly maintained, but smog checks go a long way for preserving the environment. They ensure that your vehicle is safe for its occupants as well as surrounding drivers, which can uncover a variety of issues with air filtration, gas cap leaks, oxygen sensor malfunctioning, etc. In California, there is a daily goal of 100 tons of smog emissions being removed via these inspections, which is built to be sustained through the biennial model.


Through smog checks, these issues are uncovered early and are able to be addressed before they become more dangerous. On top of dangers, your fuel efficiency can be tackled in a smog to benefit the driver in getting the best possible output for their vehicle on a regular basis. 


Does my vehicle meet the requirements to have biennial smog checks?


Most often if you’re looking for a smog check, you may be preparing to sell your vehicle. Otherwise, for a smog check to be necessary for a vehicle, the model must be eight years or older. Hybrid vehicles that are mid 70s or newer must also have consistent smog checks, and any vehicle under four years of usage doesn’t require a smog check even in a change-of-ownership scenario.

How can I ensure my vehicle will pass a smog check?


Make sure that prior to inspection, all warning lights are unlit, or have been resolved since coming on. Check engine lights are common reasons for failed smog checks and will require 100-200 miles of driving following the check in order to pass. Muffler issues can also be a common reason for a failed inspection and may require more intensive financial care from the vehicle owner.


Also Read – The Common Signs of a Bad Air Filter


A-Z Tech Automotive is always ready to help. Call us today at (949) 472-8111 for car repair and maintenance. You can also book an appointment online to schedule vehicle maintenance and repair service with us.