Question

Can you pass smog with a check engine light on​?

No, your vehicle won’t pass a smog check if the check engine light is on. The illuminated check engine light implies an issue with the emissions system. If the check engine light is on, you must get the system inspected, repaired, and clear the light before the smog check.

A smog check is an emissions test that many states mandate to ensure that vehicles aren’t releasing unwanted pollutants into the air. This test aids in reducing air pollution. If your vehicle fails the smog check test, you will be unable to renew your registration until you resolve the issue.

Why is your vehicle’s check engine light on?

There can be many reasons why the light is illuminated. However, these are among the most common reasons that affect your vehicle’s emissions system.

• A defective oxygen sensor: A faulty oxygen sensor can lead to increased emissions and a decrease in fuel economy.
• Issues with the catalytic converter: If your vehicle’s catalytic converter is blocked or defective, it will emit higher pollutant levels. This turns on the check engine light.
• Loose or defective gas cap: A loose or defective gas cap lets the fuel vapors escape, causing trouble with the evaporative emissions system.
• Faulty Mass Airflow Sensor (MAF): This sensor helps control the quantity of air entering your vehicle’s engine. If the sensor is defective, it can cause an increase in emissions or a drop in engine performance, ultimately leading to a failed smog check test.
• Broken ignition coils or spark plugs: if your vehicle has faulty ignition coils or spark plugs, it can cause an increase in emissions, misfiring, or a decrease in fuel economy, ultimately leading to a failed smog check test.

How to fix your vehicle’s check engine light before the smog check test

• The ideal way to diagnose the issue is by doing a professional scan. A qualified technician may use an OBD-II scan tool to determine the issue that caused the light to illuminate.
• On finding the issue, perform the required repairs. This includes tightening the gas cap, replacing the oxygen sensor, or fixing an engine part.
• After doing the repairs, take a test drive of 50-100 miles to allow the OBD-II system to reset. The vehicle’s powertrain control module requires time to verify that the issue is resolved before the light turns off.
• Before going for the smog test, use the OBD-II scan tool to check if the vehicle’s readiness monitors are set. If not, your vehicle will fail the test again, even if the check engine light has been turned off. It is always best to fix issues with the help of a technician.