Can You Pass a Car Inspection With The Check Engine Light On?

Technically, no, your vehicle cannot pass an emissions inspection if the check engine light (CEL) remains on during the test. The real answer? It depends on your state and county motor vehicle laws, your vehicle’s age, gross weight and how many miles it’s been driven since its last inspection

According to Jon Stull, a certified vehicle emissions and safety instructor in Pennsylvania, even if a vehicle in his state passes a safety inspection, it’s illegal to affix a safety inspection sticker to the windshield if the vehicle fails an emissions test. He adds this is “one of the most difficult regulations to explain.”

What Is a Car Inspection?

Vehicle inspections are regulated by individual states, with most requiring two types:

• Safety inspections: These include brakes, steering and suspension, tires, exhaust, lights, etc. It ensures a vehicle is roadworthy and safe to operate.
• Emission inspections: This determines if the emission control systems are operating properly, with tailpipe emissions measured for excess smog levels. Emission inspections are performed to reduce harmful exhaust greenhouse gases.

Inspection requirements differ by state. Some require both inspections; others require only one, or none. Some states demand vehicles pass a safety and emission inspection before they can be registered. Others require proof of insurance before the inspection.

Before insuring a vehicle, some insurance companies may insist on pre-purchase inspections to identify potential problems, especially with older vehicles or salvaged flood cars. Check with your state Department of Motor Vehicles (DMV) to determine which, if any, inspections are required.

Note: For peace of mind, always get an independent pre-purchase safety and emission inspection before buying a used car.

Who Does Emission Inspections?

It depends on the state. New York and Pennsylvania certify independent repair shops and mechanics to perform emission inspections and repairs. Arizona runs its own emission testing stations. Check with your state DMV to determine where to go and who can perform an emissions inspection.

What Happens During an Emission Inspection?

Depending on the state, region and vehicle year, an emissions inspection and maintenance inspection (I/M) may include visual anti-tampering, onboard diagnostic (OBD) and/or tailpipe idle tests.

During the anti-tampering inspection, a visual examination ensures all emission components are in place, working and have not been altered. Depending on the state, inspectors check the following items:

• Catalytic converter;
• Exhaust gas recirculation (EGR) valve/system;
• Positive crankcase ventilation (PCV) valve/system;
• The air pump, its valves, pulleys and fan belts.
• Evaporative control system canister, canister filter/system;
• Fuel lines and gas cap.

During an OBD test, your vehicle will link to the emission testing equipment via the on-board diagnostic link connector (DLC). It checks:

• Readiness monitor status (the emission system’s self-test, self-diagnostic system), ensuring the OBD system is functioning properly.
• The CEL is on with the engine off and key on, and is off while the engine is running.
• The OBD system for diagnostic trouble codes (DTC).

Exhaust gases measured during the tailpipe idle test:

• Hydrocarbons (HC);
• Carbon monoxide (CO);
• Oxides of nitrogen (NOX);
• Oxygen (O2).

On average, an emissions test should take between 15 and 30 minutes.

Some states follow California’s stringent emissions I/M standards, while others adopted the U.S. Environmental Protection Agency (EPA) Vehicle Emissions Inspection and Maintenance I/M standards.

When a vehicle fails an I/M test, the inspector issues a report. Unless the inspector is a state-certified I/M repair technician, they aren’t obligated to diagnose or suggest what repairs are necessary to pass the inspection. Otherwise, your mechanic (or you!) will need to determine why the vehicle failed the emissions inspection.

Anyone, including the vehicle owner, can make the repairs.

Is an Illuminated Check Engine Light an Automatic Fail?

Yes. The OBD test on 1996 or newer models verifies proper CEL function. If the CEL is on with the engine running, it automatically fails an emissions inspection.

However, there are exceptions, exemptions and waivers to every rule. Depending on the state, these could include:

• Vehicles older than 20 years old;
• Senior citizens with vehicles 10 years or older;
• Number of miles driven since the last emissions inspection;
• Non-traditional vehicles like classic cars, antiques and parade vehicles;
• Making and documenting repairs trying to correct the problem. You can request a one-year waiver if the vehicle fails a second time.
• Reinspected, failing the OBD test again, but passing safety inspection.
• Vehicles less than four years old (depending on the state) can pay a smog abatement fee.

Again, check with your state DMV to determine if your vehicle may be eligible for an exemption or waiver.

What To Do if Your Check Engine Light Is On

There are several easy DIY steps you can attempt to turn off the CEL.

First, make sure the gas cap is tight. You can also try disconnecting the battery for five minutes. An inexpensive code reader/scan tool may also turn the CEL off.