A car fails inspection primarily due to safety and emissions issues that fall outside state-mandated standards. The most common reasons are illuminated warning lights (like the check engine light), faulty brakes, excessive exhaust emissions, malfunctioning lights, and worn tires. Addressing these specific, measurable problems before the test is the most effective way to pass.
The check engine light is a top culprit. This light indicates the car's computer has detected a problem affecting emissions. Common triggers include a loose gas cap, a faulty oxygen sensor, or a malfunctioning catalytic converter. A diagnostic scan is necessary to identify the specific trouble code.
Brake system failures are critical. Inspectors measure brake pad thickness and rotor condition. Most states require a minimum pad thickness, often around 1/8 of an inch. They also check for brake fluid leaks and ensure the parking brake functions correctly.
Emissions test failures occur when pollutant levels (hydrocarbons, carbon monoxide, nitrogen oxides) exceed limits. This is often linked to a faulty oxygen sensor, a clogged air filter, or a failing catalytic converter. Regular maintenance, like oil changes and spark plug replacements, helps prevent this.
Lighting and visibility issues are simple fixes but common failures. Every exterior light—headlights (high and low beams), brake lights, turn signals, and license plate lights—must be operational. Cracked windshields, especially if the damage obstructs the driver's view, will also cause a failure.
Tire condition is a major safety check. Inspectors look for adequate tread depth. The legal minimum in most states is 2/32 of an inch. You can check this with the "penny test" (insert a penny into the tread with Lincoln's head upside down; if you can see the top of his head, the tread is too low). They also check for visible damage like bulges or cuts.
| Common Inspection Failure Points | Typical Standard/Cause | Preventive Action |
|---|
| Check Engine Light | On (indicates emissions-related fault) | Get a pre-inspection diagnostic scan. |
| Brake Pad Thickness | Below 1/8 inch (3.2 mm) | Visual inspection and measure before test. |
| Tire Tread Depth | Below 2/32 inch (1.6 mm) | Perform the penny test regularly. |
| Exhaust Emissions | Exceeds state-specific limits for CO/HC/NOx | Ensure proper oil changes and engine maintenance. |
| Windshield Damage | Crack in driver's line of sight (>6 inches) | Repair or replace damaged glass. |
| Headlight Function | One or both beams not working | Check all lights before driving to the inspection station. |
| License Plate Light | Bulb is burned out | Perform a simple walk-around check at night. |
