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Vehicle Inspection

The Missouri Department of Revenue (DOR) requires Missouri residents to complete regular vehicle inspections.  The motor vehicle inspection required involves two parts:

  • Vehicle safety inspection
  • Smog check and emissions testing

Various parts of your vehicle will be inspected by technicians.

If you fail inspections or neglect to have them completed, you car cannot be legally registered in the state of Missouri, making it illegal to drive it.

Vehicle Safety Inspection

The Missouri Vehicle Safety Inspection Program is regulated by the State Highway Patrol (MSHP).  The purpose of the program is to ensure that your vehicle does not pose a threat to you, your passengers, or other drivers on the road, and that it adheres to Missouri safety laws.

Various parts of your vehicle will be inspected by technicians, including:

  • Seat belts
  • Windshield and windows
  • Turn signals and headlights
  • Brake lights
  • Brake system
  • Horn
  • Steering mechanism
  • Rearview mirrors
  • Exhaust system
  • Fuel system
  • Tires and wheels
  • Bumpers
  • Airbags

Once you successfully complete your inspection, an inspection sticker will be affixed to your windshield where it must be displayed at all times.  You will be given a Certificate of Inspection and Approval, which will be required for registering and/or renewing your registration with the Missouri (DOR) Department of Revenue.

Smog Check and Emissions Testing

An emissions test is a test conducted on vehicles to check for pollutant emissions produced by the engine of a car.  There are generally specific standards a vehicle must pass to be cleared from the emissions test.  However, there are times when an engine fails this test.  Some of the common reasons for failing an emissions test:

Fuel metering out of specification
There are several factors that can cause a fuel metering of your vehicle to be out of specification. It may be due to a faulty computerized engine control, carburetor, or fuel injection unit.

Faulty oxygen sensor
The oxygen sensor in a vehicle measures the amount of oxygen in the exhaust gas.  A faulty or defective oxygen sensor is not uncommon and can be caused by several things.  A faulty oxygen sensor can lead to other problems including overheating, higher toxic emissions and loss of acceleration power.

Defective ignition system
This means that during an HC check, the analyzer detects high Hydrocarbons.  If the vehicle is not properly maintained then expect to have an ignition system that is defective causing it to fail an emissions test.  The most common causes of high HC are defective spark plugs wires, worn out spark plugs, over advanced ignition timing or a worn out distributor cap.

Leaks in the vehicle’s vacuum
Vacuum leaks are another common reason for an emissions test failure.  A vacuum leak is often caused by the MAP sensor not working properly.  The MAP sensor measures the load of an internal combustion of the engine’s electronic control system. Leaks may be found in the gaskets or vacuum lines.

Rich fuel mixture
High CO2 levels are often caused by high carbon monoxide levels due to a weak ignition or a rich air/fuel mixture.  There are numerous causes of a rich fuel mixture.  A contaminated oxygen sensor, leaky injectors, and excessive fuel pressure are some common causes of richness to the mixture.

Malfunction in the air injection system
The air injection system helps reduce the emission of hydrocarbons and carbon monoxide of a car.  This happens by forcing fresh air into the exhaust of the engine.  If the air injection system is defective or malfunctions, the engine is not able to properly control the levels of hydrocarbons and carbon monoxide emission causing the car to emit high levels of these dangerous gases.

Faulty evaporative emission control system
Evaporative Emission Control System (EVAP) prevents gasoline vapors from the fuel system and tank from being released into the atmosphere.  Some of the more common causes of a faulty EVAP include leaks in the vacuum hoses and vents, defective purge valves, or faulty gas caps.

What can Dobbs do for you?

Dobbs Tire & Auto Centers is your best choice for having your vehicle safety inspection and smog check and emissions testing performed.  The staff of experienced ASE-certified service technicians is courteous and professional and committed to getting you in and out the same day.  Best of all, as a locally owned and family owned company since 1976, at Dobbs Tire and Auto Centers, you have the assurance of knowing that the Dobbs Associates will perform the inspections and tests accurately — and stand by their work.

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