In Travis and Williamson Counties, emissions testing is a mandatory part of State (vehicle) Inspections.

Emissions Testing Procedures

Is your vehicle required to be emissions tested?
All Texas registered vehicles are required to receive an annual inspection. All inspections include a comprehensive safety inspection; however, some vehicles are required to have an emissions test in addition to the safety inspection.

Which vehicles are required to have the emissions test?

  • Vehicles registered in designated counties. Designated counties include: Brazoria, Fort Bend, Galveston, Harris, Montgomery, Collin, Dallas, Denton, Ellis, Johnson, Kaufman, Parker, Rockwall, Tarrant, Travis, Williamson and El Paso counties.
  • Gasoline powered vehicles. Diesel powered vehicles and motorcycles are exempt from emissions testing, but are still required to have the annual safety inspection.
  • Vehicles 2 through 24 years old OR upon expiration of the two-year initial inspection sticker.

inspections map


What Type Of Emissions Test Will My Vehicle Need?

El Paso, Travis and Williamson County Motorists
In conjunction with the annual safety inspection, all gasoline powered vehicles from 2 through 24 years old which are registered or primarily operated in emissions counties will be subject to one of the following emissions tests.


1995 and older vehicles will receive the Two Speed Idle (TSI) test while 1996 and newer vehicles receive the On-Board Diagnostic (OBDII) test.

service-image-emissionsWhat if your vehicle fails the Emissions Test?

Round Rock Muffler and Automotive is a State of Texas Recognized Emissions Repair Facility.  We can make whatever repairs are necessary to bring your vehicle up to the required emissions standards.

State of Texas “Aircheck Drive a Clean Machine” program

dacm1The AirCheck Texas Drive a Clean Machine is a program to remove older, more polluting vehicles from Texas roadways in emissions counties.  If your vehicle is over ten years old or has failed emissions tests, these programs may help you with the cost of repairs.

Click on the box below to learn more about this program and whether it may apply to you.  Learn More

Catalytic Converters

catalytic converter is central to controlling your auto emissions quality.  It uses a catalyst to convert three harmful compounds – Hydrocarbons, Carbon Monoxide, and Nitrogen Oxides – in car exhaust into harmless compounds.   It converts hydrocarbons to carbon dioxide and water, nitrogen oxides into nitrogen and oxygen, and carbon monoxide into carbon dioxide.  In some situations a catalytic converter can be repaired. Most of the time replacement is the only option.