What is the Emissions Test for Texas Vehicle Inspections?

Does Texas Require Emissions Testing?

Types of Emission Tests

An emissions test involves a preliminary inspection of different components of your car to ensure that they are functioning properly. This also includes a visual examination of the gas cap and dashboard lights.

Then, specific procedures are performed to evaluate its emissions and determine if the vehicle’s emissions are within its limits.

When it comes to emissions inspections, there are a variety of tests that a vehicle might have to pass. Three main testing methods are used depending on the specific county and the vehicle type.

What is OBDII

The On Board Diagnostics-Second Generation (OBDII) is a computerized mechanism found in vehicles from 1996 onward. It oversees the emission-related parts and ensures they're functioning correctly. Through the vehicle's internal computer, OBDII observes all emissions-related parts and systems.

The OBDII identifies faulty components or systems early, preventing significant failures and often alerting the driver before they even notice an issue. This early detection allows vehicle owners to address problems promptly, saving on potential high repair costs.

OBDII assessment is conducted with a scan tool that connects to the vehicle's computer, checking the integrity of the emission system and its components. The scan retrieves stored data from the computer, pinpointing malfunctioning emission parts or systems.

If there's an emission control issue, a dashboard indicator, such as "Check Engine" or "Service Engine Soon", will light up. When the OBDII spots a malfunction, it logs a specific diagnostic trouble code (DTC) in the computer. A technician can then use an OBDII scanner to access these codes, swiftly identifying the issue and rectifying it before it escalates.

What systems are checked during the OBDII test? Well, the On-Board Diagnostics (OBDII) emissions evaluation for vehicles from 1996 onwards encompasses three primary checks:

#1 Malfunction Indicator Lamp (MIL) Test: This stage involves examining the Malfunction Indicator Lamp (MIL) or the "Service Engine Soon" light.


#2 Assessment of MIL Command Status & Diagnostic Trouble Codes (DTCs): If the MIL command status is ON, it means the vehicle's Powertrain Control Module (PCM) is signaling for the MIL to illuminate due to an identified issue within the OBDII system.

#3 Review of OBDII Non-Continuous Readiness Monitors: These monitors function as self-assessment tools for each emission-related component, such as the EGR, O2 sensor, among others.

Here are other emission test types:

  • Acceleration simulation mode (ASM) test. Cars manufactured in 1995 and older have to undergo the Acceleration Simulation Mode test, which is an updated version of the older two-speed idle test. However, both these tests are tail-pipe based, so they analyze your vehicle’s emission levels while it's running. During the ASM test, also known as a “treadmill test,” the vehicle is inspected under simulated driving conditions with the help of a dynamometer. The ASM measures CO2, NOx, HC, and CO levels under average driving conditions and acceleration.
  • Two-speed idle test. During this test, a technician inserts a probe into the vehicle’s exhaust pipe to measure the engine speed using a tachometer. Then, there are two test sequences: an idle test and a 2500 RPM test. The technician measures the vehicle’s exhaust emissions (CO2, HC, and CO) in both these states.

An emissions test is a procedure that examines the vehicle’s emissions and ensures that it does not increase the level of air pollution or affect air quality. In other words, it is a smog check of your vehicle.

Which Vehicles Must Pass The Emissions Test in Texas?
  • Currently, all gasoline-powered vehicles manufactured prior to 1995 (or upon expiration of the two-year initial inspection sticker) must undergo an annual emissions test.
  • Starting in 2025, vehicles registered in designated counties in Texas must pass the emission test.
Which Vehicles are Currently Exempt From the Emissions Test in Texas?
  • Motorcycles and diesel-powered vehicles do not require the emissions test
  • Vehicles manufactured in the last two years
  • Electric vehicle(EV)
  • Cars that were made more than 24 years ago
  • Farm machines
  • Road-building equipment
Texas Counties that Require Emissions Testing
  • Brazoria
  • Collin
  • Dallas
  • Denton
  • Ellis
  • El Paso
  • Fort Bend
  • Galveston
  • Harris
  • Johnson
  • Kaufman
  • Montgomery
  • Parker
  • Rockwall
  • Tarrant
  • Travis
  • Williamson>
Enhanced Vehicle Emissions Tests

Basics of Emissions Testing in Texas

Texas residents have 90 days to register their vehicles. This process includes the annual vehicle safety inspection, emissions test (if required), and vehicle registration renewal.

Vehicle owners are required to bring their vehicles to an inspection station certified by the Department of Public Safety (DPS), pay a fee for testing, and provide proof of insurance.

In Texas, the cost of a smog check is regulated and varies from $11.50 to a maximum of $24.50 for any of the three main testing methods.

A vehicle safety inspection costs $7, and the combined fee for both inspections cannot exceed $31.50, although the exact amount will depend on the testing area and vehicle engine type.

What If I Don’t Pass My Emissions Test?
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