What Does a Smog Check Consist Of?


During the past decade, concerns about the negative effects of vehicle emissions on the environment have increased. Every vehicle on the road is required by law to undergo a smog emissions diagnosis to ensure the emitted gases meet state regulations. One of three tests will be implemented on a vehicle to ensure that it meets emission requirements.

The Different Tests for a Smog Check

  • Depending on the age of the vehicle, a standard smog check will consist of a test that monitors specific gas outputs, tail pipe emissions or computer diagnostics. ASM2, OBD2 and TSI are the three types of smog checks that are used to test vehicles.

ASM2 - Acceleration Simulation Mode 2

  • The Acceleration Simulation Mode 2 measures exhaust emissions for levels of gases like hydrocarbon, carbon monoxide, and nitrogen oxides. Car movement is simulated using a dynamometer, which replicates traction with a "treadmill-like" device, while a five-gas analyzer tracks emissions.

TSI -Two Speed Idle

  • The Two Speed Idle emissions test is used to check the smog output on vehicles at high and low speeds. This test measures the tailpipe exhaust emissions while the vehicle maintains certain speeds.

ODB2- On-Board Diagnostics Second Generation

  • The On-Board Diagnostics Second Generation is a system that triggers the service engine dashboard light whenever an emissions malfunction is recognized. During a smog check the servicemen will tap into the vehicles diagnostic link connector and be able to pinpoint where the malfunction has occurred based on stored information.

Smog Checks are Vehicle Specific

  • TSI and ASM2 are used for vehicles registered before 1995. OBD2 is used to check emissions by reviewing data taken by the computers in newer vehicles.

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