Difference between a Smog Check and a Test Only Check
By Theydiffer - June 13, 2015

The two terms in question, a smog check and a test only smog check, may seem to be similar as they both revolve around the idea of “smog”, but on closer analysis, this article will prove that these two concepts bear very distinct meanings.


A smog check is a test that is done on the exhaust system of a motor vehicle to determine how many pollutants, and of which type, the vehicle is emitting.

A test only station can only smog test vehicles and is not allowed to perform any automotive repairs.

Comparison chart

Smog checkTest only
Involves inspection of motor vehicle exhaust system and other necessary partsThe tests carried out here are strictly on the exhaust system and nothing more.
Any vehicle can be prescribed for a smog check even without suspicions of causing pollution.For a vehicle to be prescribed for the test only center there must have been a failed smog inspection test previously.
A smog check station can perform additional repairs on clients’ motor vehicles.It can also perform the function of diagnosis of the inspected vehicles’ faults.A test only station is not allowed to perform any repairs.This station however is not allowed to comment or make any diagnosis.

Smog Check vs Test Only Check

What’s the difference between a smog check and a test only check?

A smog check includes an assessment of other parts of the vehicle to make sure that they are in good working condition. This is mostly done on the parts that are related to the motor vehicle’s emissions control.

A test only center is expected to ensure a non-biased smog test inspection. Vehicles that are prescribed for test only centers most likely will have the characteristics of failing a previous smog inspection test by recording high emission readings that would normally classify them as gross polluters, or those that are deemed by the Bureau of Automotive Repair as having high chances of failing a smog inspection.

A test only station is also prohibited from performing or commenting on any diagnosis or even on any possible required repairs.

A smog check is relatively more expensive than a test only visit because a smog check center carries out general diagnosis of the motor vehicle and could extend to offering minor or major repairs on automobiles, hence accruing costs, whereas a test only center is restricted only to exhaust emission levels and therefore this is the only service their clients get to pay for.