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Check-engine light on? It will fail the Bexar emissions test

The Texas emissions test is an OBDII computer test. If your car's computer is commanding the check-engine light on with a stored trouble code, the vehicle fails. Find out why the light is on before you pay for a test.

What the OBDII test checks

According to DPS, the test has three parts:

Bulb check: the check-engine light must come on when the key is turned on and go off when the engine starts. A light that doesn't work fails.
Light command status and trouble codes: if the computer is commanding the light on and a diagnostic trouble code (DTC) is set, the vehicle fails.
Readiness monitors: the car's self-checks must have run. For 2001 and newer models, one "Not Ready" monitor is allowed and two or more fail. For 1996–2000 models, two are allowed and three or more fail.

Don't just clear the code and go test. DPS warns that clearing codes with a scan tool, or disconnecting the battery, resets the readiness monitors to "Not Ready." The car then has to be driven through a full drive cycle (mixed city and highway driving) before the monitors are ready again. Fix the problem, drive normally for a while, and check readiness before your test. DPS: Ready or Not

Step 1: read the code yourself (about two minutes)

Every 1996-and-newer car has an OBDII port, usually under the dashboard near the steering column. An inexpensive code reader plugs into that port and shows:

the trouble code (for example, P0301 is a cylinder-1 misfire, the example DPS uses), so you can look up likely causes and get a sense of the repair before visiting a shop;
the I/M readiness status, the same "Ready / Not Ready" monitors the station checks. Look for a reader that shows "I/M readiness" or "emissions readiness."

Some causes DPS lists for OBDII failures: a failed catalytic converter, faulty gas cap, fuel metering out of spec, ignition timing, mis-routed vacuum lines, and faulty PCV or EGR systems (DPS). A loose gas cap is the cheap fix worth ruling out first.

Inexpensive OBD2 code readers

You don't need a professional scanner. A basic reader that shows codes, can clear them, and displays I/M readiness is enough for most drivers. Plug-in Bluetooth adapters that work with a phone app are another low-cost option.

Browse OBD2 code readers with I/M readiness on Amazon
Browse Bluetooth OBD2 adapters on Amazon

Affiliate disclosure: As an Amazon Associate I earn from qualifying purchases. If you buy through these links, the price is the same for you. We don't accept payment from inspection stations or repair shops, and a code reader is never required. Many auto-parts stores and repair shops will also read codes for you.

Step 2: repair, then verify

After the repair, drive normally until the readiness monitors show "Ready," then get tested.
If the repair is expensive and the vehicle still fails, waivers and extensions may apply, but only after a failed test. A Recognized Emissions Repair Facility matters for waivers. See failed-test options.
Transmission trouble codes also turn on the light and fail the test. DPS has specific guidance and says only diagnoses from a Recognized Emissions Repair Facility or dealership count for that type of waiver (DPS).

This page is general information, not mechanical advice. When in doubt, have a qualified technician diagnose the vehicle.

Sources for this page

Last updated: October 2026. Every rule, fee and date on this page comes from the official sources above. If anything here disagrees with them, the official source wins. Report an error.