What ASE Certification Tests Measure

ASE (Automotive Service Excellence) certification tests are standardized exams that measure a technician's knowledge of vehicle repair and maintenance across specific systems. The tests are created and administered by the National Institute for Automotive Service Excellence, a nonprofit organization that has been running these exams since 1972. Each test focuses on one area — engine repair, transmission, brakes, electrical systems, and so on — and a technician can hold multiple certifications by passing different tests.

For emissions testing specifically, the relevant ASE test is the A9 Light Duty Diesel Engines test or the L1 Advanced Engine Performance test, depending on whether the vehicle runs on diesel or gasoline and what depth of diagnosis the technician needs to demonstrate. The A9 covers diesel engine systems including emissions controls. The L1 covers advanced diagnostics for all fuel types and is the most rigorous emissions-related certification available.

These tests do not measure whether someone can pass a vehicle through an emissions inspection at a testing station. Instead, they measure whether a technician understands how emissions systems work, can diagnose failures, and can repair them correctly. A shop may require ASE certification for technicians who work on emissions problems because the certification shows the technician has met a national standard.

Key Takeaways

  • ASE tests are written exams administered by the National Institute for Automotive Service Excellence and cover specific vehicle systems, including emissions controls.
  • The L1 Advanced Engine Performance test is the primary certification for emissions diagnostics and repair across all vehicle types.
  • You must have hands-on work experience in the field before you can sit for an ASE test — typically two to five years depending on the test.
  • Tests are offered year-round at testing centers, cost between $130 and $180 per test, and results are available within two weeks.
  • ASE certification is not required by law but is widely recognized by employers and customers as proof of technical competence.

Experience Requirements Before You Can Test

ASE does not let someone walk in off the street and take a test. You must have documented hands-on work experience in the field you want to certify in. For most ASE tests, including the L1 emissions test, you need a minimum of two years of full-time work experience as an automotive technician. If you have completed a formal automotive training program at a school or community college, ASE will reduce that requirement to one year of work experience.

The experience must be verifiable — you will need to provide the names and contact information of employers or supervisors who can confirm you worked in that role during those dates. ASE may contact them to verify. If you cannot document the required experience, your test registration will be rejected and your fee will not be refunded.

This requirement exists because the tests assume a baseline of practical knowledge. Someone who has never diagnosed a vehicle cannot meaningfully answer questions about what a failed oxygen sensor reading means or how to use a scan tool to read diagnostic trouble codes.

What the L1 Advanced Engine Performance Test Covers

The L1 test has 50 to 60 multiple-choice questions and covers four main areas: general engine diagnosis, fuel systems, ignition systems, and emissions systems. Within emissions, the test asks about oxygen sensors, catalytic converters, exhaust gas recirculation (EGR) systems, evaporative emissions controls, and secondary air injection systems. You will see questions about reading diagnostic codes, interpreting scan tool data, and identifying which component is most likely causing a specific symptom.

The test assumes you know how to use a multimeter, a scan tool, and a smoke machine. It assumes you understand how a catalytic converter works and what happens when it fails. It assumes you can read a wiring diagram and understand the difference between a hard fault and an intermittent fault. The questions are scenario-based — you might be told that a vehicle has a check engine light and a specific code, then asked which test you would perform first to narrow down the cause.

You cannot bring reference materials, calculators, or notes into the testing room. You have 90 minutes to complete the test. A passing score is typically around 70 percent, though ASE does not publish the exact cutoff because it adjusts slightly based on the difficulty of each test administration.

How to Register and Where Tests Are Held

ASE tests are offered year-round at testing centers across the United States. You register through the ASE website (ase.com) or by calling their registration line. You choose your test, select a testing center near you, and pick a date that has availability. Registration typically closes two business days before the test date. The fee per test is between $130 and $180, depending on whether you register online or by phone and how close the test date is.

Testing centers are usually located at community colleges, vocational schools, or independent testing facilities. When you arrive, you will need to bring a government-issued photo ID and your registration confirmation. You will not be allowed to bring a phone, smartwatch, or any electronic device into the testing room. The test is administered on a computer, and you move through questions at your own pace.

Results are available within two weeks of the test date. ASE sends results by email and also posts them in your online account. If you pass, you receive a certificate and can use the ASE credential in your job title and on business cards. If you do not pass, you can register for the same test again as soon as you want, though most people study for several weeks before retesting.

Preparing for the Test: Study Materials and Practice

ASE publishes official study guides for each test, available through their website and through major book retailers. These guides walk through the content areas covered on the test and include sample questions. Many people also use third-party study materials — online courses, YouTube videos, and practice test apps — though these vary in quality and accuracy.

The most effective preparation involves both reading and hands-on practice. Reading alone will not prepare you for the scenario-based questions because you need to know not just what a component is, but how to diagnose it when it fails. If your job involves emissions work, you are already building this knowledge. If you are studying for the test outside of work, you may need to spend time in a shop or borrow a vehicle to practice with diagnostic tools.

Many employers offer study time or tuition reimbursement for technicians pursuing ASE certification. Some shops have in-house study groups or mentorship programs. If you are studying on your own, budget 40 to 60 hours of preparation time, spread over four to eight weeks, depending on your background.

What Happens After You Pass

Once you pass an ASE test, your certification is valid for five years. During that time, you can use the ASE credential on your resume, business cards, and shop signage. Many shops display the ASE certifications of their technicians in the waiting room or on their website because customers recognize it as a mark of quality.

To keep your certification active after five years, you must retake the test. You do not have to wait until the five years are up — you can retake it at any time. Some technicians retake it every three years to stay current with changes in vehicle technology. Others wait until the certification is about to expire.

ASE also offers a Master Technician credential if you pass eight or more tests across different systems. This is a higher-level recognition that some shops use to identify their most experienced technicians or to may have access to for certain types of work.

Frequently Asked Questions

Do I need ASE certification to work on emissions systems?

No. ASE certification is not required by law in any state. However, many shops require it for technicians who diagnose or repair emissions problems, and some customers specifically request ASE-certified technicians. It is a competitive advantage in the job market, not a legal requirement.

What if I fail the test?

You can retake it as many times as you need. There is no limit on attempts. Most people who fail study for another four to six weeks and pass on the second try. You pay the full test fee each time you register.

Can I take the test online from home?

No. ASE tests must be taken at an authorized testing center in person. You cannot take them remotely. This is to prevent cheating and may support the integrity of the certification.

How long does it take to get my results?

Results are posted within two weeks of your test date, usually within five to seven business days. You will receive an email notification when your results are available, and you can also log into your ASE account to view them.

Is there a difference between ASE certification and a state emissions license?

Yes. ASE certification is a national credential issued by a nonprofit organization and shows technical knowledge. A state emissions license is issued by your state's environmental or motor vehicle agency and shows you are legally permitted to perform emissions testing or repairs in that state. Some states require both; some require only one. Check your state's requirements.