How to Become an ASE Certified Diesel Mechanic

You may have seen the sign that invites unhappy teenagers to move out, get a job, and pay their own way while they still know everything. Ah, to be 16 again, thinking that you do know everything, life is simple, and soon you will be done with stupid ol’ tests and dumb ol’ school. Now you are in your 20s and reality has set in. You have a job. You pay your own way. The job is leading nowhere and the pay barely gets you started on your own way. You realize you need more skills. Becoming an ASE certified diesel mechanic can be, for all the testing required, an excellent path to a better life.

ASE Certification

The National Institute for Automotive Service Excellence (ASE) provides rigorous certification in every type of auto repair skill out there. The path to the highest level of diesel mechanic certification, the L2 test, is an uphill challenge, because ASE has a key word in its very name: Excellence. Only those with excellent diagnostic skills, good reasoning capability, and deep understanding of the workings of auto and truck engines will earn the certification.

Test Anxiety

Many adults, long out of school, have real nightmares about taking tests in high school. If you were not good at taking tests, you may unconsciously avoid any chance at improving your career or income if you think you will need to take yet another test.

The best way to overcome test anxiety is…to take tests. You take them every day, though you may not realize you do. If you are currently working in an automotive shop, every car that comes in for service is a real-life test, and your job depends on passing the test. Make the right repair and you pass.

Paper and pencil tests do scare people, but you have many resources to learn test-taking strategies. The simple reality is, you must take three tests to reach the L2 certification.

Steps to Certification

The path begins with getting ASE certified in both diesel engines and electrical/electronic systems. Like a take-out menu, you must select one from Column A and one from Column B:

·  A9, Light Vehicle Diesel Engines


·  T2, Medium/Heavy Duty Truck Diesel Engines

·  H2, Transit Bus Diesel Engines

·  S2, School Bus Diesel Engines

·  A6, Light Vehicle Electrical/Electronics


·  T6, Medium/Heavy Duty Truck Electrical

·  H6, Transit Bus Electrical/Electronics

·  S6, School Bus Electrical/Electronics

So those are two tests of about 100 questions, total, and they are challenging. From ASE’s informative booklet, here is a typical question from the T2 test:

A diesel engine is operated under a load. Coolant continually comes out of the radiator overflow and there are bubbles in the radiator. What is the most likely reason?

If you knew the cause was a compression leakage in the cooling system, you may already be able to take and pass this test. If not, you need to get a solid diesel mechanic education and study, study, study.

Big Leagues

After getting not one, but two ASE certifications by taking and passing the two tests, you need three years’ experience working in a shop before you are able to take the Electronic Diesel Engine Diagnostic Specialist Test. You will answer 45 multiple-choice questions in two hours. The test is divided into four areas:

  1. General Inspection and Diagnosis (4 questions, 9 percent)
  2. Electronic Engine Controls Diagnosis (27 questions, 60 percent)
  3. Air Induction and Exhaust Systems Diagnosis (6 questions, 13 percent)
  4. Fuel Systems Diagnosis (8 questions, 18 percent)

Why Bother?

Diesel Mechanic SalaryAn ASE certified diesel mechanic makes good money. The Bureau of Labor Statistics shows that the median annual wage as of May, 2014 for diesel service technicians and mechanics was $43,630. State and local government mechanics made even higher median annual wages: $50,680. Either of these figures is significantly higher than the average of all occupations, $35,540.

Taking the ASE tests is an investment in your own future. But, as we said, some people get test anxiety, or may not even know how to study.

How to Study

An online study tool is, with hundreds of study sets on diesel mechanic and ASE topics. At you can also create your own practice tests and take them as many times as you like.

Another excellent way to study, to improve your chances of passing both the preliminary certification tests and the L2, is by enrolling in a comprehensive diesel repair course. ATI’s Heavy Vehicle Technology with Service Management degree program can be completed in as little as 14 months. Along the way, you could acquire the skills and knowledge needed to begin work in a diesel repair facility. Soon, you’ll be on your way to those ASE tests and the coveted certifications.

Diesel/Heavy Vehicle Mechanic Training

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