Diesel Mechanic working under raised cab

In order to rise through the ranks of the diesel mechanic profession, there is a need to acquire certifications that are specific to this discipline. Diesel mechanic certifications serve as evidence that an individual has reached an elevated skill level. These certifications can be used to obtain employment and negotiate higher pay rates. Most employers look highly upon diesel mechanics, who have hold certifications. That often translates into better career opportunities. Earning a certification is the culmination of the diesel mechanic’s educational path that starts off with enrollment in a training program at a post-secondary institution. When that process is followed, it can lead to a blossoming career as a diesel mechanic.


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Penn Foster Career School's online Diesel Mechanics & Heavy Truck Maintenance career diploma program covers basic diesel engine operations, troubleshooting and repair and more. The program helps you to prepare for the National Institute for Automotive Service Excellence (ASE) Certification Medium-Heavy Truck Tests. You can complete this program in as little as seven months, training online — at home or on the go — at a pace that’s right for you.

Diesel Mechanic Certificate of Completion

Students are also taught theory on diesel engines. During the education process, they learn how to use diagnostic scanners, lab scopes, and specialized equipment to test fuel injection, electronic circuits and transmissions. This training prepares students for a long career as a diesel mechanic.

  • Electrical Systems
  • Engine Management Systems
  • Hydraulic Systems
  • Chassis Assemblies
  • Braking Systems
  • Drive Trains

There are many diesel mechanic training programs that are offered by post-secondary schools throughout the United States. These training programs are available at various community colleges, technical institutes and automotive schools. When students complete these curriculums, a certificate of completion is awarded. This is important to know because a certificate is not the same as an industry certification. A certificate provides proof that a diesel mechanic has completed a formal training program. Meanwhile, an industry certification is issued to experienced diesel mechanics, who have displayed a superior knowledge level of this trade. Some of the coursework in a certificate program includes detailed instruction on how to repair and service the following components:

Diesel Mechanic Certification Process

Acquiring an education as a diesel mechanic is the first step on a promising and rewarding career path. Once an educational training program has been completed, then comes the time to start working towards a certification. Work experience is required before a diesel mechanic can sit for an ASE certification exam that is offered by the National Institute for Automotive Service Excellence. Working in the field as a diesel mechanic will help to better understand the theories, procedures and lessons that are taught in a training program. Putting all those elements together will enable diesel mechanics to get a better grasp of their trade.

Certification exams issued by the ASE have a high level of difficulty. It takes both knowledge and practice to earn a passing score. This is one of the main reasons that an ASE certification is held in such high regard. It shows that a diesel mechanic has invested the time, training and practice into becoming an elite member of this profession.

Diesel Mechanic Certification Process

The ASE features a variety of certifications for diesel mechanics. These certifications signify that a mechanic has attained an above-average skill level in a specific area of repair. Each certification test is very extensive and covers all the major areas a seasoned diesel mechanic should know. What follows is a list and description of the diesel engine certifications that are offered by the ASE.

A9 Light Vehicle Diesel Engines - This falls under the Automobile and Light Truck classification. However, it is not needed to become a master technician in that category. This test covers the essentials of repairing diesel engines in automobiles and light trucks.
T2 Medium Heavy Truck Diesel Engines – This is one of three certifications needed to earn master technician status for transit busses. This is a completely different distinction from that of school busses and has its own unique areas of concentration.
H2 Transit Bus Diesel Engines –This is one of three certifications needed to earn master technician status for transit busses. This is a completely different distinction from that of school busses and has its own unique areas of concentration.
S2 School Bus Diesel Engines – This examination consists of 55 questions and aims to gauge a mechanic’s knowledge on all the subsystems of a school bus. This test was actually formed to fulfill a request made by the National Association for Pupil Transportation.
L2 Electronic Diesel Engine Diagnosis Specialist – This certification requires that a diesel mechanic passes one of the previously-mentioned certification tests (A9, T2, H2) as well as one of the ASE Electrical Systems certification tests (A6, H6, S6 or T6). This certification test is more complex and signifies a higher level of skill.

Brakes All of those certifications differ in subject matter, but all focus on the same engine components. Here is a look at some of the areas covered in these certification tests:

  • General Diagnosis and Repair
  • Valve Train and Cylinder Head Diagnosis
  • Engine Block Repair and Diagnosis
  • Lubrication and Cooling Systems
  • Air Induction and Exhaust Systems
  • Starting Systems
  • Fuel System Diagnosis

Diesel Mechanic Electrical Certifications

Electrical certifications for diesel mechanics are available in the same categories that feature diesel engine certifications. These certifications are important because it shows a superior knowledge of the electrical systems that are used in diesel engines. Those Electrical/Electronic Systems certifications are as follows:

A6   Auto and Light Truck
H6   Transit Bus
S6   School Bus
T6   Medium Heavy Truck

There are a number of electrical components within all types of engines, which is why it is extremely important for mechanics to be well-versed in this area. When being tested in these classifications, mechanics will need to demonstrate a high level of knowledge when it comes to each of the following topics:

  • Electronic System
  • Battery System
  • Starting System
  • Charging System
  • Lighting Systems
  • Related Vehicle Systems

Diesel Mechanic Certification Requirements

There is a work experience requirement which is shortened when a mechanic has graduated from an accredited diesel mechanic post-secondary training program. Those who have no formal education usually have to acquire an additional year or two of work experience before being cleared to take an ASE examination. Each certification test has its own set of requirements, meaning that there is a specific process that mechanics will have to follow in order to become eligible.

That process included filling out work experience forms which are sent to the ASE. Those forms will need to be verified before a mechanic is cleared to sit for a certification exam. Diesel mechanics should have a command of the specific areas they will be tested on, as these exams are considered to be rigorous in nature.

Certifications are valid for five years. At that time, diesel mechanics are asked to take a recertification exam, which consists of about half as many questions as the original certification exam. There is also a short grace period in the event that a certification lapses.

Diesel Mechanic Certification Testing

There is a very precise process when it comes to taking an ACE certification test. These tests are only administered on certain dates and at certain locations. Those looking to take the exams must first qualify by meeting all the necessary requirements. A mechanic’s identity will also be checked through the use of a valid government ID. An admission ticket is required for testing.

The tests consist of written questions and do not include any practical portions in which mechanics will be asked to perform some kind of engine repair or service. Questions are prepared by a panel of industry experts. There is an in-depth format by which these questions are selected, and they are also subject to change each year. A variety of study guides are available to help mechanics prepare for the examination. Time limits are set for each test and all conclude with a customer satisfaction survey.

Benefits of Earning a Diesel Mechanic Certification

As previously mentioned, there is a wealth of benefits that come with earning an ASE diesel mechanic certification. Mechanics looking to earn the status of master technician will typically need the diesel engine certification in their particular area of expertise. The accumulation of master status generally takes quite a few years because of all that is involved. However, a diesel mechanic certification can strengthen the overall prominence of a shop and an individual.

Customers tend to feel more comfortable bringing their vehicles and equipment to a repair shop or service center that features ASE certified mechanics. Customers and businesses benefit from mechanics holding one or multiple ASE certifications. It is a claim that is used a great deal in the repair industry. Certifications can also bring diesel mechanics the following benefits.

  • Better job opportunities
  • Higher pay rates
  • Personal satisfaction
  • Validation of overall knowledge
  • Career advancement

More benefits for diesel mechanics can also mean more benefits for their families. An ASE certification is a way of moving a mechanic’s career forward and opening up the door to a wealth of new possibilities. A certification is one of the most valuable assets a diesel mechanic can possess.