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A diesel technician certification is a professional qualification that demonstrates expertise in repairing and maintaining a specific aspect of a diesel-powered vehicle.
What certifications you need to be a diesel technician varies by the state you work in and the company you work for – some jobs don’t require any certifications at all. However, earning a diesel tech certification can open doors to career advancement and higher earning potential.
6 common diesel technician certifications
The National Institute for Automotive Service Excellence (ASE) offers several professional certification tests for medium- and heavy-truck technicians. The tests include the following areas:
1. Brakes.
This certification focuses on a diesel technician’s ability to inspect, clean, repair and/or replace various components in the brake system, such as the:
- Air brakes.
- Hydraulic brakes.
- Air and hydraulic antilock brake systems.
- Electronic stability control systems.
2. Diesel engines.
This certification covers the diagnosis and repair of diesel engines, including its:
- Cylinder head and valve train.
- Lubrication and cooling systems.
- Air induction and exhaust systems.
- Engine block.
- Fuel system.
- Engine brakes.
3. Electrical system.
This certification emphasizes a diesel technician’s knowledge of diagnosing and repairing electrical and electronic systems, such as the:
- Battery and starting system.
- Charging system.
- Lighting systems.
- Related vehicle systems.
4. Heating, ventilation and air conditioning (HVAC).
This certification shows a diesel technician knows how to diagnose, service and repair a tractor’s HVAC system, including its:
- A/C system and component.
- Heating and engine cooling systems.
- Operating systems and related controls.
5. Preventative maintenance.
This certification highlights a diesel technician’s overall technical skills in diagnosing, repairing and maintaining different components in a semi-truck, such as the:
- Engine systems.
- Cab and hood.
- Electrical and electronics systems.
- Frame and chassis.
- Brakes.
- Drivetrain.
- Steering, tires and wheels.
- Suspension, frame and 5th wheel.
- Road and operational test.
6. Suspension and steering.
This certification showcases a diesel technician’s skills in diagnosing and repairing a semi-truck's suspension and steering systems, which includes the:
- Suspension, frame and 5th wheel.
- Wheel alignment.
- Wheels, tires and hub.
Requirements to earn a diesel technician certification
According to the ASE’s work experience requirements, you need a certain amount of hands-on work experience to earn an ASE certificate. You can take many of the ASE tests beforehand, but you will not receive the actual certificate until you fulfill the experience requirement.
Then, once you pass at least one test, you will earn the ASE Medium/Heavy Truck Technician certification in whatever area you tested in. Technicians must retake the test every five years to maintain the certification.
