ASE offers two main certification tracks for new technicians: the A-series (Automobile) and the T-series (Medium/Heavy Truck). The right path depends on the type of vehicles you work on or plan to work on.

Many technicians start in automotive and transition to diesel as they advance in their careers. Others enter directly into heavy-duty diesel through vocational programs or apprenticeships. Both paths lead to valuable credentials.

The A-series covers light vehicles — cars, light trucks, and vans. It consists of eight core exams (A1–A8) plus A9 (Light Vehicle Diesel Engines).

A1 — Engine Repair

A2 — Automatic Transmission/Transaxle

A3 — Manual Drive Train and Axles

A4 — Suspension and Steering

A5 — Brakes

A6 — Electrical/Electronic Systems

A7 — Heating and Air Conditioning

A8 — Engine Performance

A9 — Light Vehicle Diesel Engines

Passing all A-series exams earns the ASE Master Automobile Technician designation. A9 is particularly relevant for technicians who work on diesel pickups (6.7 Powerstroke, L5P Duramax, 6.7 Cummins).

The T-series covers medium and heavy trucks — the primary path for heavy-duty diesel technicians. It consists of eight exams (T1–T8).

T1 — Gasoline Engines

T2 — Diesel Engines

T3 — Drive Train

T4 — Brakes

T5 — Suspension and Steering

T6 — Electrical/Electronic Systems

T7 — Heating, Ventilation, and Air Conditioning

T8 — Preventive Maintenance Inspection

Passing all T-series exams earns the ASE Master Medium/Heavy Truck Technician designation — the highest credential in heavy-duty diesel.

After establishing your foundation with A or T-series certifications, the L-series offers advanced specialty credentials.

L2 — Electronic Diesel Engine Diagnosis Specialist is the most relevant advanced credential for heavy-duty diesel technicians. It tests advanced electronic diagnostic capability including fault code interpretation, scan tool data analysis, and systematic diagnostic reasoning.

L2 is considered one of the most challenging ASE exams. It is best attempted after you have several years of hands-on diagnostic experience.

For A9 (Light Vehicle Diesel) technicians: AI Diesel Tech covers fault codes for diesel pickups including 6.7 Powerstroke, L5P Duramax, and 6.7 Cummins. Use it to build diagnostic experience on the specific platforms you work on.

For T2/T6 (Heavy Truck Diesel/Electrical) technicians: AI Diesel Tech is purpose-built for heavy-duty diesel fault code diagnosis. It covers Cummins, Detroit Diesel, PACCAR, Volvo, and other major engine families.

For L2 (Advanced Electronic Diesel) candidates: AI Diesel Tech reinforces the systematic diagnostic reasoning that L2 tests at an advanced level. Working through complex fault codes builds the pattern recognition that L2 requires.

Entry-level (0–2 years): Focus on A5 (Brakes) and A6 (Electrical) or T4 (Brakes) and T6 (Electrical). These are foundational systems you will encounter immediately.

Mid-career (2–5 years): Add T2 (Diesel Engines) and T8 (PMI). These cover the core of heavy-duty diesel work.

Advanced (5+ years): Pursue the full T-series Master designation, then consider L2 for advanced electronic diagnostic credentialing.