Heavy Duty Equipment Technician Red Seal Exam: The Complete Guide

The HDET Red Seal exam is one of the broadest trade exams — diesel engines, hydraulics, electrical systems, powertrains, steering, brakes, frames, and undercarriages all in one sitting. If you work specifically on highway trucks and want the US diesel credential, see our guide to the ASE T2 Diesel Engine exam. For difficulty context, see our article on Red Seal exam pass rates.

The Exam Format

[VERIFY] The Red Seal HDET exam (421A) has 125 multiple-choice questions. 4 hours. Pass mark is 70%.

The NOA Breakdown

A — Common Occupational Skills: ~19 questions (15%). Safety, rigging, trade math, blueprints, schematics, diagnostic tools.

B — Engines and Engine Support Systems: ~30 questions (24%). Largest section. Diesel engines, fuel systems (HPCR, EUI, HEUI), air induction/exhaust (turbo, DPF, SCR, DEF, EGR), cooling, lubrication, ECMs.

C — Electrical and Electronic Systems: ~23 questions (18%). Starting/charging, batteries, lighting, ECMs, multiplexing (CAN bus, J1939), diagnostics.

D — Drivetrain: ~24 questions (19%). Clutches, manual/automated transmissions, torque converters, hydrostatic drives, differentials, final drives.

E — Chassis Systems: ~29 questions (23%). Second-largest. Steering (hydraulic, articulated), brakes (air brakes, ABS, retarders), suspension, frames, undercarriages.

Engines (B) and Chassis (E) together account for 47%.

Where Candidates Struggle

Air brakes (governor pressures, static leak test limits, applied stroke criteria). Electrical/CAN bus/multiplexing. Hydrostatic drive diagnosis (charge pressure, case drain flow).

The HDET Red Seal Exam Prep book gives you 1,000 practice questions across 8 full-length tests.

[Get the Heavy Duty Equipment Technician Exam Prep book on Amazon →]

[See the full Heavy Duty Mechanic trade page → /heavy-duty-mechanic/]

Frequently Asked Questions

How many questions?

[VERIFY] 125 multiple-choice. 4 hours. 70% pass mark.

Is it the same as ASE T2?

No. The Red Seal HDET is Canadian and covers the full scope of heavy equipment. ASE T2 is US-specific to diesel engines on medium/heavy trucks. Red Seal is broader; ASE T2 goes deeper on diesel engines specifically.

Are air brakes on the exam?

Yes. One of the most heavily tested sub-topics in Chassis Systems. You need the dual-circuit air brake system, governor operation, relay valves, spring brakes, brake timing, and air brake test procedures.