Diesel & Heavy Duty
Duramax, Powerstroke, Cummins, plus semi trucks.
Diesel & Heavy Duty covers diesel-powered light-duty trucks (Duramax, Powerstroke, Cummins) and Class 7-8 heavy-duty operations. Premium-value certification. Everything below is free, no login, no paywall. Work through the skill areas, drill them in Study Mode, and when you're ready, prove it with the certification exam.
Your readiness to certify
Drill all 60 concepts in Study Mode. Mark each one "Got it" once you know it cold. When every concept is cleared, you're ready for the DSL exam.
What you'll be able to do
- Diesel fuel systems: high-pressure common rail, HEUI, mechanical injection
- Turbocharger diagnosis and service (VGT, twin-turbo)
- DPF (diesel particulate filter) service and regeneration
- EGR system diagnosis and service
- DEF (diesel exhaust fluid) system diagnosis
- Fuel injector testing (electronic and mechanical)
- Boost leak testing methodology
- Class 7-8 introductions: air brake, PTO, heavy-duty electrical
Skill areas
21 lessons, each one short enough to finish in a break. Every lesson teaches the system from the ground up, ends with a call to work, and tracks which concepts you have cleared.
Fundamentals
Everything else in diesel work builds on one idea: these engines light their fuel with heat from compression, not a spark.
Fuel
Diesel fuel is not one commodity — sulfur content, cetane rating, and tax status all matter in the shop.
Injection Systems
The injection system is the heart of a diesel — it decides when fuel arrives, how much, and how finely atomized.
Turbocharger
Nearly every modern diesel is turbocharged, and most heavy-duty applications use variable-geometry turbos.
Emissions
Aftertreatment — DPF, SCR, EGR — is where most modern diesel shop hours go.
Powerstroke
Ford Powerstroke engines dominate a big slice of the light-duty diesel market, and each generation has a well-documented personality.
Duramax
GM's Duramax line has been strong overall, but two failure stories define its shop history: LB7 injectors and CP4 pump catastrophes.
Cummins
The Cummins B-series is beloved for durability, but 'bulletproof' is marketing — each generation has a weak link.
Cold Start
A diesel needs hot compressed air to fire, and cold weather steals exactly that heat.
Injector
Injectors meter fuel with micron-level precision, and when one misbehaves the engine tells you.
Water in Fuel
Water is the natural enemy of a diesel fuel system.
Filters
Filters are where cheap maintenance prevents expensive failure on a diesel.
Oil
Diesel oil is engineered around the emissions system as much as the engine, and diesels have a unique problem gas engines rarely see.
Air System
A diesel makes power in proportion to the air you can stuff into it, so the charge-air side — turbo plumbing, intercooler, EGR.
Diagnostics
Diesel diagnosis rewards discipline: the engine broadcasts its problems through smoke color, start behavior.
Heavy Duty
Class 8 trucks are a different world from pickups.
Injection
Beyond the injectors themselves, the fuel delivery chain — rail sensors, lift pumps, check valves — generates its own family of faults.
Cold Weather
Diesel fuel itself changes character in the cold.
Regulation
California regulates diesel harder than anywhere else in the country, and CARB rules follow the truck, not just the owner's address.
Safety
Diesel fuel systems combine skin-penetrating pressures with surgical-grade tolerances.
Documentation
Paperwork isn't glamorous, but on diesel work it carries legal weight.
Studied the material? Get DSL certified.
The Diesel & Heavy Duty exam turns what you just learned into a verifiable credential drivers and shops can look up. 75 questions · 90 minutes · 78% to pass · Free.
Studying on MechanicRank is free forever. There's no obligation to take the exam.
The work these lessons teach.
Real jobs from Supercanic trucks — the systems above, out in the field.
Standards and further reading
Primary sources behind this page. Federal safety, emissions and consumer-protection references, worth reading before you authorize any repair.
- ASE certification The national standard for automotive technician testing and certification.
- EPA vehicle & engine certification Emissions standards that govern what may be replaced or modified.
- OSHA motor vehicle safety Workplace safety standards for lifting, chemicals and shop equipment.
- California Bureau of Automotive Repair Licensing, consumer complaints and shop regulation in California.