Michigan SOS mechanic test

Heavy-Duty Engine Repair – Diesel

Heavy-Duty Engine Repair – Diesel is one of the 20 Secretary of State mechanic certification tests. Here's what the test covers, according to the state's published outline.

Topic guide · questions soon

What's on the test

Official topicWeight
Engine components
  • Piston rings
  • General piston knowledge
  • Aftercooler operation
  • Oil temperature
  • Oil distribution
  • Turbo charger operation
  • Valve bridge function
22%
Engine mechanical diagnosis
  • Turbocharger diagnosis
  • Coolant in crankcase
  • Exhaust smoke diagnosis
  • Engine operating temperature
  • Oil pressure diagnosis
  • Engine tear down diagnosis
  • Blow by
  • Connecting rod diagnosis
  • Engine misfire
20%
Fuel systems
  • Types of injection
  • Leaky fuel lines
  • Fuel system diagnosis
  • Fuel filter diagnosis
12%
Skills in measuring
  • Measuring tools
  • Reading Plastigage
  • Reading a micrometer
  • Crankshaft end play
10%
Fundamentals
  • Using a digital multimeter
  • Bolt grades
  • Understanding 4-stroke engines
  • Valve lash adjustment
14%
Electronic controls and after-treatment
  • EGR operation
  • DEF function and maintenance
  • DPF function and maintenance
  • Diesel oxidation catalyst (DOC)
22%

Source: SOS Mechanic Testing Categories Overview (PDF). Test format: most SOS mechanic tests have 55 questions, and a few have 65–100 (SOS FAQ). Passing scores vary by test; your result letter shows the passing score and your score.

Practice questions coming soon

The Heavy-Duty Engine Repair – Diesel practice bank is being written to the official outline below. The All-Mechanic pass will include it when it launches.

Banks available now: Engine Repair · Front End, Suspension & Steering · Brakes & Braking Systems · Electrical Systems · Engine Tune-Up & Performance

Test-day facts

Source: michigan.gov/sos mechanic testing

Heavy-Duty Engine Repair – Diesel test FAQ

How many questions are on the Michigan Heavy-Duty Engine Repair – Diesel test?

The Secretary of State says most mechanic tests have 55 questions and a few have 65 to 100. The test is “quick pass,” so it ends as soon as you reach the minimum passing score.

What topics are on the Heavy-Duty Engine Repair – Diesel test?

The SOS Mechanic Testing Categories Overview lists: Engine components (22%), Engine mechanical diagnosis (20%), Fuel systems (12%), Skills in measuring (10%), Fundamentals (14%), Electronic controls and after-treatment (22%).

How much does the test cost, and where do I take it?

Each mechanic test costs $18 (effective July 1, 2026). Tests are taken on a touch-screen kiosk at any Secretary of State office; pre-register and schedule through SOS Online Services. Approved automotive schools can also test their students.

Are these the real test questions?

No. MI Trade Prep questions are original practice items written to the official topic outline. They are not actual exam questions, and MI Trade Prep is not affiliated with the Michigan Department of State.

Sources: SOS mechanic testing · SOS mechanics page · SOS mechanic FAQ