S2 School Bus — Diesel Engines — practice test
Studying for S2 (School Bus — Diesel Engines)? Overhaul Prep has 170 verified S2 questions written to the current task list — in the same formats the real exam uses (direct, Technician A/B, EXCEPT and most-likely-cause). Every answer comes with a written explanation, so you learn why instead of memorising a letter.
Sample S2 questions
Straight from the bank — answers highlighted, with the explanation underneath.
A diesel engine emits heavy black smoke under load. Black exhaust smoke is caused by:
- Excess air relative to the fuel delivered
- Incomplete combustion from too much fuel or too little air
- Coolant entering the combustion chamber
- Engine oil passing the piston rings
Technician A says a turbocharger increases power by forcing more air into the cylinders. Technician B says the turbocharger's compressor wheel and turbine wheel are mounted on a common shaft. Who is correct?
- Technician A only
- Technician B only
- Both Technicians A and B
- Neither Technician
A diesel produces black smoke and lacks power under heavy load, and measured boost pressure is below specification. The MOST likely cause is:
- Worn valve seals
- A restricted air intake or a turbocharger/boost problem
- Coolant in the oil
- A stuck-open thermostat
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