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ASE School Bus

S4 School Bus — Brakes — practice test

Studying for S4 (School Bus — Brakes)? Overhaul Prep has 170 verified S4 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.

170S4 questions
100%with explanations
9,711questions in total
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Sample S4 questions

Straight from the bank — answers highlighted, with the explanation underneath.

The device that senses reservoir pressure and loads or unloads the air compressor to keep system pressure within a set range is the:

  1. Air dryer purge valve
  2. Governor
  3. Safety relief valve
  4. Quick-release valve
WhyThe governor monitors reservoir pressure and signals the compressor's unloader to stop pumping at cut-out and resume at cut-in, holding pressure in range.

Technician A says the governor controls the compressor's cut-in and cut-out pressures. Technician B says that when the compressor is unloaded, it stops turning. Who is correct?

  1. Technician A only
  2. Technician B only
  3. Both Technicians A and B
  4. Neither Technician
WhyA is correct. When unloaded, the compressor keeps turning with the engine; the unloader simply holds the intake open so it stops pumping air, so B is wrong.

A school bus hydraulic brake pedal feels soft and spongy and travels farther than normal, but fluid level is correct and there are no external leaks. The MOST likely cause is:

  1. Air trapped in the hydraulic system
  2. A seized caliper piston
  3. A worn wheel bearing
  4. A high governor setting
WhyA spongy, low pedal is the hallmark of air in the hydraulic lines, because air compresses where fluid does not. Bleeding the system removes the air and restores a firm pedal.

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