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ASE Medium / Heavy Truck

L2 Electronic Diesel Engine Diagnosis — practice test

Studying for L2 (Electronic Diesel Engine Diagnosis)? Overhaul Prep has 107 verified L2 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.

107L2 questions
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9,711questions in total
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Sample L2 questions

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

A truck sets an active SPN 636 FMI 8 (camshaft position sensor - abnormal frequency/pulse width/period) with the engine running rough. The tech scopes the sensor and sees a clean AC sine wave that grows in amplitude with rpm. What does this signal characteristic indicate about the sensor type?

  1. It is a Hall-effect sensor and the signal is normal
  2. It is a variable-reluctance (magnetic) sensor and the waveform is consistent with a VR sensor
  3. It is a 3-wire pressure sensor being misread
  4. The signal is faulty because a cam sensor should produce a square wave
WhyA rising-amplitude AC sine wave that increases with speed is the signature of a variable-reluctance (magnetic pickup) sensor. Hall-effect sensors produce a fixed-amplitude square (digital) wave regardless of speed.

Technician A says an inactive (previously-active) fault code means the fault condition was present at some point but is not present now. Technician B says a pending code has met enough criteria to store but has not yet illuminated the lamp or matured to active. Who is correct?

  1. Technician A only
  2. Technician B only
  3. Both Technicians A and B
  4. Neither Technician
WhyBoth statements are correct. Inactive/previously-active codes logged a fault that is no longer occurring, while a pending code has been detected but has not yet satisfied all criteria to mature and command a lamp.

An engine cranks but will not start. A relative-compression (starter-current) test shows one cylinder's current draw is noticeably lower than the others, and a cylinder-contribution test is unavailable because it won't start. The MOST likely cause of the uneven starter-current pattern is:

  1. A weak electronic injector on that cylinder
  2. Low mechanical compression (e.g., a burned valve or worn rings) on that cylinder
  3. A faulty crankshaft position sensor
  4. A discharged battery
WhyRelative-compression testing reads starter current, which spikes as each cylinder compresses; a cylinder that draws less current is not building normal compression, pointing to a mechanical (valve/ring/head-gasket) problem. Injector faults do not affect cranking compression current.

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