ASE A9 Light Vehicle Diesel Engines — Free Course & Practice Test
The complete ASE A9 course, free on YouTube: 64 video lessons built from ASE's published
A9 task list, with a printable workbook for every module. The ASE A9 exam itself is 60 questions (50 scored + 10 unscored) in 75 minutes.
300practice questions with full answer keys in every course workbook
Task-list based — built from ASE's published task list
General diagnosis, cylinder heads and valve trains, engine blocks, lubrication and cooling, air induction and exhaust, and diesel fuel systems — the complete A9.
Prefer to study on paper? Each module has a printable follow-along workbook with worksheets and practice questions
drawn from the same 300-question bank as the video course.
Seven questions from the ASE A9 question bank, spread across the modules. Pick your answer, then open the reveal
to check it and read the explanation.
Sample question 1 (QA-1, Module 1)
A customer reports a diesel truck "loses power on hills and blows black smoke." The FIRST step in diagnosing this concern is to:
Verify the concern on a road test and record exactly when and how the power loss and smoke occur
Replace the fuel filters
Remove the turbocharger for inspection
Clear all diagnostic trouble codes
Show answer
Answer: A. Diagnosis starts by verifying and characterizing the complaint under the customer's conditions; the pattern (load, rpm, temperature) then directs which systems get tested first. Distractors: B replaces parts on a guess before any evidence exists. C is major disassembly with no test results pointing at the turbocharger. D erases stored codes and freeze frame data that may hold the best early clues. Source: Task A1.
Sample question 2 (QA-2, Module 1)
Before testing, a technician records the VIN and identifies the engine model, calibration, and serial numbers PRIMARILY so that:
The parts department can quote a replacement engine
The customer can be billed for diagnostic time
The correct service information, precautions, and bulletins for that exact engine and calibration can be researched
The warranty administrator can deny the claim
Show answer
Answer: C. Service procedures, specifications, and technical service bulletins are engine-model- and calibration-specific; identifying the exact engine first ensures every later step uses the right information. Distractors: A skips diagnosis entirely. B confuses documentation with billing. D misstates the purpose — identification supports correct repair, not claim handling. Source: Task A2.
Sample question 3 (QB-10, Module 2)
Valve stem-to-guide clearance is measured most directly by:
A compression test
Moving the valve off its seat and reading stem wobble with a dial indicator (or measuring guide bore and stem diameters), compared to specification
A vacuum gauge
Listening with a stethoscope
Show answer
Answer: B. Guide clearance is a physical dimension: stem movement in the guide (valve unseated) or direct bore/stem measurement quantifies it, and excess clearance lets the valve cock in the guide, wearing seats and seals. Distractors: A measures cylinder sealing overall, not guide clearance. C shows manifold vacuum behavior, not dimensions. D hears symptoms but cannot size a clearance. Source: Task B4.
Sample question 4 (QC-1, Module 3)
Before reinstalling an oil pan or front cover on a diesel, the sealing surfaces must be:
Coated with grease so the gasket slides into place
Scratched with a file to help the gasket grip
Cleaned of all old gasket material and sealant, checked for straightness and damage, and assembled with the specified gasket/sealant only where the manufacturer directs
Sealed with extra silicone along the entire flange whether specified or not
Show answer
Answer: C. Gaskets seal against clean, flat surfaces; leftover material creates leak paths, bent flanges need straightening or replacement, and excess sealant squeezes into the engine where it can plug oil passages and pickup screens. Distractors: A contaminates the joint and prevents sealant adhesion. B damages the surface it claims to help. D is a common cause of internal sealant debris and leaks at corners. Source: Task C1.
Sample question 5 (QD-2, Module 4)
A diesel's oil pressure reads lower than expected only when hot, and the oil in the crankcase is a lighter viscosity than the manufacturer specifies. The correct first step is to:
Condemn the main bearings
Change to the specified viscosity and grade of diesel oil, then re-verify pressure before judging engine wear
Install a high-volume oil pump
Remove the oil pressure relief valve
Show answer
Answer: B. Pressure is a function of oil viscosity as well as clearances; testing with the wrong oil invents a wear diagnosis. Correct oil first, then any remaining low pressure is meaningful data. Distractors: A assumes the wear the test was supposed to prove. C masks the cause with a bigger pump. D destroys pressure regulation. Source: Task D1.
Sample question 6 (QE-1, Module 5)
Air filter restriction on a diesel is verified by:
Measuring intake restriction with a restriction gauge/manometer at the specified location and comparing it to the manufacturer's limit (a filter that looks dirty may still be in specification, and a clean-looking one may not be)
Looking at the filter's color
Revving the engine and listening
Weighing the filter element
Show answer
Answer: A. Restriction is a pressure measurement; the gauge (or the restriction indicator it is checked against) decides service, because diesels move large air volumes and over-restriction costs power while under-servicing wastes filters. Distractors: B misjudges in both directions. C cannot quantify a pressure drop. D changes with harmless dust loading that may still be within limit. Source: Task E1.
Sample question 7 (QF-1, Module 6)
A diesel loses power and stalls after 30 minutes of driving, then restarts after sitting with the fuel cap removed (a hiss of in-rushing air is heard). The cause is:
A plugged tank vent (or wrong sealed cap), letting vacuum build in the tank until the supply pump can no longer draw fuel
A failed high-pressure pump
Worn injectors
A restricted DPF
Show answer
Answer: A. The restart pattern and the in-rushing air are the confession: the tank became a vacuum bottle. Venting faults starve engines on a timer set by fuel level and consumption. Distractors: B and C fail immediately and consistently, not on a venting timer. D causes backpressure symptoms, not tank vacuum. Source: Task F1.
All 300 questions for ASE A9 — with full answer keys — are in the printable workbooks above, and every one is
worked through in the free video lessons.
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