The ASE A9 Light Vehicle Diesel Engines test has 50 scored questions in six content areas, plus 10 unscored questions, and you get 75 minutes for all 60. It is the diesel engine test in ASE's Automobile/Light Truck series. The fuel system is the biggest area at 13 questions (26.0%), then air induction and exhaust at 12 (24.0%), so those two areas make up 25 of the 50, exactly half. General diagnosis has 9 questions (18.0%), lubrication and cooling has 6 (12.0%), and the cylinder head and valve train and the engine block have 5 each (10.0%). Every question ties to one or more tasks in ASE's task list. Questions are four-option multiple choice, including symptom-to-cause, Technician A / Technician B and EXCEPT items. A pass plus documented work experience certifies you for 5 years. A9 is not one of the eight tests for Master Automobile Technician.
01The test specification
The ASE test specification for ASE A9 Light Vehicle Diesel Engines splits the 50 scored questions across six content areas. ASE adds 10 unscored questions for research, and you have 75 minutes for all of them. Each area links to five free questions.
| Area | Content area | Scored questions |
|---|---|---|
| A | General Diagnosis | 9 (18%) |
| B | Cylinder Head and Valve Train Diagnosis and Repair | 5 (10%) |
| C | Engine Block Diagnosis and Repair | 5 (10%) |
| D | Lubrication and Cooling Systems Diagnosis and Repair | 6 (12%) |
| E | Air Induction and Exhaust Systems Diagnosis and Repair | 12 (24%) |
| F | Fuel System Diagnosis and Repair | 13 (26%) |
| Total | 50 |
02What is the ASE A9 Light Vehicle Diesel Engines test?
A9 is the diesel engine test in ASE's Automobile/Light Truck series, the same series as A1 to A8. Its task list follows a light vehicle diesel from the first complaint to the finished repair: diagnosis, the cylinder head and valve train, the block and rotating parts, lubrication and cooling, air induction and exhaust (turbochargers, EGR and aftertreatment included), and the fuel system with its electronic controls.
It has 50 scored questions and 10 unscored ones, 60 in all, and you get 75 minutes. Every question is multiple choice with four options, (A) to (D). ASE puts 10 unscored questions on every certification test to gather statistics for future tests, and you cannot tell which ones they are, so answer every question as if it counts.
Passing is one half of certification. ASE also asks you to document relevant work experience, and its study guide says suitable vocational training may count toward it; the details are at workexp.ase.com. The study guide does not publish a passing score. Once certified, you hold the certification for 5 years.
ASE's Automobile study guide marks A1 to A8 as the tests required for recognition as a Master Automobile Technician. A9 is in the same series but is not on that list, so it stands on its own as a certification. The full picture is in how Master Technician status works.
A9 or T2?
ASE's other diesel engine test, T2 Diesel Engines, is in the Medium/Heavy Truck series for Class 4 through Class 8 trucks. T2 is longer, 55 scored questions in 90 minutes, and has eight content areas: six on the same subjects as A9's, plus Starting and Charging System Diagnosis and Repair (4 questions) and Engine Brakes (3 questions). A9 gives air induction and exhaust 12 questions where T2 gives it 6, and the fuel system 13 where T2 gives it 16. A9 has no starting and charging area, though two of its general diagnosis tasks cover engine problems traced to the battery or the charging system. See the T2 Diesel Engines study guide for that test.
03What does each content area cover?
Area A: General Diagnosis (9 questions)
Eighteen tasks, the longest list on A9. It opens with the groundwork: confirm the complaint on a road test or a dyno, hear what the customer expects, check the service history, and use the VIN and the engine's model, serial and calibration numbers to find the right service information and bulletins. A scan tool check and a walkaround look for parts that are damaged, missing, modified or tampered with. You read and record codes, freeze frame and live data, and after the repair you clear the codes and prove the fix. Inspections cover leaks, the engine harness and its connectors, noise, vibration, and the smoke color, volume and smell at the tailpipe.
The rest is symptom work and system checks: the fuel's quality, contamination and consumption; a crankcase pressure test; surging, rough running, misfire, low power, slow response and shutdowns; and engines that will not crank, crank without starting, start hard, or start and then quit. You check the coolant (freeze protection, level, temperature, pressure, flow and fan) and the oil (level, contamination, pressure, temperature and consumption), with a sample for oil analysis when needed. The last two tasks are engine faults traced to the battery, its connections or a key-off drain, and to a charging system that overcharges, undercharges or does not charge.
Area B: Cylinder Head and Valve Train Diagnosis and Repair (5 questions)
Eleven tasks. You strip and clean the head, check its threads, studs and bolts, measure its thickness, and check the mating surfaces for flatness, warpage and finish, plus cracks, passages and plugs. Valve parts include rotators along with guides, seats, springs, retainers, locks and seals. Two diesel jobs stand out: injector and glow plug sleeves and their seals, pressure tested where that applies, with injector tip, nozzle or prechamber protrusion measured when the maker gives a figure; and valve bridges, also called crossheads. You also choose the head gasket thickness and install the head to the maker's procedure. The list ends with pushrods and rockers, cam followers and lash adjusters, valve clearance, the overhead camshaft with its bearings and endplay, and timing the gear, chain or belt drive.
Area C: Engine Block Diagnosis and Repair (5 questions)
Fifteen tasks for 5 questions, three tasks for every question. It starts outside the block (pans, covers, crankcase ventilation, gaskets, seals and wear rings), then the block itself: cracks, mating surfaces, deck height, passages, plugs, threads and dowels. Inside, you measure the cylinder walls; service the in-block camshaft, its bearings and followers; check the crankshaft journals; pick select-fit pistons and bearings; check main bearing clearance and crankshaft endplay; and set up the timing drive.
Pistons and rods follow: pins and retainers, piston-to-wall clearance, ring end gap and groove fit, piston height, liner height where the engine has liners, rod bearing clearance and the piston cooling jets. One task asks you to read piston and bearing wear for signs of a bent rod, a misaligned crankshaft or a bad bore. The list closes with the vibration damper and the flywheel or flexplate, dual-mass flywheels and the ring gear included.
Area D: Lubrication and Cooling Systems Diagnosis and Repair (6 questions)
Thirteen tasks split between oil and coolant. Oil: confirm pressure and temperature and test their sensors and gauge; the oil pump, its drive and screens; the regulator, filter bypass and anti-drainback valves; the oil cooler; the turbocharger's oil supply and cooling; and an oil and filter change with the type, viscosity and rating the maker specifies. Belts, pulleys and tensioners sit between the two. Coolant: temperature and level sensors, thermostats and bypasses, flushing and refilling with the right coolant and bleeding out the air, the water pump, pressure testing the radiator, cap and system, and the fan, fan clutch, controls and shroud.
Area E: Air Induction and Exhaust Systems Diagnosis and Repair (12 questions)
Eleven tasks for 12 questions, the only A9 area with more questions than tasks. Intake: the air cleaner and piping, intake manifold pressure tests, the charge air cooler, intake manifolds (variable ones included) and their sensors, and the throttle or airflow control valve. Turbochargers, variable geometry (VGT) units included, with their actuators, wastegate and controls. Exhaust: back pressure and temperature tests, manifolds, pipes and mufflers. Cold starting: the intake air heater and the glow plugs.
Three tasks carry the emissions content. Aftertreatment names the diesel oxidation catalyst (DOC), the SCR system and its diesel exhaust fluid (DEF), and the diesel particulate filter (DPF), and asks you to confirm that regeneration works. The EGR task runs from the valve and cooler to the cooler bypass, sensors and wiring. The last covers crankcase ventilation parts.
Area F: Fuel System Diagnosis and Repair (13 questions)
Fifteen tasks. The low-pressure side comes first: tanks, vents, caps and the supply and return lines; the transfer pump, strainers, filters, fuel/water separators, heaters, coolers and ECM cooling plates; checking for air, priming and bleeding, and the primer pump; and the low-pressure regulator and its switches. The high-pressure side starts with injection lines and transfer tubes, then on-engine tests of four injection systems the task list names one by one: high-pressure common rail, hydraulic electronic unit injectors (HEUI), pump-line-nozzle (PLN-E) and electronic unit injectors (EUI), each with its electronic controls.
The rest is electronic: throttle and PTO controls; connector terminals, pins and harnesses; using a scan tool to check and update software calibrations and injector calibration codes and to run module relearns; testing sensors, actuators, control modules and circuits; and taking voltage, voltage drop, current and resistance readings with a multimeter. The final task is an engine problem that starts in some other system, with examples such as cruise control, anti-theft, transmission controls, aftertreatment, stability control and aftermarket accessories.
04What kind of questions are on it?
The A9 section of ASE's Automobile study guide has seven sample questions, and between them they use four formats. Each is multiple choice with four options.
Symptom or code to cause. The question describes a complaint or a trouble code and asks which option could cause it. Decide which system the symptom points to before you read the options, then choose the one that explains the whole complaint, not just part of it.
Technician A / Technician B. Two technicians each make a statement, and you choose A only, B only, both or neither. Judge each statement on its own before you look at the answer grid. See how to answer Technician A / B questions.
Illustration. One sample is built around a drawing with a point marked on it, so expect to read a labeled picture on screen and connect it to a service procedure.
EXCEPT. ASE flags these with a line warning you that the question contains the word EXCEPT. Three options could cause the problem and you are looking for the one that could not. The study guide says questions with special instructions carry the same instructions on the test itself.
None of the A9 samples compares a reading with a specification, but many tasks involve measuring: head thickness, protrusion, clearances, endplay, pressures and electrical readings. Know what each measurement checks and what an out-of-spec result points to.
05Where should your study time go?
Areas F and E together are 25 of the 50 scored questions (50.0%): the fuel system has 13 (26.0%) and air induction and exhaust has 12 (24.0%). Add general diagnosis, 9 questions (18.0%), and those three areas are 34 of 50 (68.0%). The three mechanical areas, B, C and D, share the other 16 (32.0%): 5, 5 and 6.
Start with area F and give each of the four injection systems its own session (common rail, HEUI, pump-line-nozzle and EUI), then the electronic tasks: scan tool work, calibrations and injector codes, sensors and circuits, and meter readings. Area E comes next. Its 11 tasks carry 12 questions, so give aftertreatment, EGR, turbochargers and VGT, the charge air cooler and the cold-start aids real time each. Area A's checks of fuel, smoke, crankcase pressure, coolant and oil lead into the same systems, so study them alongside areas D, E and F.
Areas B and C have 26 tasks between them for 10 questions (20.0%). Cover their measurements for breadth, especially the diesel items (injector and glow plug sleeves, protrusion, crossheads, liners, piston cooling jets), without memorizing every figure. If you have studied for T2, much of the engine content overlaps, but A9 puts twice as many questions on air induction and exhaust.
Use the task list as a checklist and mark each task you could explain to someone else. ASE says every question represents one or more tasks, though some tasks may not appear on the version of the test you get. Pace: 60 questions in 75 minutes is about 1 minute 15 seconds each.
06Registering, retesting and recertifying
You register and pay through ase.com. ASE charges a $34 registration fee per order plus $62 for each test, so A9 on its own comes to $96, and each extra test in the same order adds $62. Fees and dates can change, so check ase.com before you book. The full breakdown is in ASE test fees and registration.
The test is delivered on screen, and ASE offers a demo of its testing platform at ase.com/free-test-drive. As an Automobile series test, A9 has the Leer en español button, which shows each question and its options side by side in Spanish and English with no separate registration, and ASE's Spanish/English pop-up glossary is available during every test. More on the format: how ASE tests work.
If you do not pass, ASE makes you wait 30 days before you can take the test again. Put that month into areas F and E first, since they are half the scored questions.
After you pass, the certification runs for 5 years. To renew it you take the A9 recertification test, 25 questions in 30 minutes. You are eligible for it only after passing the full A9 certification test once.
07Questions people ask
- How many questions are on the ASE A9 Light Vehicle Diesel Engines test?
- 60 questions in 75 minutes: 50 scored and 10 unscored. ASE uses the 10 unscored questions to gather statistics for future tests, and you cannot tell which ones they are, so answer all 60. That is about 1 minute 15 seconds per question.
- What is the biggest content area on ASE A9?
- Fuel System Diagnosis and Repair, with 13 of the 50 scored questions (26.0%). Air Induction and Exhaust Systems Diagnosis and Repair is next with 12 (24.0%). Together they are 25 of the 50 scored questions, exactly half the test.
- Does ASE A9 count toward Master Automobile Technician?
- No. ASE's Automobile study guide lists the eight tests A1 to A8 as required for recognition as a Master Automobile Technician. A9 Light Vehicle Diesel Engines is in the same series but is not on that list, so it is a separate certification.
- How is ASE A9 different from ASE T2 Diesel Engines?
- A9 is in the Automobile/Light Truck series: 50 scored questions in 75 minutes across six content areas. T2 is in the Medium/Heavy Truck series for Class 4 through Class 8 trucks: 55 scored questions in 90 minutes across eight areas, adding starting and charging (4 questions) and engine brakes (3). A9 also puts 12 questions on air induction and exhaust, against 6 on T2.
- How long is the ASE A9 recertification test?
- The A9 recertification test has 25 questions in 30 minutes, against 60 questions in 75 minutes for the A9 certification test. You can take it only after passing the full A9 certification test once. Certification lasts 5 years.
- Is ToolboxPrep affiliated with ASE?
- ToolboxPrep is an independent study site, not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original, written from ASE’s published test specifications and task lists and other public sources. They are not actual ASE test questions and not recalled or “brain dump” questions. ASE is a trademark of its owner, and we never use the ASE logo. Standards and service information are cited, not reproduced.
08Sources
- ASE Automobile Study Guide (Tests A1 to A9), 2026: the A9 test specification, question counts, testing time, the 10 unscored questions, the recertification test length, the task list this page paraphrases, the sample-question formats, the Master Automobile Technician test list, the work experience requirement and the Spanish-language aids
- ASE (ase.com): the $34 registration fee per order, the $62 fee per test, the 5-year certification period and the 30-day retest wait
The content areas and question counts were checked against ASE's published study guide on October 22, 2026, and the task descriptions paraphrase its task list. ASE's study guide is the final word. If you find one of ours out of date, tell us.
Related: free practice questions · ten free A9 questions · How ASE tests work · ASE Master Technician
09Practice for this test
ToolboxPrep A9 practice tests are weighted to the specification above, area by area, and every answer is explained, all four options. You can try five sample questions with no account.
Ten free questions per test, no account: free practice questions. How our questions are written and checked: how our questions are made.
ToolboxPrep is an independent study site, not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original, written from ASE’s published test specifications and task lists and other public sources. They are not actual ASE test questions and not recalled or “brain dump” questions. ASE is a trademark of its owner, and we never use the ASE logo. Standards and service information are cited, not reproduced.