Study guide
1.2 ASE Question Formats, Research Items, and Scoring
ASE A9 Light Vehicle Diesel Engines Exam
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1 Introduction & Exam Overview
1.1 Current Exam Facts 1.2 ASE Question Formats, Research Items, and Scoring 1.3 Independent Prep Strategy by Content Area Weight
2 Diagnostic Strategy, Scan Data, Inspection, and NVH
2.1 Complaint Verification, VIN, Engine ID, and Service Information 2.2 Scan Tool Data, Freeze Frame, DTCs, and Repair Verification 2.3 Leak Inspection and Engine Compartment Wiring 2.4 Engine Noise and Vibration Diagnosis
3 Smoke, Fuel Quality, Driveability, and Starting
3.1 Exhaust Smoke, Odor, Volume, and Crankcase Pressure 3.2 Fuel Quality, Contamination, Consumption, and Driveability Complaints 3.3 In-Bay Cooling and Lubrication Screening 3.4 No-Crank, No-Start, Battery, and Charging Diagnosis
4 Cylinder Head and Valve Train Diagnosis and Repair
4.1 Cylinder Head Inspection, Thickness, Warpage, Cracks, and Passages 4.2 Valves, Guides, Seats, Springs, Retainers, Locks, and Seals 4.3 Injector/Glow Plug Sleeves, Bridges, Head Gasket Thickness, and TTY Installation 4.4 Valve Train, Lash, Overhead Cam, and Timing Drive
5 Engine Block Diagnosis and Repair
5.1 Pans, Covers, Block Inspection, Deck Height, and Cylinder Walls 5.2 In-Block Camshaft, Crankshaft, Select-Fit Bearings, and End Play 5.3 Pistons, Pins, Rings, Protrusion, and Cooling Jets 5.4 Drive Gear Train, Vibration Damper, Flywheel, Flexplate, and Dual-Mass Flywheel
6 Lubrication Systems Diagnosis and Repair
6.1 Oil Pressure, Sensors, Pump, Screens, and Pressure Regulator 6.2 Oil Cooler, Turbo Lubrication, Filters, and Oil Specification
7 Cooling Systems and Accessory Drive
7.1 Drive Belts, Pulleys, Tensioners, and Alignment 7.2 Thermostats, Water Pump, Coolant Type, Flush, and Bleed 7.3 Radiator, Cap, Pressure Test, Fan, Clutch, Controls, and Shroud
8 Air Induction and Turbocharging
8.1 Air Cleaner, Induction Piping, and Restrictions 8.2 Charge Air Cooler, Piping, and Intake Manifold Pressure Tests 8.3 Turbochargers, Wastegates, and Boost Control 8.4 Variable Geometry Turbochargers and Actuators
9 Exhaust Flow, Glow Plugs, DOC, and DPF
9.1 Intake Manifolds, Exhaust Backpressure, Temperature, and Exhaust Hardware 9.2 Glow Plugs and Inlet Air Heaters 9.3 Diesel Oxidation Catalyst, DPF, and Regeneration
10 SCR, EGR, Throttle Valves, and Crankcase Ventilation
10.1 SCR, Diesel Exhaust Fluid, and NOx Control 10.2 EGR Valves, Coolers, Bypass, Sensors, and Wiring 10.3 Diesel Throttle Valves and Crankcase Ventilation
11 Low-Pressure Fuel Supply
11.1 Fuel Tanks, Vents, Caps, Supply/Return Lines, and Fittings 11.2 Transfer Pump, Water Separators, Filters, Heaters, and Coolers 11.3 Air in Fuel, Priming, Bleeding, and Low-Pressure Regulation
12 High-Pressure Common Rail Fuel Systems
12.1 High-Pressure Lines, Fittings, Seals, Transfer Tubes, and Safety 12.2 Common-Rail Pump, Rail, and Pressure Control 12.3 Common-Rail Injectors, Back-Leakage, and Replacement
13 HEUI, PLN-E, and EUI Fuel Systems
13.1 Hydraulic Electronic Unit Injector (HEUI) Systems 13.2 Pump-Line-Nozzle Electronic and Electronic Unit Injector Systems
14 Fuel Electronics, Scan Diagnosis, and Interrelated Systems
14.1 Injector Calibration Codes, Software Updates, and Control-Module Relearn 14.2 Harnesses, Sensors, Actuators, and DMM Voltage-Drop Testing 14.3 Interrelated Systems, Electronic Throttle, and PTO Controls
1.2 ASE Question Formats, Research Items, and Scoring
Key Takeaways Explain This Topic AI
Technician A / Technician B items are two independent true/false judgments; both statements can be correct, one can be correct, or neither can be correct.
EXCEPT items ask for the statement that is not true or does not apply; three choices are valid facts and the scored answer is the misfit.
About 10 unlabeled research items appear on initial A9 only and are mixed with the 50 scored questions, so you cannot skip the unfamiliar ones.
ASE uses criterion-referenced scoring set by ASE and does not publish a single passing percentage.
Score reports break performance out by the six published content areas, which is how you rebuild a study plan after a fail.
Last updated: September 2026
Why format skill is a scored skill
A9 is a diesel knowledge test written in ASE's A-series house style. A large share of items are Technician A / Technician B stems. A smaller share are EXCEPT stems. The rest are direct four-choice questions. A technician who can explain Duramax rail-pressure control in the bay but collapses two statements into one gut feeling will give away items that were never about brand trivia. This section teaches how to work those formats, how research items sit next to scored items, how criterion-referenced scoring works, and how to read a score report . The practice items here are original teaching items. They are not copied from the ASE Automobile Study Guide sample questions or from any live form.
Direct multiple-choice items
A direct item asks one question and offers four choices. Only one choice is the best answer. Read the stem for the system and the symptom before you look down. On A9 a direct item might ask which test comes first on a no-start 6.7-liter Power Stroke, which smoke color matches oil consumption, or which aftertreatment device uses diesel exhaust fluid (DEF) . Cross out choices that belong to the wrong vehicle class—Class 8 tractor-only procedures on a light-vehicle stem—or the wrong ignition type, such as gasoline spark diagnosis on a compression-ignition complaint.
Use a two-pass clock. Answer the items you can reason in under a minute, flag the rest, then return. Seventy-five minutes for about 60 on-screen items is enough if you do not reread a stem four times. If two choices still look plausible, pick the one that matches published diagnostic order: verify the complaint, prove air and low-pressure fuel, then condemn high-pressure parts.
Technician A / Technician B items
A Technician A / Technician B item gives two independent statements. You decide, for each statement, whether it is correct. The four answer choices are almost always:
- Technician A only
- Technician B only
- Both Technician A and Technician B
- Neither Technician A nor Technician B
Evaluate each statement independently. Do not let a confident Technician A drag Technician B along. Do not assume ASE would refuse to write two correct statements— both can be right . Both can also be wrong. The stem is two true/false questions glued together. Your job is to finish those two judgments and then select the choice that matches the pair.
Worked example used only for teaching, not as an official sample: a 2019 Ram 2500 with the 6.7-liter Cummins has a low-power complaint after a charge-air hose was replaced. Technician A says a loose charge-air cooler (CAC) boot can lower boost and reduce power even if the high-pressure fuel system is healthy. Technician B says you should still verify low-pressure fuel supply and air-filter restriction before condemning injectors. Both statements are correct diesel practice, so the matching choice is both technicians. If Technician B had said to skip boost testing and replace the injectors first, only Technician A would be correct.
That bay habit already exists in a good shop. One tech says the diesel particulate filter (DPF) is the cause. Another says the turbocharger is the cause. You test each claim. On the exam, write a mental true or false next to A and next to B, then pick the matching choice. If you cannot decide on one statement, guess on that statement only. Do not throw away the statement you already know.