• 50 questions

Diesel NOCTI Test Practice

Unofficial practice for NOCTI Diesel Technology: safety, shop tools, engines, steering, brakes, electrical, drivetrains and preventive maintenance.

Spilled fuel and oil are burning on the shop floor. Which class of fire is a flammable liquid fire?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

Print covers the next 50 questions. Share this set copies a link to the same questions in the same order.

Exam mode: 50 questions, 50 minutes.

More options

Unofficial practice questions, not affiliated with NOCTI. Bank checked October 13, 2026.

Next step Another NOCTI test: Automotive Technician

All 50 questions

Safety 4

  • A shop stocks brake cleaner, coolant and battery acid. Where must the safety data sheets for them be? OSHA, 29 CFR 1910.1200. Written to NOCTI Diesel Technology (4227), Safety
  • A technician blows dust off a part with shop air. To what pressure must compressed air be reduced when it is used for cleaning? OSHA, 29 CFR 1910.242. Written to NOCTI Diesel Technology (4227), Safety
  • A truck tire on a multi-piece wheel is off the vehicle and ready for air. What must the shop furnish for inflating it? OSHA, 29 CFR 1910.177. Written to NOCTI Diesel Technology (4227), Safety
  • Spilled fuel and oil are burning on the shop floor. Which class of fire is a flammable liquid fire? Wikipedia, Fire class, Flammable liquids. Written to NOCTI Diesel Technology (4227), Safety
Show all 50 questions (46 more)

Shop Practices, Tools, and Equipment 6

  • A hydraulic line ends in a JIC fitting. What is the angle of its flare seating surface? Wikipedia, JIC fitting. Written to NOCTI Diesel Technology (4227), Shop Practices, Tools, and Equipment
  • A service manual gives a bolt torque of 100 pound-feet. The only torque wrench on the bench reads in pound-inches. What is the equal setting? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Shop Practices, Tools, and Equipment; the arithmetic was worked twice
  • A slotted nut on a tie rod end is torqued, and then a pin is pushed through the slots and a hole in the stud. What does the pin do? Wikipedia, Castellated nut. Written to NOCTI Diesel Technology (4227), Shop Practices, Tools, and Equipment
  • An inch micrometer shows 0.350 inch on the sleeve, and line 17 on the thimble meets the index line. What is the reading? Wikipedia, Micrometer (device), Customary/Imperial system. Written to NOCTI Diesel Technology (4227), Shop Practices, Tools, and Equipment; the arithmetic was worked twice
  • Which hand tool is a set of thin steel blades of different thicknesses, used to measure the clearance between two parts? Wikipedia, Feeler gauge. Written to NOCTI Diesel Technology (4227), Shop Practices, Tools, and Equipment
  • Which instrument has a clock-like face and a probe, and reads very small distances such as how far a surface is out of true? Wikipedia, Indicator (distance amplifying instrument). Written to NOCTI Diesel Technology (4227), Shop Practices, Tools, and Equipment

Diesel Engines 7

  • A diesel engine has no spark plugs. What sets the fuel burning in the cylinder? Wikipedia, Diesel engine. Written to NOCTI Diesel Technology (4227), Diesel Engines
  • A scan tool is plugged into a truck's diagnostic port. What does a stored diagnostic trouble code tell the technician? Wikipedia, On-board diagnostics. Written to NOCTI Diesel Technology (4227), Diesel Engines
  • A truck's coolant is a mix of water and antifreeze. Compared with plain water, where do its freezing point and boiling point sit? Wikipedia, Antifreeze. Written to NOCTI Diesel Technology (4227), Diesel Engines
  • How many turns does the crankshaft make in one complete cycle of a four-stroke engine? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Chapter 2, Piston Engine Characteristics. Written to NOCTI Diesel Technology (4227), Diesel Engines
  • In the lubricating system, which part moves oil from the oil pan to the moving parts of the engine? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Diesel Engines
  • Some diesel engines have a device in each cylinder that heats up before cranking on a cold morning. What is it? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Diesel Engines
  • What does a turbocharger do to the intake air? Wikipedia, Turbocharger. Written to NOCTI Diesel Technology (4227), Diesel Engines

Suspension and Steering 5

  • A leaf spring gets longer as it flattens under load. Which part lets one end of the spring swing so its length can change? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Suspension and Steering
  • An inspector checks steering wheel free play on a truck with power steering. What does the federal inspection standard say about the engine? 49 CFR Part 396, Appendix A, Minimum Periodic Inspection Standards (ecfr.gov). Written to NOCTI Diesel Technology (4227), Suspension and Steering
  • The front tires of a truck are 1/8 inch closer together at the front than at the rear. What is this alignment setting called? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Chapter 33, paragraph 33-21. Written to NOCTI Diesel Technology (4227), Suspension and Steering
  • On a steering axle, what is caster? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Suspension and Steering
  • What does a tire-pressure monitoring system (TPMS) report to the driver? Wikipedia, Tire-pressure monitoring system. Written to NOCTI Diesel Technology (4227), Suspension and Steering

Brakes 7

  • A hydraulic brake system is flushed on a schedule because DOT 3 fluid takes on water over time. Which property of glycol-ether fluid causes this? Wikipedia, Brake fluid, Boiling point. Written to NOCTI Diesel Technology (4227), Brakes
  • A loaded truck brakes hard on a wet road and the ABS cycles. What is the system preventing? Wikipedia, Anti-lock braking system. Written to NOCTI Diesel Technology (4227), Brakes
  • A tractor has two gladhands for the trailer air lines. In North America, which color marks the service line? Wikipedia, Gladhand connector. Written to NOCTI Diesel Technology (4227), Brakes
  • In a hydraulic drum brake, which part changes hydraulic pressure into the force that pushes the shoes against the drum? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Chapter 34, paragraph 34-26. Written to NOCTI Diesel Technology (4227), Brakes
  • In an air brake supply system, what does the governor do when system pressure reaches its maximum? Wikipedia, Air brake (road vehicle), Supply system. Written to NOCTI Diesel Technology (4227), Brakes
  • On one axle the left service brake chamber is a different size from the right. What does 49 CFR 393.47 require? 49 CFR 393.47 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Brakes
  • What holds the parking brakes of an air-braked truck in the applied position? Wikipedia, Air brake (road vehicle). Written to NOCTI Diesel Technology (4227), Brakes

Electrical and Electronic Systems 7

  • A battery is tested with a hydrometer. What does the hydrometer measure? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Electrical and Electronic Systems
  • A lamp circuit on a 24-volt truck measures 6 ohms from the battery to ground. By Ohm's law, how many amperes does it draw? Wikipedia, Ohm's law. Written to NOCTI Diesel Technology (4227), Electrical and Electronic Systems; the arithmetic was worked twice
  • A marker lamp is wired to the frame on one side. In vehicle wiring, what is this connection called? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Electrical and Electronic Systems
  • A small dash switch controls a set of high-current driving lamps through a relay. What does a relay do? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Electrical and Electronic Systems
  • A wiring diagram shows three lamps wired one after another, positive to negative, on a single path. What is true of this series circuit? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Electrical and Electronic Systems
  • An alternator produces alternating current, but the battery needs direct current. Which part makes the change? Wikipedia, Alternator (automotive), Advantages over dynamos. Written to NOCTI Diesel Technology (4227), Electrical and Electronic Systems
  • Which part of a starter drive transmits cranking effort to the flywheel but spins freely once the engine starts and tries to drive the starter? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Electrical and Electronic Systems

Drivetrains 5

  • A truck rounds a corner and the outer drive wheel must turn faster than the inner one. Which unit allows this while still driving both axle shafts? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Drivetrains
  • As the rear axle moves up and down, the distance from the transmission to the axle changes. Which part lets the propeller shaft change its length? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Drivetrains
  • What does a synchromesh transmission allow? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Appendix, Definition of Terms. Written to NOCTI Diesel Technology (4227), Drivetrains
  • What is an automated manual transmission (AMT)? Wikipedia, Automated manual transmission. Written to NOCTI Diesel Technology (4227), Drivetrains
  • When the driver presses the clutch pedal, which part moves against the inner ends of the release levers so the pressure plate pulls away from the disk? US Army TM 9-8000, Principles of Automotive Vehicles (1985), Chapter 21, Clutches. Written to NOCTI Diesel Technology (4227), Drivetrains

Preventive Maintenance 9

  • A cooling system holds pressure when a tester is pumped up on the filler neck. Why is the coolant kept under pressure in service? Wikipedia, Radiator (engine cooling), Coolant pressure. Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • A drive axle with air drum brakes is inspected. At the shoe center, below what lining thickness may the truck not be operated? 49 CFR 393.47 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • A shop is paid to recharge the cab air conditioning of a truck. What does the EPA require of the technician who services the system? U.S. Environmental Protection Agency, Section 609 Technician Training and Certification Programs. Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • A technician bleeds the air system down to test the low-pressure warning. Under Federal Motor Vehicle Safety Standard No. 121, the warning must be on when service reservoir pressure is below what? 49 CFR 571.121 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • A truck with air suspension is inspected. Until how much pressure is in the braking system must the regulator valve keep air out of the suspension? 49 CFR Part 393 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • During a tire inspection a steer tire is measured in a major tread groove. What is the least tread depth allowed on a front tire of a truck? 49 CFR 393.75 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • How long must a carrier keep a truck's inspection, repair and maintenance records where the truck is housed or maintained? 49 CFR Part 396 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • How often must a commercial motor vehicle pass the federal periodic inspection? 49 CFR Part 396 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Preventive Maintenance
  • Under 49 CFR 396.5, a carrier must ensure that each vehicle is properly lubricated. What else does that section require? 49 CFR Part 396 (ecfr.gov). Written to NOCTI Diesel Technology (4227), Preventive Maintenance

How this list was compiled: Our own questions, written to the competency list of the Job Ready Credential Blueprint for Diesel Technology (code 4227, version 01, copyright 2022) that NOCTI publishes at https://www.nocti.org/wp-content/uploads/Blueprints/JRDieselTech4227.pdf , read 2026-10-13: a written assessment of 179 questions in 3 hours over eight areas (Safety 8%; Shop Practices, Tools, and Equipment 12%; Diesel Engines 13%; Suspension and Steering 11%; Brakes 13%; Electrical and Electronic Systems 14%; Drivetrains 10%; Preventive Maintenance 19%), plus a performance assessment of six jobs. This bank holds 50 in those proportions. The Teacher blueprint for Diesel Technology prints the same eight areas and weights with 179 questions. Every rule and definition was read on 2026-10-13 on the public page named under its question: the Federal Motor Carrier Safety Regulations in 49 CFR Parts 393 and 396 and Federal Motor Vehicle Safety Standard No. 121 on ecfr.gov, OSHA standards in 29 CFR 1910 on osha.gov, the EPA, US Army TM 9-8000, Principles of Automotive Vehicles (1985, the copy at archive.org) and Wikipedia. Every reading and setting in a sum is made up for the drill, and each computed answer is arithmetic that was worked twice. Licence: Questions, choices and explanations are original work of this site. TM 9-8000 is a work of the United States Army approved for public release, and no question or example is copied from it.

How it works

Diesel NOCTI test practice: 50 questions of our own, sorted by the eight areas of the Job Ready Diesel Technology blueprint, code 4227. This page is unofficial and not affiliated with, endorsed by or sponsored by NOCTI.

Read the full guide

Eight areas, in the blueprint's shares

Preventive Maintenance is 19% of the written assessment. Electrical and Electronic Systems is 14%, Diesel Engines and Brakes 13% each, Shop Practices, Tools, and Equipment 12%, Suspension and Steering 11%, Drivetrains 10% and Safety 8%.

One clock for the whole truck

The timed round runs all 50 questions in 50 minutes, the pace of 179 questions in 3 hours. You get a score and no pass or fail.

What stays in the shop

The six performance jobs are done on real parts: a cylinder liner installation, a wheel bearing adjustment with a brake stroke measurement, rocker lever clearance, a coolant system inspection, electrical testing and trouble codes.

  • Inspection answers cite the federal rule, such as 49 CFR 393.75 for tread depth and 393.47 for lining thickness.
  • On an inch micrometer one full turn of the thimble is 0.025 inch, and each thimble line is 0.001 inch.

Questions and answers

How many questions are on the NOCTI Diesel Technology test?

The blueprint lists 179 written questions with an administration time of 3 hours, given in one, two or three sessions. The six performance jobs take another 2 hours and 45 minutes.

What is on the NOCTI Diesel Technology test?

More than the engine. Preventive Maintenance, the largest area, asks for troubleshooting and upkeep of engine systems, transmissions, cooling, brakes, frame and chassis, HVAC, clutches and tire wear patterns. Brakes covers hydraulic and air systems, with ABS.

Does this cover the NOCTI Teacher test for Diesel Technology?

Yes. The Teacher blueprint for Diesel Technology prints the same eight written areas with the same weights and 179 questions in 3 hours, so one practice test serves both. Teacher tests are given at a NOCTI-approved Area Test Center.

Where is the NOCTI Diesel Technology blueprint?

On nocti.org/credentials/blueprints, as a free PDF: the competency list, each area's weight, ten sample questions and a sample job. The ten samples were read so that no question here repeats one.

More tests

Show 8 more

Browse Safety and Trades