Examination Practice Questions And

Illinois Heavy Truck Technician Certification Examination Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary function of a diesel engine turbocharger?
• Reduce fuel consumption
• Increase air intake pressure
• Cool engine coolant
• Lower exhaust emissions

Rationale: A turbocharger compresses the intake air, allowing more

oxygen into the combustion chamber for increased engine power.

• Which type of braking system is most commonly used on heavy

trucks?

• Hydraulic
• Air 1 / 4

• Electric
• Mechanical

Rationale: Air brakes are standard in heavy trucks due to reliability

and fail-safe design.

• What does the acronym ECM stand for in truck diagnostics?
• Engine Control Module
• Electronic Control Module
• Electrical Circuit Monitor
• Engine Circuit Monitor

Rationale: The ECM controls engine functions and monitors sensors

to optimize performance.

• Which component of the cooling system maintains constant pressure?
• Radiator fan
• Water pump
• Radiator cap
• Thermostat

Rationale: The radiator cap regulates system pressure, raising the

boiling point of coolant.

5. When inspecting a truck’s suspension, worn bushings primarily cause:

• Tire wear
• Excessive play or noise
• Brake fade
• Steering misalignment 2 / 4

Rationale: Worn suspension bushings lead to looseness and clunking

noises.

• What is the primary purpose of engine oil?
• Fuel efficiency
• Lubrication
• Cooling
• Air compression

Rationale: Engine oil reduces friction between moving parts,

preventing wear.

• What is the function of a diesel fuel injector?
• Store fuel
• Filter fuel
• Atomize and deliver fuel to the combustion chamber
• Increase fuel pressure

Rationale: Injectors spray fuel in a fine mist to ensure efficient

combustion.

• Which diagnostic tool is used to read truck ECM fault codes?
• Voltmeter
• Ohmmeter
• Tachometer
• Scan tool

Rationale: A scan tool connects to the ECM to retrieve trouble codes

and monitor sensors. 3 / 4

• What is the purpose of the pushrod in an air brake system?
• Release air from the tank
• Transmit force from the brake chamber to the slack adjuster
• Compress the air
• Apply parking brake

Rationale: The pushrod moves when air pressure enters the brake

chamber to activate braking.

• Which of the following is a common symptom of a failing

turbocharger?

• Engine overheating
• Loss of power
• Excessive fuel economy
• Low oil pressure

Rationale: A failing turbo cannot properly compress air, reducing

engine power.

• In a 12-volt truck electrical system, what is the typical color of

the ground wire?

• Red
• Yellow
• Black
• Blue

Rationale: Black wires are commonly used for ground in vehicle

electrical systems.

• / 4