Technician Practice Exam Questions And

ASE Master Medium-Heavy Truck Technician Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• A diesel engine is smoking black under heavy load. What is the most

likely cause?

a) Low oil level

b) Excess fuel

c) Faulty glow plugs

d) Low coolant level

Rationale: Black smoke indicates incomplete combustion, usually

caused by excess fuel or insufficient air.

• Which type of fuel injector is commonly used in modern heavy-duty

diesel engines?

a) Mechanical injector 1 / 4

b) Carbureted injector

c) Common rail electronic injector

d) Piezoelectric spark injector

Rationale: Most modern diesels use common rail systems with

electronically controlled injectors for precise fuel delivery.

• A truck equipped with an electronic engine control has a MIL

(Malfunction Indicator Lamp) illuminated. What should be the first step?

a) Replace the ECU

b) Retrieve diagnostic trouble codes (DTCs)

c) Replace the sensors

d) Check oil level

Rationale: Diagnosing with DTCs is the correct first step to identify

the source of the problem.

• During a pre-trip inspection, a technician notices oil on the engine

block. What is the safest first action?

a) Ignore it

b) Replace the engine

c) Identify the source of the leak

d) Clean the oil and continue

Rationale: Identifying the source of a leak prevents further damage

and safety hazards. 2 / 4

• A heavy-duty truck engine overheats only under heavy load. What is

the most probable cause?

a) Low engine oil

b) Low coolant

c) Restricted radiator airflow

d) Faulty fuel pump

Rationale: Restricted airflow can cause overheating under load when

heat generation is highest.

• Which tool is used to measure cylinder compression in a diesel

engine?

a) Torque wrench

b) Caliper

c) Compression gauge

d) Manometer

Rationale: Compression gauges measure cylinder pressure to assess

engine health.

• What is the purpose of an EGR (Exhaust Gas Recirculation) valve?

a) Reduce engine noise

b) Increase fuel efficiency

c) Reduce NOx emissions

d) Improve turbo response

Rationale: EGR recirculates exhaust gases to lower combustion

temperatures, reducing NOx emissions. 3 / 4

• What is the first step in diagnosing a no-start condition on a diesel

engine?

a) Replace the starter

b) Check for fuel, air, and compression

c) Check coolant temperature sensor

d) Check brake switch

Rationale: Diesel engines require fuel, air, and compression to start;

verifying these systems is the first diagnostic step.

• Which of the following describes a dual-clutch transmission?

a) Single clutch, manual shifting

b) Torque converter only

c) Two clutches that engage alternate gears

d) Continuously variable

Rationale: Dual-clutch transmissions use two separate clutches to

pre-select the next gear for faster shifts.

• When inspecting a driveshaft, which sign indicates potential

failure?

a) Clean universal joints

b) Correct length

c) Excessive play in U-joints

d) Balanced weight

Rationale: Excessive play in universal joints can cause vibration,

noise, and failure.

• / 4