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Question 1. Which of the following is most likely to cause excessive air restriction in a truck’s air induction system? A) Dirty air filter B) Faulty EGR valve C) Worn piston rings D) Low coolant level Answer: A Explanation: A dirty air filter restricts airflow into the engine, causing a drop in performance and efficiency. Question 2. What is the main function of a turbocharger in a diesel engine? A) Increase oil pressure B) Increase intake air pressure C) Decrease exhaust gas temperature D) Decrease coolant temperature Answer: B Explanation: A turbocharger compresses intake air, increasing its pressure and allowing more air (and fuel) into the engine for greater power. Question 3. Which component is responsible for maintaining the engine’s operating temperature within a specified range? A) Radiator
B) Thermostat C) Oil cooler D) Intercooler Answer: B Explanation: The thermostat regulates coolant flow to maintain the engine at its optimal operating temperature. Question 4. What can result from a stuck-closed thermostat? A) Engine overheating B) Low oil pressure C) Poor brake performance D) Air conditioning failure Answer: A Explanation: A stuck-closed thermostat prevents coolant from circulating, causing the engine to overheat. Question 5. Which procedure is most important before draining coolant from a truck’s cooling system? A) Disconnect the battery B) Allow the engine to cool C) Remove the air filter D) Depress the brake pedal
Question 8. Which component directly controls the amount of fuel delivered to each cylinder in a common rail diesel system? A) Fuel injectors B) Glow plugs C) Fuel tank D) EGR valve Answer: A Explanation: In common rail systems, injectors receive high-pressure fuel and control the exact amount injected into each cylinder. Question 9. When performing an oil change on a diesel truck, why is it important to use the manufacturer’s specified oil viscosity? A) Ensures proper lubrication under operating temperatures B) Prevents brake fade C) Reduces tire wear D) Increases battery life Answer: A Explanation: Correct oil viscosity ensures proper flow and lubrication, protecting engine components. Question 10. What is the function of an oil cooler in an engine lubrication system? A) Reduce oil temperature
B) Increase oil pressure C) Filter contaminants D) Add lubrication additives Answer: A Explanation: The oil cooler dissipates heat from the oil, maintaining optimal lubrication temperature. Question 11. Which sensor commonly provides input to the engine control module for ignition timing in gasoline engines? A) Crankshaft position sensor B) Oxygen sensor C) EGR temperature sensor D) Fuel temperature sensor Answer: A Explanation: The crankshaft position sensor monitors crankshaft position and speed, used to control ignition timing. Question 12. What is the primary purpose of a catalytic converter? A) Reduce harmful emissions B) Increase air intake C) Lower coolant temperature D) Boost fuel pressure
Question 15. Which diagnostic tool is most useful for retrieving DTCs from emission control systems? A) Scan tool B) Vacuum gauge C) Timing light D) Compression tester Answer: A Explanation: A scan tool communicates with the vehicle’s control modules to retrieve diagnostic trouble codes (DTCs). Question 16. What is the main function of cab air suspension in a truck? A) Improve driver comfort by isolating cab vibrations B) Increase engine power C) Enhance braking performance D) Reduce tire wear Answer: A Explanation: Cab air suspension absorbs road shocks and vibrations, improving comfort for the occupants. Question 17. If the cab ride height is too low, what should be checked first? A) Air springs and height control valve
B) Engine oil level C) Radiator cap D) Alternator output Answer: A Explanation: Low cab ride height often results from leaking air springs or a faulty height control valve. Question 18. Fiberglass is commonly used for truck hood construction because it is: A) Lightweight and corrosion-resistant B) Highly conductive C) Expensive and brittle D) Difficult to mold Answer: A Explanation: Fiberglass offers a good balance of strength, lightness, and resistance to corrosion, making it ideal for hoods. Question 19. What is the primary function of hood tilt cylinders? A) Assist with raising and lowering the hood B) Increase engine power C) Cool the radiator D) Filter air intake
Question 22. A truck’s A/C system is not cooling effectively. Which of the following is a likely cause? A) Low refrigerant charge B) High oil viscosity C) Faulty brake booster D) Shorted glow plug Answer: A Explanation: Insufficient refrigerant reduces the A/C system’s capacity to absorb heat, resulting in poor cooling. Question 23. R-134a is a type of: A) Refrigerant used in A/C systems B) Diesel fuel additive C) Engine oil D) Brake fluid Answer: A Explanation: R-134a has been the standard refrigerant in automotive climate control systems for many years. Question 24. What is the purpose of the receiver/drier in an A/C system? A) Remove moisture from the refrigerant
B) Increase refrigerant pressure C) Lubricate the compressor D) Cool incoming air Answer: A Explanation: The receiver/drier contains desiccant to absorb moisture and filters debris from the refrigerant. Question 25. In an electrical circuit, what does a relay typically do? A) Uses a small current to control a larger current B) Converts AC to DC C) Stores electrical energy D) Increases circuit resistance Answer: A Explanation: Relays allow a low-current control circuit to switch a high-current load safely. Question 26. A broken ground wire in a truck lighting circuit can cause: A) Lights to fail or behave erratically B) High oil pressure C) Excessive brake pedal travel D) Engine overheating Answer: A
Question 29. When testing battery voltage with the engine off, what is a typical reading for a fully charged 12V battery? A) 12.6 volts B) 10.5 volts C) 15.5 volts D) 9.6 volts Answer: A Explanation: A fully charged 12V battery should read about 12.6 volts at rest. Question 30. If a starter motor turns slowly but the battery tests good, what should be checked next? A) Starter solenoid and main cables for voltage drop B) Fuel pressure regulator C) Coolant thermostat D) A/C receiver/drier Answer: A Explanation: High resistance in the starter circuit (solenoid or cables) can cause slow cranking even with a good battery. Question 31. Which component stores operating parameters and controls engine and transmission functions? A) Electronic Control Module (ECM)
B) Oil pump C) Brake chamber D) Manual transmission shifter Answer: A Explanation: The ECM stores operational data and manages various engine and transmission functions through sensors and actuators. Question 32. What is the purpose of a diagnostic trouble code (DTC)? A) Identify a specific malfunction in a monitored system B) Measure engine oil pressure C) Adjust ride height D) Regulate fuel viscosity Answer: A Explanation: DTCs help technicians identify and troubleshoot faults in vehicle systems. Question 33. Which tool is used to measure resistance in an electrical circuit? A) Ohmmeter B) Fuel pressure gauge C) Torque wrench D) Dial indicator Answer: A
Question 36. Which color is commonly used to identify high voltage cables in hybrid/electric trucks? A) Orange B) Blue C) Green D) Black Answer: A Explanation: Orange is the industry standard for high voltage cables to warn technicians of potential danger. Question 37. What is the main hazard when working on high voltage systems in hybrid/electric trucks? A) Electrocution B) Low oil pressure C) Brake fade D) Radiator clogging Answer: A Explanation: High voltage systems carry lethal electric potential, making electrocution a primary risk. Question 38. What must be performed before servicing high voltage components? A) Lock-out/tag-out procedure
B) Brake fluid flush C) Oil pressure test D) Engine compression test Answer: A Explanation: Lock-out/tag-out ensures the system is de-energized and safe to work on. Question 39. When handling a hybrid truck, which label should you look for to confirm the presence of high voltage components? A) High voltage warning label B) Airbag deployment label C) Tire pressure label D) EGR flow label Answer: A Explanation: High voltage systems are marked with warning labels for technician safety. Question 40. What is the function of a height control valve in an air suspension system? A) Maintains proper ride height by adding or releasing air B) Controls engine oil pressure C) Regulates brake fluid flow
Explanation: Air suspension is most commonly used for the cab and rear axle to enhance ride quality. Question 43. What is the function of a kingpin on a truck’s steering system? A) Acts as the pivot point for steering knuckle movement B) Connects the driveshaft to the differential C) Holds the brake pads in place D) Supports the radiator Answer: A Explanation: The kingpin enables the steering knuckle to pivot, allowing the wheels to turn. Question 44. Which type of rim is most commonly used on heavy trucks? A) Steel disc wheel B) Composite wheel C) Aluminum spoke wheel D) Wooden wheel Answer: A Explanation: Steel disc wheels are strong, durable, and commonly used on heavy trucks. Question 45. Grease fittings (zerks) are used for:
A) Lubricating suspension and steering joints B) Adjusting brake shoes C) Topping off coolant D) Refilling air conditioning refrigerant Answer: A Explanation: Grease fittings provide access for lubricating suspension and steering components. Question 46. The master cylinder in a hydraulic brake system primarily: A) Converts pedal force to hydraulic pressure B) Filters brake fluid C) Cools the brake pads D) Supplies air to the brake chamber Answer: A Explanation: The master cylinder transforms mechanical pedal force into hydraulic pressure for braking. Question 47. What is the purpose of an air drier in an air brake system? A) Remove moisture from compressed air B) Increase brake fluid pressure C) Lubricate brake pads D) Filter engine oil
