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CDL Air Brakes Test practice questions

252 free questions with answers and explanations.

Practice test
  1. 1.A driver is performing a pre-trip inspection on a commercial vehicle equipped with an Anti-lock Braking System (ABS). After starting the engine, the ABS indicator light comes on and then goes out. What does this typically indicate?Air Brake System Parts
  2. 2.A driver is performing a pre-trip inspection and notices that the drain valves on the air storage tanks are missing. What is the immediate safety concern for the air brake system?Air Brake System Parts
  3. 3.During a pre-trip inspection, a driver notices that when the service brakes are applied, the brake chambers on the drive axle extend, but the brake shoes do not move away from the drums. What is the most likely cause of this issue?Air Brake System Parts
  4. 4.A technician is inspecting the air compressor on a commercial vehicle. They notice that the compressor's air intake filter is heavily clogged with dirt and debris. What is the most likely long-term consequence of operating the vehicle with such a condition?Air Brake System Parts
  5. 5.A technician is performing a diagnostic check on an air brake system. They notice that the air compressor is constantly running, but the system's air pressure never exceeds 80 psi. All connections appear secure, and there are no audible leaks. What is the most probable cause?Air Brake System Parts
  6. 6.A driver notices that the air compressor on their commercial vehicle is taking an unusually long time to build air pressure from 85 psi to 125 psi. After checking for external leaks, none are found. What internal component of the air compressor could be worn, causing this issue?Air Brake System Parts
  7. 7.A driver hears a continuous air leak coming from the area of the brake chambers, even when the service brakes are not applied. The air pressure is steadily dropping. Which component is most likely at fault?Air Brake System Parts
  8. 8.A driver is inspecting the air tanks on a commercial vehicle. They notice rust and pitting on the exterior surface of one of the air tanks. What is the most critical safety concern associated with this observation?Air Brake System Parts
  9. 9.When inspecting an air brake system, a driver should check that the safety relief valve on the air tank opens and releases air when the pressure reaches what specific range?Air Brake System Parts
  10. 10.A driver is inspecting the air tanks on a commercial vehicle. They notice that the check valve between the primary and secondary air tanks is stuck open. What consequence would this have on a dual air brake system?Air Brake System Parts
  11. 11.A driver notices that the air compressor cycles on and off more frequently than usual, even when not applying the brakes. The pressure gauges show that the system pressure drops from 125 psi to 100 psi, then the compressor cuts in and builds it back to 125 psi, only to drop again shortly after. What is the most probable cause?Air Brake System Parts
  12. 12.A driver observes that when they fully depress the brake pedal, the service brakes are slow to release, causing the vehicle to drag slightly. They verify that the slack adjusters are properly adjusted. What is the most likely cause of this issue?Air Brake System Parts
  13. 13.A driver is inspecting a commercial vehicle and observes that the front brake limiting valve is stuck in the 'slippery' position. What effect will this have on the vehicle's braking performance?Air Brake System Parts
  14. 14.A technician is performing a detailed inspection of a commercial vehicle's air brake system. They observe that the air compressor's unloader valves are not seating properly, causing a constant, faint hiss from the compressor head when the system is at cut-out pressure. What is the primary consequence of this condition?Air Brake System Parts
  15. 15.A technician is diagnosing an issue where a commercial vehicle's spring brakes are not releasing despite adequate air pressure in the system and the parking brake control knob being pushed in. The air compressor is building and maintaining proper pressure. What component is the most likely culprit?Air Brake System Parts
  16. 16.A driver performs a brake test and notes that the low air pressure warning light and buzzer activate when the air pressure drops to 55 psi. What action should the driver take?Air Brake System Parts
  17. 17.During a pre-trip inspection, a driver notices moisture and oil residue draining from the air tank's manual drain valve. What does this indicate?Air Brake System Parts
  18. 18.A driver observes that the supply pressure gauge for the primary air tank reads 120 psi, but the secondary air tank gauge reads only 80 psi. The air compressor is running normally. What is the most likely cause?Air Brake System Parts
  19. 19.A technician is troubleshooting a commercial vehicle's air brake system. They observe that the service brakes apply correctly, but the stop lights do not illuminate when the brake pedal is pressed. Where should the technician first investigate the issue?Air Brake System Parts
  20. 20.During a test, a driver fully applies the service brakes, and the stop light switch fails to activate the brake lights. What is the immediate safety concern?Air Brake System Parts
  21. 21.A driver is conducting a pre-trip inspection and notices that the air compressor is cycling on and off much more frequently than usual, even without heavy brake usage. The system pressure still builds to 125 psi and cuts out correctly. What is the most likely cause?Air Brake System Parts
  22. 22.A driver notices that when they fully depress the brake pedal, the service brakes are slow to respond and feel 'spongy'. However, the air pressure gauges show normal operating pressure. What is the most likely cause?Air Brake System Parts
  23. 23.A driver is conducting a pre-trip inspection on a commercial vehicle with a dual air brake system. They notice that the primary air tank gauge reads 125 psi, but the secondary air tank gauge reads 0 psi. There is no audible air leak. What is the most likely cause of this discrepancy?Air Brake System Parts
  24. 24.A driver is conducting a pre-trip inspection on a commercial vehicle equipped with an air brake system. What is the primary purpose of the supply pressure gauges?Air Brake System Parts
  25. 25.A driver is performing a pre-trip inspection on a commercial vehicle. They notice that when the parking brake control knob is pushed in, the spring brakes do not release. What is the most likely cause of this issue?Air Brake System Parts
  26. 26.A technician is performing maintenance on a commercial vehicle's air brake system. They are inspecting the spring brakes. What is the primary function of the spring brakes?Air Brake System Parts
  27. 27.During a pre-trip inspection, a driver notices that the air pressure in the system consistently builds from 85 psi to 100 psi in less than 45 seconds while the engine is at operating RPM. What does this indicate about the air compressor?Air Brake System Parts
  28. 28.A driver is conducting a pre-trip inspection of a commercial vehicle's air brake system. They notice that the supply pressure gauge for the primary air tank is fluctuating rapidly while the engine is running. What is the most likely cause of this fluctuation?Air Brake System Parts
  29. 29.A driver is inspecting the air tanks on a commercial vehicle. When draining the tanks, they notice a significant amount of oily water being expelled from the drain valves. What does this most likely indicate?Air Brake System Parts
  30. 30.During a road test, a driver finds that the service brakes are slow to release, causing the vehicle to drag slightly. The air pressure gauges indicate normal operating pressure. Which component is the most likely cause?Air Brake System Parts
  31. 31.During an air brake system inspection, a driver observes that the parking brake control knob is 'pulled out'. What does this indicate about the vehicle's braking status?Air Brake System Parts
  32. 32.An anti-lock braking system (ABS) indicator light stays on after the engine starts. What does this signify?Air Brake System Parts
  33. 33.A commercial vehicle is equipped with a dual air brake system. During a pre-trip inspection, a driver observes that the primary air tank gauge reads 90 psi, while the secondary air tank gauge reads 120 psi. The air compressor governor is set to cut out at 125 psi. What is the most likely cause of this discrepancy?Air Brake System Parts
  34. 34.A driver is operating a commercial vehicle and notices that the brake pedal requires significantly more travel than usual to achieve effective braking. The air pressure gauges indicate normal operating pressure. What is the most probable cause?Air Brake System Parts
  35. 35.A driver hears a continuous air leak coming from the area of the brake chambers even when the brakes are not applied. Which component is most likely malfunctioning?Air Brake System Parts
  36. 36.A driver is inspecting the front brake limiting valve on a commercial vehicle. They notice the control knob is in the 'wet' or 'slippery' position. What is the intended function of this position?Air Brake System Parts
  37. 37.A technician is performing a diagnostic check on a commercial vehicle's air brake system. They observe that the air compressor takes an unusually long time to build from 85 psi to 125 psi. Which of the following is the most likely cause?Air Brake System Parts
  38. 38.A driver is operating a commercial vehicle and notices that the service brakes feel 'spongy' and require greater pedal effort to achieve effective braking. During a visual inspection, they see no obvious air leaks. Which component is most likely contributing to this 'spongy' brake feel?Air Brake System Parts
  39. 39.A driver is operating a commercial vehicle and notices that the service brakes feel 'spongy' or require excessive pedal travel to achieve effective braking, even after adjusting the slack adjusters. What is the most likely cause of this symptom?Air Brake System Parts
  40. 40.A technician is inspecting the air brake system of a commercial truck and observes that the safety relief valve on an air tank is continuously releasing air, even though the supply pressure gauges indicate approximately 130 psi. What is the most likely cause of this issue?Air Brake System Parts
  41. 41.A technician is diagnosing an issue with a commercial vehicle's air brake system where the air compressor runs continuously, but the air pressure never exceeds 100 psi. What is the most likely cause?Air Brake System Parts
  42. 42.A driver is conducting a pre-trip inspection on a commercial vehicle equipped with an alcohol evaporator. They observe that the evaporator reservoir is empty. What is the primary purpose of adding alcohol to the air brake system?Air Brake System Parts
  43. 43.A driver notices that the air compressor on their commercial vehicle is taking an unusually long time to build air pressure from 0 psi to 100 psi, exceeding the typical 3-minute standard. What is the most probable cause?Air Brake System Parts
  44. 44.A technician is performing an inspection on an older commercial vehicle. The vehicle is equipped with an alcohol evaporator. What is the primary function of this component?Air Brake System Parts
  45. 45.A driver is performing a pre-trip inspection on a commercial vehicle. When they fully apply the service brakes, they notice that the brake pedal has an excessive amount of free play before the brakes begin to engage. What is the most likely cause of this issue?Air Brake System Parts
  46. 46.A driver is inspecting a commercial vehicle and finds that the front brake limiting valve is set to 'slippery'. What is the purpose of this setting in an air brake system?Air Brake System Parts
  47. 47.A driver notices that the air compressor is continuously running, but the air pressure gauges are not increasing beyond 80 psi. Which component is most likely malfunctioning?Air Brake System Parts
  48. 48.A driver is performing an emergency stop in a commercial vehicle equipped with an Anti-lock Braking System (ABS). The driver notices that the brake pedal pulses rapidly under their foot. What does this indicate?Air Brake System Parts
  49. 49.A driver is performing a brake test on a commercial vehicle. When applying the service brakes, they notice that the brake pedal feels unusually 'spongy' or soft, requiring more effort than usual to slow the vehicle. The air pressure gauges indicate normal operating pressure. What is the most likely underlying problem?Air Brake System Parts
  50. 50.A driver is performing a pre-trip inspection on a commercial vehicle with a dual air brake system. They observe that when the parking brake is set, the spring brakes activate, but the parking brake control knob does not 'pop out' automatically. What does this indicate?Air Brake System Parts