CDL Air Brakes Test practice questions
252 free questions with answers and explanations.
- 101.A driver performs a brake test and notes that the red low air pressure warning light and buzzer come on at 70 psi and turn off at 80 psi. What does this indicate about the low air pressure warning system?Air Brake System Parts
- 102.During a pre-trip inspection, a driver notices that when the service brakes are applied, the pushrod on one of the brake chambers moves less than 1/2 inch. What does this likely indicate?Air Brake System Parts
- 103.A driver is performing a pre-trip inspection and observes that the brake pedal, when pressed, operates smoothly and returns quickly to its original position. There are no unusual sounds or air leaks around the pedal area. What does this indicate about the brake pedal (foot) valve?Air Brake System Parts
- 104.A technician is diagnosing an issue where the stop lights on a commercial vehicle with air brakes are not illuminating when the service brake pedal is pressed. Which specific component should be inspected first?Air Brake System Parts
- 105.A driver observes that when they release the parking brake control knob, the spring brakes do not release. The supply pressure gauges indicate full system pressure (125 psi). What is the most likely cause?Air Brake System Parts
- 106.A commercial vehicle driver is performing a pre-trip inspection. After charging the system to full pressure, they turn off the engine and observe a continuous, audible air leak coming from the area of the brake pedal. What does this most likely indicate?Air Brake System Parts
- 107.A driver is inspecting the air storage tanks on a commercial vehicle. They notice significant rust and pitting on the exterior of one of the tanks. What is the most appropriate action to take?Air Brake System Parts
- 108.A technician is diagnosing an issue with a truck's air brake system where the brake pedal feels spongy and requires excessive travel to achieve braking. The supply pressure gauges indicate normal operating pressure. Which component is the most likely cause?Air Brake System Parts
- 109.A driver performs a pre-trip inspection and observes that the parking brake control knob pops out automatically when the air pressure in the system drops below 40 psi. What does this indicate?Air Brake System Parts
- 110.A driver notices that the air pressure gauge for the primary air tank is showing 60 psi, while the secondary tank gauge shows 100 psi. What is the most likely cause of this discrepancy in a dual air brake system?Air Brake System Parts
- 111.A driver notices that the air compressor cycles on and off more frequently than usual, even when the vehicle is not being driven or using air accessories. What is the most likely cause?Air Brake System Parts
- 112.A driver is conducting a pre-trip inspection of a commercial vehicle's air brake system. They notice that the air compressor is engaged and building pressure, but the supply pressure gauges are not showing any increase in air pressure. Which component is most likely malfunctioning?Air Brake System Parts
- 113.A driver is performing a pre-trip inspection on a vehicle equipped with air brakes. After ensuring the air system is fully charged, the driver applies the service brake and holds it for one minute. The air pressure gauge should not drop more than what amount for a single unit vehicle?Inspecting Air Brake Systems
- 114.A driver is performing a pre-trip inspection on a vehicle with air brakes. The vehicle has three air tanks. How often should the moisture and contaminants be drained from these air tanks?Inspecting Air Brake Systems
- 115.During a pre-trip inspection, a driver performs the low air pressure warning test. The low air pressure warning device should activate when the air pressure in the tanks drops to no less than what PSI?Inspecting Air Brake Systems
- 116.A driver is conducting a pre-trip inspection. After fully charging the air system (125 psi), the engine is turned off, and the parking brake is released. The driver then applies the service brake fully for one minute. What is the maximum allowable air pressure drop for a combination vehicle during this test?Inspecting Air Brake Systems
- 117.During a pre-trip inspection, a driver checks the air pressure gauge. After starting the engine, the air pressure should build from 85 psi to 100 psi within what maximum time frame for a dual air system?Inspecting Air Brake Systems
- 118.A driver is performing a pre-trip inspection. The vehicle is equipped with a 'wig-wag' type low air pressure warning device. At what approximate air pressure should this device activate?Inspecting Air Brake Systems
- 119.During a pre-trip inspection, a driver checks the spring brakes. Which of the following statements is true regarding the function of spring brakes?Inspecting Air Brake Systems
- 120.A technician is inspecting the air compressor on a commercial vehicle. They notice that the compressor's discharge line, connecting to the wet tank, is excessively hot to the touch. What does this condition most likely indicate?Inspecting Air Brake Systems
- 121.A driver is performing a pre-trip inspection and notices that the air compressor drive belt is cracked and frayed. The air pressure gauge is showing a healthy 120 psi. What is the most appropriate action for the driver to take?Inspecting Air Brake Systems
- 122.A driver is performing a pre-trip inspection on a vehicle equipped with air brakes. After building air pressure to 125 psi, the driver turns off the engine, releases the parking brake, and applies full service brakes. The driver observes the air pressure gauge for one minute. What is the maximum allowable air pressure drop for a combination vehicle during this test?Inspecting Air Brake Systems
- 123.A driver is performing a pre-trip inspection. They notice that the air dryer's purge cycle is excessively frequent (e.g., every 15-20 seconds) even after the system has fully charged. What is the most likely cause of this condition?Inspecting Air Brake Systems
- 124.During a pre-trip inspection of an air brake system, a driver notices that the air compressor is cycling on and off more frequently than usual, even when there are no significant air leaks. What could this frequent cycling indicate?Inspecting Air Brake Systems
- 125.A technician is troubleshooting an air brake system where the air dryer continuously purges even when the system pressure is stable and full. What is the most likely cause?Inspecting Air Brake Systems
- 126.A driver is performing a pre-trip inspection and notices that the spring brakes on the vehicle do not apply when the air pressure drops below 20 psi. What is the most likely cause?Inspecting Air Brake Systems
- 127.During a pre-trip inspection, a driver observes that the brake pushrod on a service brake chamber extends by 1 1/2 inches when the service brakes are fully applied. The brake chamber is a Type 30. What does this indicate?Inspecting Air Brake Systems
- 128.A driver is inspecting the brake drums on a commercial vehicle. Which of the following conditions would indicate an immediate 'out-of-service' defect?Inspecting Air Brake Systems
- 129.A driver is conducting a pre-trip inspection and notices moisture, but no oil, consistently being expelled from the air dryer's purge valve. What does this condition primarily suggest?Inspecting Air Brake Systems
- 130.A driver is performing a pre-trip inspection on a vehicle with air brakes. They notice that when the parking brake is applied, the vehicle still rolls slightly on a level surface. What is the most likely cause?Inspecting Air Brake Systems
- 131.During a pre-trip inspection, a driver observes that the automatic slack adjusters on a vehicle require manual adjustment. What does this indicate?Inspecting Air Brake Systems
- 132.A driver is performing a pre-trip inspection. They notice that the air pressure gauge shows a steady 125 psi, but the air compressor cycles on and off much more frequently than usual, even without heavy braking. What is the most likely issue?Inspecting Air Brake Systems
- 133.During a pre-trip inspection, a driver performs a static air leak test (engine off, parking brake applied). After the initial pressure drop, the air pressure gauge shows a steady 120 psi. After one minute, the pressure has dropped to 117 psi. The vehicle is a single unit truck. What does this indicate?Inspecting Air Brake Systems
- 134.A technician is inspecting the air tanks on a commercial vehicle. They notice that the primary (supply) tank is accumulating significantly more moisture and contaminants than the secondary (service) tank. What does this most likely suggest about the air dryer?Inspecting Air Brake Systems
- 135.A driver is inspecting the brake linings on a commercial vehicle with air brakes. Which of the following conditions would require immediate attention and likely brake replacement?Inspecting Air Brake Systems
- 136.A technician is performing a brake adjustment check on a Type 30 long stroke air brake chamber. The maximum allowable pushrod stroke for this chamber is 2.0 inches. If the technician measures a stroke of 2.25 inches, what is the correct action?Inspecting Air Brake Systems
- 137.During a pre-trip inspection, a driver performs a static air leak test (engine off, parking brake applied). After the initial pressure drop, the air pressure should not drop more than what amount in one minute for a straight truck or bus?Inspecting Air Brake Systems
- 138.A driver notices that the air pressure gauge shows a steady 125 psi, but the low air warning light is illuminated. The driver has already confirmed the gauge is accurate. What is the most likely cause of this discrepancy?Inspecting Air Brake Systems
- 139.A driver is inspecting the air lines on a commercial vehicle. Which of the following conditions is considered acceptable?Inspecting Air Brake Systems
- 140.A driver is performing a pre-trip inspection on a vehicle with air brakes. They notice that the brake pedal feels spongy or soft when pressed, even though the air pressure gauge shows normal operating pressure. What is the most likely cause?Inspecting Air Brake Systems
- 141.A driver is performing a pre-trip inspection on a vehicle equipped with automatic slack adjusters. Which of the following is the correct procedure for checking the adjustment of these slack adjusters?Inspecting Air Brake Systems
- 142.A driver is performing a pre-trip inspection and observes that the spring brakes on the vehicle do not apply automatically when the air pressure drops below 20 psi. What is the most likely cause of this issue?Inspecting Air Brake Systems
- 143.A technician is inspecting a vehicle's air brake system and observes that the brake chambers at one axle have significantly different pushrod travel when the service brakes are applied. One chamber shows 1 inch of travel, while the other shows 2.5 inches. The maximum allowable pushrod travel for this type of chamber is 2 inches. What is the most appropriate conclusion?Inspecting Air Brake Systems
- 144.A driver is checking the brake drums on a vehicle equipped with air brakes. Which of the following conditions, if found, would NOT immediately render the vehicle out of service for brake drum issues?Inspecting Air Brake Systems
- 145.A driver is performing a pre-trip inspection. They notice that the air dryer continuously purges (releases air) at short, irregular intervals, even when the air system is fully charged. What is the most likely cause of this behavior?Inspecting Air Brake Systems
- 146.A driver is inspecting the air lines on a commercial vehicle. Which of the following conditions in an air line is considered the most critical defect requiring immediate attention?Inspecting Air Brake Systems
- 147.During a pre-trip inspection, a driver observes that the air pressure gauge shows 100 psi. When the brake pedal is fully depressed and held for one minute, the pressure drops to 95 psi. The vehicle is a single unit truck. What does this indicate?Inspecting Air Brake Systems
- 148.A driver observes that the slack adjusters on several wheels of a tandem axle trailer are beyond their adjustment limits. The brakes are out of adjustment. If the driver continues to operate the vehicle, what is the most significant immediate consequence?Inspecting Air Brake Systems
- 149.During a pre-trip inspection, a driver notices that the air pressure gauge shows a rapid drop immediately after applying the service brakes and holding them. What does this most likely indicate?Inspecting Air Brake Systems
- 150.A driver is performing a pre-trip inspection on a vehicle equipped with air brakes. When checking the air compressor, what is the minimum tension requirement for its drive belt?Inspecting Air Brake Systems