I85PREP
⌘ K
NE CDL Air Brakes study materials
NE CDL Air Brakes study resources

NE CDL Air Brakes practice questions

One question at a time. Build your NE CDL Air Brakes understanding.

First 50 of 199 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Air Brake System Components and Operation

In a typical air brake system, what is the function of the compressor governor?

  1. It converts electrical signals from the treadle into air pressure
  2. It limits the maximum braking force delivered to the rear service chambers
  3. It controls when the compressor cuts in and out to maintain system air pressure Correct answer.
  4. It drains moisture from the supply reservoir each time the brakes are applied

Explanation

The governor senses supply-tank pressure and starts or stops the compressor so pressure stays within a set range, typically cutting out near 120-125 psi and cutting in near 100 psi. It is a pressure-sensing control device, not a moisture or braking-force device.

Question 2Air Brake System Components and Operation

What is the primary purpose of the supply reservoir in an air brake system?

  1. To store compressed air for the system and provide a reserve if the compressor fails Correct answer.
  2. To hold air only for the front brakes so they release faster
  3. To collect water and oil so they never reach the rest of the system
  4. To smooth out pressure pulses from the treadle valve

Explanation

The supply (wet) reservoir receives air directly from the compressor and stores it so the system has capacity and a reserve. If the compressor stops, stored air still allows several brake applications.

Question 3Air Brake System Components and Operation

A driver notices the low-air warning buzzer sounds and the pressure gauge reads about 60 psi. What does this indicate about the system?

  1. The air dryer is in its purge cycle and pressure will return automatically
  2. The compressor is overcharging and the governor has failed closed
  3. The system pressure has dropped below a safe operating level and brakes may not apply fully Correct answer.
  4. The spring brakes have fully released and the system is functioning normally

Explanation

The low-air warning activates when pressure falls below a safe threshold, usually around 60 psi, warning that braking performance is compromised. The driver should stop safely and let pressure build before continuing.

Question 4Air Brake System Components and Operation

What component physically applies the parking brake on a vehicle with spring brakes when air pressure is released?

  1. The quick-release valve diaphragm
  2. The service brake chamber pushrod
  3. The relay valve's balance piston
  4. The spring brake chamber's large coil spring Correct answer.

Explanation

Spring brake chambers contain a large coil spring that applies the brake when air pressure is removed from the spring cavity. This is why a loss of air pressure causes the parking brake to set automatically.

Question 5Air Brake System Components and Operation

Which device protects the system so that a failure in one circuit does not drain air from the other circuits?

  1. The safety valve
  2. The pressure protection valve or double check valve arrangement Correct answer.
  3. The low-pressure indicator switch
  4. The alcohol evaporator

Explanation

Protection valves and double check valves isolate circuits so a leak in one circuit does not deplete the others. This preserves braking capability in the remaining circuits after a failure.

Question 6Air Brake System Components and Operation

During a static leak test, the driver fully applies the brakes and holds them. What is being checked?

  1. Compressor cut-in pressure
  2. Governor cut-out setting
  3. Static leakage in the applied brake system Correct answer.
  4. Air dryer purge timing

Explanation

Holding a full brake application with the engine off and watching the gauge reveals static leaks in the applied system. A steady pressure drop beyond the allowed rate indicates a leak that must be repaired.

Question 7Air Brake System Components and Operation

What does the alcohol evaporator do in an air brake system?

  1. It lubricates the brake chamber pushrods
  2. It removes oil from the compressor discharge
  3. It adds alcohol vapor to the air to help prevent moisture from freezing in valves and lines Correct answer.
  4. It raises the compressor cut-out pressure

Explanation

An alcohol evaporator introduces alcohol vapor into the air system so that condensed moisture is less likely to freeze in valves and lines during cold weather. It does not remove oil or change pressure settings.

Question 8Air Brake System Components and Operation

A driver performs a compressor check: with the engine running and pressure built up, the compressor should cut out at approximately what pressure?

  1. 120 to 125 psi Correct answer.
  2. 150 to 160 psi
  3. 80 to 90 psi
  4. 100 to 110 psi

Explanation

Most highway air brake systems are governed to cut out around 120 to 125 psi and cut in around 100 psi. This range provides adequate reserve while staying within safe limits.

Question 9Air Brake System Components and Operation

When the driver presses the brake treadle, which component delivers air from the reservoir to the rear service chambers in response to a control signal?

  1. The safety valve
  2. The quick-release valve
  3. The inversion valve
  4. The relay valve Correct answer.

Explanation

A relay valve uses a small control signal from the foot valve to open and deliver reservoir air directly to the rear chambers. This shortens response time by avoiding a long control line carrying full volume.

Question 10Air Brake System Components and Operation

What is the purpose of the air dryer in an air brake system?

  1. To regulate the cut-in and cut-out pressures
  2. To provide a reserve of air for the parking brake
  3. To increase the compressor's delivery pressure
  4. To remove moisture and contaminants from the compressed air before it reaches the reservoirs Correct answer.

Explanation

The air dryer uses a desiccant to absorb moisture and trap contaminants from compressor discharge air. Dry air reduces corrosion and prevents freeze-ups in valves and lines.

Question 11Air Brake System Components and Operation

A driver observes that the air pressure gauge shows a slow but steady drop while the brakes are released and the engine is off. What is the most likely explanation?

  1. A leak in the system's charged (unapplied) circuit Correct answer.
  2. The air dryer is purging
  3. The governor is cutting out too soon
  4. Normal compressor cycling

Explanation

With the brakes released and the engine off, a steady pressure drop indicates leakage in the charged portion of the system. The driver should identify and repair the leak before operating the vehicle.

Question 12Air Brake System Components and Operation

What is the role of the safety valve on the supply reservoir?

  1. It releases air if system pressure exceeds a safe maximum Correct answer.
  2. It drains condensate automatically each cycle
  3. It allows air to bypass the governor during startup
  4. It releases air to apply the spring brakes

Explanation

The safety valve is a pressure-relief device that opens if pressure rises above a safe maximum, protecting tanks and components from overpressure. It is a backup to the governor, not a normal control.

Question 13Air Brake System Components and Operation

A driver must test the service brakes before a trip. Which observation best confirms the service brakes are functioning?

  1. The vehicle slows and stops when the foot brake is applied with normal pedal effort Correct answer.
  2. The vehicle holds still with the parking brake applied on a level surface
  3. The compressor cuts out at the governed pressure
  4. The low-air buzzer sounds when the engine is started

Explanation

A service brake test confirms that applying the foot brake produces normal deceleration and stopping. This verifies that the treadle, valving, and chambers are delivering braking force.

Question 14Air Brake System Components and Operation

In a dual-circuit air brake system, why are the circuits separated?

  1. To allow the parking brake to operate independently of the service brake
  2. To provide braking capability if one circuit fails Correct answer.
  3. To allow different pressures in front and rear brakes
  4. To reduce the number of reservoirs needed

Explanation

Dual circuits are separated so that a failure in one circuit does not disable the other, preserving partial braking. Protection valves and separate reservoirs support this redundancy.

Question 15Air Brake System Components and Operation

A spring brake chamber has its spring cavity pressurized to release the parking brake. What happens if the air line to that chamber is cut?

  1. The brake remains released until the driver pulls the parking valve
  2. The chamber fills with air from the other circuit and stays released
  3. The brake releases fully and the vehicle rolls
  4. The brake applies because spring pressure is no longer held off Correct answer.

Explanation

Spring brakes are held off by air pressure; if that pressure is lost, the spring applies the brake. A cut line therefore causes the parking brake to set, which is the fail-safe design intent.

Question 16Air Brake System Components and Operation

What is the function of the quick-release valve in a rear brake circuit?

  1. It rapidly fills the service chamber when the brake is applied
  2. It limits pressure to the front chambers
  3. It rapidly exhausts service chamber air when the brake is released Correct answer.
  4. It releases the spring brake when pressure is lost

Explanation

A quick-release valve is located near the chambers and exhausts air quickly when the treadle is released. This speeds brake release and reduces the lag caused by long lines back to the foot valve.

Question 17Air Brake System Components and Operation

During a compressor build-up test, the pressure rises from 85 to 100 psi in about 40 seconds at governed engine speed. What does this indicate?

  1. The compressor is building pressure within a normal acceptable range Correct answer.
  2. The governor is set too high
  3. The compressor is failing and must be replaced immediately
  4. The air dryer desiccant is exhausted

Explanation

A typical build-up test expects pressure to rise from 85 to 100 psi within about 45 seconds at fast idle. A 40-second rise falls within that acceptable window, indicating normal compressor performance.

Question 18Air Brake System Components and Operation

What does the inversion valve do in a spring brake system?

  1. It reverses the direction of airflow in the supply reservoir
  2. It inverts the treadle signal to increase rear braking force
  3. It reverses the control signal so that a loss of pressure can still release or modulate the spring brakes Correct answer.
  4. It converts the air dryer purge signal into a drain cycle

Explanation

An inversion valve provides a modulated spring brake application or release when service air is lost, allowing controlled braking rather than a sudden full spring application. It inverts the normal control logic for safety.

Question 19Air Brake System Components and Operation

A vehicle with spring brakes will not release after the parking valve is pushed in. Which condition is most consistent with this symptom?

  1. The governor cut-out pressure is too low
  2. The spring cavities are not receiving release pressure due to a blocked line or faulty valve Correct answer.
  3. The service chambers are receiving too much application pressure
  4. The low-pressure warning switch has failed

Explanation

Spring brakes release only when air pressure reaches the spring cavity. A blocked line, faulty parking valve, or failed relay can prevent release pressure from arriving, leaving the brakes applied.

Question 20Air Brake System Components and Operation

Why does a relay valve improve brake response on a long-wheelbase vehicle?

  1. It increases the governor cut-out pressure to shorten build time
  2. It bypasses the foot valve entirely during normal braking
  3. It removes moisture from the control line before delivery
  4. It shortens the distance air must travel by using reservoir air near the chambers under a small control signal Correct answer.

Explanation

A relay valve is mounted near the chambers and delivers reservoir air locally when triggered by a small control signal from the foot valve. This reduces the volume that must travel the length of the vehicle, shortening application time.

Question 21Air Brake System Components and Operation

A driver reports that the low-air warning and the spring brakes engage at about 45 psi while the gauge still shows pressure. Which explanation best fits?

  1. The safety valve is stuck open and venting the supply tank
  2. The warning switch and spring brake control are functioning at their designed thresholds, and the remaining pressure is insufficient for full service braking Correct answer.
  3. The air dryer is purging and temporarily dropping pressure
  4. The governor is overcharging the system and forcing the spring brakes on

Explanation

Low-air warnings typically activate around 60 psi and spring brakes begin to apply as pressure continues to fall. At 45 psi the remaining air is insufficient for reliable service braking, so the warning and spring application are expected safety behavior.

Question 22Air Brake System Components and Operation

Which statement correctly describes the relationship between the service brake and the spring brake in a typical chamber?

  1. The spring brake applies only when the service brake is also applied
  2. The service chamber holds the parking brake off while the spring chamber provides service braking
  3. They share one pushrod, with the service chamber applying via air pressure and the spring chamber applying via spring force when air is released Correct answer.
  4. They operate on separate pushrods that act on different brake shoes

Explanation

In a typical spring brake chamber, the service section applies the brake with air pressure and the spring section applies it with spring force when release air is removed. Both act through the same pushrod to stroke the slack adjuster.

Question 23Air Brake System Components and Operation

What is the purpose of the pressure protection valve in a multi-circuit system?

  1. It automatically drains the wet tank
  2. It signals the governor to increase cut-out pressure
  3. It limits maximum pressure to the front brakes
  4. It closes off a failed circuit so the remaining circuits can maintain pressure Correct answer.

Explanation

A pressure protection valve isolates a circuit that has lost pressure, preventing it from draining the other circuits. This preserves air for the remaining service brakes.

Question 24Air Brake System Components and Operation

A driver performs the spring brake test by pulling the parking valve with the engine off. What should happen?

  1. The parking brake should set and hold the vehicle Correct answer.
  2. The service brakes should apply automatically
  3. The low-air buzzer should sound continuously
  4. The pressure gauge should drop to zero immediately

Explanation

Pulling the parking valve releases air from the spring cavities, allowing the spring to apply and hold the vehicle. This confirms the spring brake system is functioning.

Question 25Air Brake System Components and Operation

Which component converts the driver's foot pressure into a variable air signal that controls the brakes?

  1. The air dryer
  2. The foot valve (treadle valve) Correct answer.
  3. The governor
  4. The safety valve

Explanation

The foot valve, or treadle valve, meters air pressure in proportion to pedal travel and sends that signal to the relay valves or chambers. It is the driver's primary control of service braking.

Question 26Air Brake System Components and Operation

Which component stores the compressed air that the brake system uses after the compressor has stopped building pressure?

  1. The slack adjuster
  2. The governor
  3. The supply reservoir Correct answer.
  4. The treadle valve

Explanation

Reservoirs are storage tanks that hold compressed air so brakes can be applied repeatedly even when the compressor is not building pressure. The governor only controls compressor cycling, the treadle valve meters air, and the slack adjuster transfers pushrod stroke to the brake shoes.

Question 27Air Brake System Components and Operation

What is the function of the governor in a compressor-equipped air brake system?

  1. It limits the maximum pressure delivered to the service chambers
  2. It drains moisture from the lowest point of the system
  3. It regulates compressor loading and unloading between preset cut-in and cut-out pressures Correct answer.
  4. It balances pressure between the primary and secondary circuits

Explanation

The governor monitors supply reservoir pressure and tells the compressor when to pump (cut-in) and when to stop (cut-out). This cycling keeps system pressure within the designed operating range.

Question 28Air Brake System Components and Operation

A driver hears a brief burst of air escaping near the compressor area each time the system reaches full pressure. Which component is most likely releasing that air?

  1. The compressor unloader mechanism Correct answer.
  2. The safety valve on the wet tank
  3. The low-pressure warning buzzer
  4. The quick-release valve

Explanation

When the governor reaches cut-out, it signals the compressor unloader to hold the inlet valves open so the compressor stops pumping, and the trapped air is released. This produces the characteristic short purge near the compressor.

Question 29Air Brake System Components and Operation

Which statement best describes the function of the supply reservoir (wet tank) in a typical air brake system?

  1. It holds the air that applies the front service brakes only
  2. It receives air directly from the compressor and lets moisture and oil drop out before air moves to the other circuits Correct answer.
  3. It stores air only for the low-pressure warning system
  4. It provides the signal air that operates the parking brake valve

Explanation

The supply or wet tank is the first tank downstream of the compressor, so it collects the hottest, dirtiest air and allows condensate and oil to settle. From there air passes through check valves to the primary and secondary circuits.

Question 30Air Brake System Components and Operation

A driver notices the air pressure gauge climbing very slowly and the compressor seems to run constantly without reaching cut-out. Which condition is most consistent with these symptoms?

  1. A governor stuck in the unloaded position at low pressure
  2. A significant leak or a worn compressor that cannot build pressure Correct answer.
  3. A properly functioning system at governed speed
  4. A safety valve opening at normal operating pressure

Explanation

Slow, continuous build-up that never reaches cut-out points to air escaping somewhere or a compressor that cannot keep up. A healthy system reaches governed pressure within the time specified by the manufacturer.

Question 31Air Brake System Components and Operation

What is the purpose of a drain valve installed at the bottom of an air reservoir?

  1. To adjust the cut-out pressure of the governor
  2. To supply air to the low-pressure indicator
  3. To release air pressure quickly during a brake application
  4. To remove accumulated water and oil from the tank Correct answer.

Explanation

Moisture condenses inside reservoirs, and oil from the compressor can collect there as well. Draining each tank daily, or as the manufacturer specifies, removes this contamination before it reaches valves and chambers.

Question 32Air Brake System Components and Operation

Which component reduces the pressure delivered to the front service brake chambers compared with full reservoir pressure?

  1. The relay valve
  2. The alcohol evaporator
  3. The front brake limiting valve or proportioning valve Correct answer.
  4. The inversion valve

Explanation

A limiting or proportioning valve reduces front brake application pressure under certain conditions to help preserve steering control on slippery surfaces. It is located in the front brake circuit.

Question 33Air Brake System Components and Operation

When the driver releases the brake treadle, what should happen to the air in the service brake chambers?

  1. It should exhaust to the atmosphere, allowing the spring and return springs to release the brakes Correct answer.
  2. It should transfer to the spring brake cavity to hold the brakes off
  3. It should return to the supply reservoir for reuse
  4. It should remain in the chambers until the next application

Explanation

Releasing the treadle closes the delivery port and opens the exhaust port so chamber air vents to atmosphere. With the pressure gone, the return springs and the mechanical release of the brake pull the shoes away from the drums.

Question 34Air Brake System Components and Operation

A driver applies the brakes and hears a steady hiss that continues as long as the pedal is held. Which condition should the driver suspect?

  1. A leaking service chamber, line, or valve on the applied side Correct answer.
  2. The safety valve venting excess pressure
  3. The compressor unloader operating
  4. Normal exhaust from the quick-release valve

Explanation

A continuous hiss while the brakes are held indicates air escaping from a pressurized component such as a chamber diaphragm, hose, or fitting. Normal exhaust occurs only briefly at application or release.

Question 35Air Brake System Components and Operation

What does the application of the parking brake control valve do to a spring brake chamber?

  1. It adds air to the spring cavity to force the parking brake on
  2. It blocks the service chamber from receiving air permanently
  3. It exhausts air from the spring cavity, allowing the spring to apply the parking brake Correct answer.
  4. It opens the reservoir drain to relieve pressure

Explanation

Spring brakes are held off by air pressure compressing the spring. Pulling the parking valve exhausts that air, so the spring extends and applies the brake mechanically.

Question 36Air Brake System Components and Operation

Which component prevents air from one circuit of a dual-circuit system from flowing back into the other circuit?

  1. The check valve between the circuits Correct answer.
  2. The quick-release valve
  3. The low-pressure switch
  4. The slack adjuster

Explanation

Check valves allow air to flow in one direction only, so a failure or leak in one circuit cannot drain the other. This keeps at least partial braking available if one circuit fails.

Question 37Air Brake System Components and Operation

During a pre-trip inspection, the driver finds that the low-pressure warning activates at about 60 psi. What does this indicate?

  1. The warning is activating at a typical low-pressure threshold, subject to the manufacturer's specification Correct answer.
  2. The warning should never activate while the engine is running
  3. The warning is operating normally because it should activate near cut-out pressure
  4. The warning switch is disconnected

Explanation

A low-air warning at about 60 psi is ordinarily normal and warns the driver before pressure falls far enough for spring brakes to apply. This is a low-pressure threshold, separate from compressor cut-out. The manufacturer's specification controls, and some buses warn at higher pressures.

Question 38Air Brake System Components and Operation

What is the primary purpose of the slack adjuster in an air brake system?

  1. It converts pushrod linear travel into rotary motion that applies the brake shoes Correct answer.
  2. It regulates the compressor cut-in pressure
  3. It vents moisture from the service chamber
  4. It stores air for the service brake application

Explanation

The slack adjuster is a lever arm on the camshaft that turns pushrod stroke into rotation of the S-cam or wedge. Automatic versions also maintain proper shoe-to-drum clearance.

Question 39Air Brake System Components and Operation

A driver checks pushrod stroke and finds it well beyond the adjustment limit on one chamber. What is the most likely consequence if the vehicle is driven?

  1. The brake on that wheel may apply weakly or not at all because the chamber runs out of stroke Correct answer.
  2. The low-pressure warning will activate to signal the condition
  3. The governor will raise cut-out pressure to compensate
  4. The spring brake will release automatically to compensate

Explanation

Excessive pushrod stroke means the chamber uses most of its travel before the shoes contact the drum, leaving little force for braking. This is why stroke must be checked and adjusted to the manufacturer's limit.

Question 40Air Brake System Components and Operation

Which component provides a modulated air signal to the trailer brakes when the driver applies the foot valve?

  1. The trailer spring brake chamber
  2. The trailer hand valve or the tractor protection system delivery line Correct answer.
  3. The compressor discharge line
  4. The supply reservoir drain

Explanation

The foot valve sends a control signal through the tractor protection valve to the trailer, and a trailer hand valve can apply the trailer brakes independently. This signal modulates trailer brake application with the tractor.

Question 41Air Brake System Components and Operation

What happens in a dual-circuit system if the primary circuit loses pressure?

  1. The secondary circuit continues to supply air so the driver retains partial braking Correct answer.
  2. The spring brakes release automatically to allow steering
  3. Both circuits lose pressure because they share a common reservoir
  4. The compressor stops running until the leak is repaired

Explanation

The two circuits are isolated by check valves and separate tanks so a failure in one does not drain the other. The driver keeps braking through the intact circuit, though stopping distance may increase.

Question 42Air Brake System Components and Operation

Which device automatically expels moisture and contaminants from the air system during normal operation?

  1. The relay valve
  2. The air dryer with its purge cycle Correct answer.
  3. The safety valve
  4. The inversion valve

Explanation

An air dryer uses a desiccant to remove water vapor and then purges collected moisture to atmosphere during its cycle. This reduces condensate reaching the reservoirs and valves.

Question 43Air Brake System Components and Operation

A driver notices that the rear brakes apply noticeably later than the front brakes on a long tractor-trailer. Which component is most likely involved?

  1. The front limiting valve set too low
  2. The alcohol evaporator running continuously
  3. A faulty relay valve or restricted line in the rear circuit Correct answer.
  4. The governor cut-in pressure set too high

Explanation

Relay valves use reservoir air close to the chambers to speed application, so a sticking relay or a restricted line delays rear brake timing. Balanced brake timing is essential for stability during stops.

Question 44Air Brake System Components and Operation

What is the function of the tractor protection valve?

  1. It closes the trailer supply line if pressure drops, preventing trailer air loss and applying trailer spring brakes Correct answer.
  2. It adjusts slack on the trailer brakes
  3. It regulates the compressor's cut-out pressure
  4. It drains the trailer reservoirs automatically

Explanation

The tractor protection valve isolates the trailer if tractor pressure falls too low or the supply line separates. This preserves tractor air and causes the trailer spring brakes to apply for safety.

Question 45Air Brake System Components and Operation

During a compressor check, the driver observes that pressure builds from 85 to 100 psi in about 50 seconds at fast idle. How should this be interpreted?

  1. The governor is stuck open and venting air
  2. The system has a major leak that must be repaired before moving
  3. The build-up time is within typical specifications and the compressor is performing adequately Correct answer.
  4. The compressor is failing because build-up should take under 10 seconds

Explanation

Typical specifications call for build-up from about 85 to 100 psi in roughly 30 to 90 seconds at governed engine speed, depending on the manufacturer. A 50-second result falls in that range.

Question 46Air Brake System Components and Operation

Which component senses the driver's pedal force and meters air delivery proportionally to that force?

  1. The drain valve
  2. The safety valve
  3. The foot valve (treadle valve) Correct answer.
  4. The spring brake chamber

Explanation

The foot or treadle valve is the primary control: pedal force positions a valve that admits reservoir air in proportion to demand. Releasing the pedal exhausts the delivery air.

Question 47Air Brake System Components and Operation

A driver finds that the parking brake will not release even though the parking valve is pushed in and the gauge shows normal pressure. Which condition is most likely?

  1. A leak in the service chamber diaphragm
  2. A governor set to cut out too low
  3. A blockage or faulty inversion valve preventing air from reaching the spring cavity Correct answer.
  4. A slack adjuster adjusted too tight

Explanation

Releasing the parking brake requires air to reach the spring cavity through the parking valve and, on some systems, an inversion valve. A blockage or failed valve leaves the spring applied despite normal gauge pressure.

Question 48Air Brake System Components and Operation

What is the purpose of the alcohol evaporator in an air brake system?

  1. It filters oil from the compressor discharge
  2. It increases the compressor's output pressure
  3. It introduces alcohol vapor into the air to lower the freezing point of moisture in the system Correct answer.
  4. It lubricates the brake chambers

Explanation

Alcohol vapor mixes with moisture in the air lines and lowers its freezing point, reducing the risk of ice blocking valves in cold weather. It is a cold-weather aid, not a substitute for draining tanks.

Question 49Air Brake System Components and Operation

Which statement accurately describes the relationship between the service brake and the spring brake in a typical combination chamber?

  1. The spring brake provides the service braking force during normal driving
  2. The spring brake must be released before the service brake can function
  3. They are separate systems sharing one pushrod, so either can apply the brake independently Correct answer.
  4. The service brake disables the spring brake whenever it is applied

Explanation

A combination chamber houses a service diaphragm and a spring brake section acting on the same pushrod. The service side applies with air during normal driving, while the spring side applies mechanically when air is exhausted.

Question 50Air Brake System Components and Operation

A driver performs a static leak test with the brakes fully applied and the engine off. What result indicates the system is holding pressure properly?

  1. The gauge drops steadily at more than 3 psi per minute
  2. The low-pressure warning activates during the test
  3. The gauge shows only a small drop within the allowed time specified for the vehicle Correct answer.
  4. The gauge rises as the brakes are held

Explanation

In a static leak test, pressure loss must stay within the manufacturer's allowable limit, typically a few psi over a specified period. A steady drop beyond that limit indicates a leak requiring repair.