100+ Free ASE T4 Brakes (Medium/Heavy Truck) Practice Questions

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What is the purpose of the modulated (graduated) spring brake / inversion valve function on some trucks?

To increase governor cut-out

To allow controlled spring-brake application to help stop the truck if service air is lost, rather than an abrupt full lock

To drain the wet tank

To charge the trailer

to track

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Key Facts: ASE T4 Brakes (Medium/Heavy Truck) Exam

Total Questions (50 scored)

ASE Medium/Heavy Truck T4 test page

75 min

Time Limit

ASE T4 test information

~$59

ASE Registration Fee

ASE test registration

Criterion-referenced

Scoring Method

ASE scoring policy

64 / 22 / 14

Air / Hydraulic / ABS-ATC-ESC Split

ASE T4 content outline

Prometric

Test Provider

ASE testing logistics

ASE lists the Medium/Heavy Truck Brakes (T4) test as a 60-question test (50 scored plus 10 unscored research questions) with a 75-minute time limit, delivered by Prometric. Scoring is criterion-referenced, meaning a passing score is set by ASE against a defined competency standard rather than a fixed percentage. The official content split is Air Brakes Diagnosis & Repair (64 questions, including air supply and service systems, mechanical/foundation and wheel-end, and parking brakes), Hydraulic Brakes Diagnosis & Repair (22 questions), and ABS, ATC, Electronic Stability Control & Collision Warning/Avoidance Systems (14 questions). Certification requires two years of relevant work experience (training can substitute for up to one year), and T4 counts toward the Master Medium/Heavy Truck credential. This free practice bank provides 100 selected-response items across all official content areas.

Sample ASE T4 Brakes (Medium/Heavy Truck) Practice Questions

Try these sample questions to test your ASE T4 Brakes (Medium/Heavy Truck) exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1On a typical heavy-truck air brake system, what is the primary job of the air compressor governor?

A.It meters air to the front and rear circuits in a fixed ratio

B.It limits the maximum service brake application pressure delivered to the brake chambers

C.It cycles the compressor between loaded (building air) and unloaded modes to maintain reservoir pressure within a set range

D.It controls the spring brake hold-off pressure

Explanation: The governor senses reservoir pressure and signals the compressor to stop pumping (unload) at the cut-out pressure and resume pumping (load) at the cut-in pressure, keeping system pressure in the normal operating band. Typical cut-out is about 120-135 psi and cut-in about 100-110 psi.

2Typical air brake governor cut-out (compressor unload) pressure on a heavy truck is closest to which range?

A.160 to 175 psi

B.60 to 75 psi

C.85 to 95 psi

D.120 to 135 psi

Explanation: Most heavy-truck systems are set to cut out (stop building air) around 120-135 psi and cut back in around 100-110 psi, giving roughly a 20-25 psi differential. This keeps reservoir pressure well above the level needed for full braking.

3The first (supply) reservoir downstream of the compressor on a heavy truck is commonly called the wet tank. Why is it called wet?

A.It is filled with brake fluid to lubricate valves

B.It collects condensed water and oil that fall out of the compressed air before it reaches the service tanks

C.It is the only tank pressurized when the engine is off

D.It supplies windshield washer fluid to the system

Explanation: As hot compressed air cools in the first reservoir, moisture and compressor oil condense and collect there, so it is called the wet (supply) tank. Draining it regularly, or using an air dryer, keeps water and oil out of the primary and secondary service tanks.

4An air dryer with a desiccant cartridge is installed on a tractor. What is its main purpose?

A.To remove moisture and oil from the compressed air before it enters the reservoirs

B.To regulate brake application pressure

C.To warm the air to prevent valve freeze-up only

D.To increase compressor output pressure

Explanation: The air dryer passes compressed air through a desiccant bed that adsorbs water vapor and traps oil, sending dry, clean air to the reservoirs. This reduces corrosion, valve freeze-up, and contamination of downstream valves and chambers.

5A technician finds excessive oil being expelled from the air dryer purge valve and oil contamination in the reservoirs. Which is the MOST likely root cause?

A.A leaking front brake chamber diaphragm

B.An over-adjusted slack adjuster

C.A worn or failing air compressor passing oil into the discharge air

D.A stuck-open quick-release valve

Explanation: Persistent oil downstream of the dryer usually means the compressor is pumping oil past worn rings or through a failing unloader, overwhelming the dryer. The dryer can only handle limited oil, so the compressor should be inspected and likely rebuilt or replaced.

6FMVSS 121 sets air system performance requirements for trucks. Which statement best reflects an FMVSS 121 air-buildup requirement?

A.Spring brakes must release at 20 psi

B.The compressor must cut out at exactly 150 psi

C.Service brakes must hold pressure for 24 hours

D.The system must build from 50 to 90 psi within a specified time at a given engine speed

Explanation: FMVSS 121 specifies a maximum air pressure build-up time, commonly stated as building from 50 psi to 90 psi within about 25 seconds at a defined engine speed for a fully equipped vehicle. Slow build-up indicates a weak compressor, restriction, or leakage.

7A heavy truck takes far too long to build air pressure from 85 to 100 psi during a buildup test. Technician A says a restricted air dryer or supply line could cause slow buildup. Technician B says worn compressor rings or a leaking discharge valve could cause it. Who is correct?

A.Technician A only

B.Technician B only

C.Both Technician A and Technician B

D.Neither technician

Explanation: Slow air build-up has both supply-restriction causes (clogged dryer, kinked or restricted lines, sticking governor) and compressor causes (worn rings, leaking discharge or unloader valves, slipping drive). Both technicians describe valid contributors, so both are correct.

8At what reservoir pressure must the air brake low-pressure warning device activate, per common FMVSS 121 requirements?

A.Only after the pressure reaches zero

B.At 120 psi cut-out pressure

C.At or above 60 psi

D.At exactly 100 psi

Explanation: FMVSS 121 requires the low air pressure warning (light and audible buzzer) to activate at or above 60 psi so the driver is alerted while there is still enough air to stop the vehicle. Many systems trigger the warning around 60-70 psi.

9What is the function of the safety (pressure relief) valve usually mounted on the supply (wet) reservoir?

A.To release air if system pressure rises too high due to a failed governor or compressor unloader

B.To bleed condensation automatically every few minutes

C.To prevent the trailer from charging too fast

D.To hold off the spring brakes

Explanation: The safety relief valve protects the system if the governor or compressor unloader fails and pressure climbs above a safe level (commonly set around 150 psi). It vents excess air to prevent reservoir or component damage.

10A truck has a single-check valve between the supply reservoir and the primary reservoir. What does this check valve accomplish?

A.It allows air to flow into the primary tank but prevents back-flow if upstream pressure is lost

B.It proportions braking between axles

C.It limits compressor output

D.It exhausts the brake chambers on release

Explanation: A one-way check valve lets air charge the downstream reservoir but blocks reverse flow. This isolates the primary reservoir so a leak or rupture upstream does not drain the protected tank, preserving braking capability.

About the ASE T4 Brakes (Medium/Heavy Truck) Exam

ASE T4 — Brakes (Medium/Heavy Truck) certifies technicians who diagnose and repair brake systems on medium- and heavy-duty trucks. The test covers air brake supply and service systems, mechanical foundation and wheel-end brakes, parking/spring brakes, hydraulic brakes, and ABS/ATC/electronic stability control with collision warning and avoidance systems.

Assessment

50 scored multiple-choice (60 total incl. 10 unscored) (official ASE); this practice bank is 100 selected-response items

Time Limit

75 minutes

Passing Score

Criterion-referenced (set by ASE)

Exam Fee

~$59 (ASE registration) (ASE (National Institute for Automotive Service Excellence))

ASE T4 Brakes (Medium/Heavy Truck) Exam Content Outline

64 questions (~64%)

Air Brakes Diagnosis & Repair

The dominant area. Air Supply & Service Systems (~30 questions): air compressor and governor cut-in/cut-out, wet and dry reservoirs, air dryer, FMVSS 121 air build-up and leakage limits, low-air warning, safety valve, primary/secondary dual circuits, treadle, relay, quick-release, ratio, double-check, and tractor protection valves. Mechanical/Foundation & Wheel-End (~26 questions): S-cam versus air disc foundation brakes, manual and automatic slack adjusters, brake chambers, pushrod stroke and readjustment limits, drums, linings and friction codes, wheel hubs, bearings, and seals. Parking Brakes (~8 questions): spring brake chambers, hold-off pressure, caging safety, and anti-compounding.

22 questions (~22%)

Hydraulic Brakes Diagnosis & Repair

Tandem master cylinders and split circuits, hydro-boost and vacuum power assist, accumulators, air-over-hydraulic systems, brake fluid types and contamination, system bleeding, calipers, rotors, drums and wheel cylinders, residual/metering/proportioning and height-sensing load-sensing valves, and pressure-differential warning-lamp diagnosis on medium trucks.

14 questions (~14%)

ABS, ATC, Electronic Stability Control & Collision Warning/Avoidance Systems Diagnosis & Repair

Antilock braking operation, variable-reluctance wheel speed sensors and tone rings, modulator (pressure control) valves, ABS warning lamps and stored codes, automatic traction control, electronic stability control, trailer ABS, correct tire size and rolling-radius matching, and forward collision warning and mitigation systems.

How to Pass the ASE T4 Brakes (Medium/Heavy Truck) Exam

What You Need to Know

Passing score: Criterion-referenced (set by ASE)
Assessment: 50 scored multiple-choice (60 total incl. 10 unscored) (official ASE); this practice bank is 100 selected-response items
Time limit: 75 minutes
Exam fee: ~$59 (ASE registration)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ASE T4 Brakes (Medium/Heavy Truck) Study Tips from Top Performers

1Weight study time by the blueprint: Air Brakes Diagnosis & Repair is 64 of 100 questions, so air supply, service valves, foundation brakes, and spring brakes deserve the most prep.

2Know the numbers cold: governor cut-out (~120-135 psi), low-air warning (at or above 60 psi), FMVSS 121 build-up (50 to 90 psi within about 25 seconds), and chamber pushrod readjustment limits by type.

3Practice systematic leak and balance diagnosis: applied versus static leakage limits, soap-bubble isolation, pushrod stroke measurement at 90-100 psi, and side-to-side brake balance.

4Respect spring brake safety: always cage the power spring or fully depressurize before disassembling a spring brake chamber, and never road-operate with springs caged.

5Expect Technician A / Technician B questions; evaluate each statement independently before choosing both, one, or neither.

6Review medium/heavy-truck specifics such as S-cam versus air disc foundation brakes, air-over-hydraulic systems, and ABS/ATC/ESC tone-ring and tire-matching diagnosis.

Frequently Asked Questions

How many questions are on the ASE T4 Brakes test?

ASE lists the Medium/Heavy Truck Brakes (T4) test with 60 total questions, of which 50 are scored and 10 are unscored research questions that do not count toward your result. This free practice bank provides 100 selected-response items so you can drill every content area more deeply than the live test length.

How much time do I get and how is ASE T4 scored?

ASE allots 75 minutes for the T4 test, delivered through Prometric. ASE scoring is criterion-referenced, which means a passing result is determined against a defined competency standard set by ASE rather than a fixed percentage or a curve against other test-takers.

What does ASE T4 cost and what are the eligibility requirements?

ASE registration for a single specialty test such as T4 is approximately $59; confirm the current amount when you register. To become certified you also need two years of relevant hands-on work experience, although an approved training program can substitute for up to one of those two years.

What content area should I study most for ASE T4?

Air Brakes Diagnosis & Repair is by far the largest area at 64 of 100 questions, split across air supply and service systems, mechanical foundation and wheel-end work, and parking/spring brakes. Hydraulic Brakes (22) and ABS/ATC/ESC with collision systems (14) follow, so weight most of your prep toward air-brake diagnosis and component operation.

Is ASE T4 required for the Master Medium/Heavy Truck Technician certification?

Yes, T4 Brakes is one of the T-series tests used toward the Master Medium/Heavy Truck Technician credential. It is still registered for and taken individually, and many fleet technicians prioritize T4 because brake compliance and FMVSS 121 performance are central to commercial vehicle safety.

Are there any 2026 changes to the ASE T4 test?

As of 2026 ASE continues to list the Medium/Heavy Truck T4 test under the standard T-series structure with a 75-minute limit, Prometric delivery, and criterion-referenced scoring. Always verify the live ASE test page and your myASE account for the current registration fee, scheduling, and any content-area updates before you test.

100+ Free ASE T4 Brakes (Medium/Heavy Truck) Practice Questions

ASE T4 Brakes (Medium/Heavy Truck)

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