FMVSS 135: Light Vehicle Brake Systems explained.

What FMVSS 135 says it is for

The eCFR heads this section "Standard No. 135; Light vehicle brake systems." Under 49 CFR part 571, the Federal Motor Vehicle Safety Standards are the numbered standards that set safety performance requirements for motor vehicles and equipment. The text below is quoted from 571.135 as current through October 29, 2026.

This standard specifies requirements for service brake and associated parking brake systems.

The purpose of this standard is to ensure safe braking performance under normal and emergency driving conditions.

What it applies to

The application section of the standard says:

This standard applies to passenger cars manufactured on or after September 1, 2000 and to multi-purpose passenger vehicles, trucks and buses with a gross vehicle weight rating (GVWR) of 3,500 kilograms (7,716 pounds) or less, manufactured on or after September 1, 2002. In addition, at the option of the manufacturer, passenger cars manufactured before September 1, 2000, and multi-purpose passenger vehicles, trucks and buses with a GVWR of 3,500 kilograms (7,716 pounds) or less, manufactured before September 1, 2002, may meet the requirements of this standard instead of Federal Motor Vehicle No. 105, Hydraulic Brake Systems.

Applicability is decided by the text of the standard as written, including any exclusions it lists, and by the date-specific rules in it. This page does not decide whether a particular vehicle or item is covered.

How the standard is organized

The eCFR text of 571.135 has these top-level sections:

• S1: Scope
• S2: Purpose
• S3: Application
• S4: Definitions
• S5: Equipment requirements
• S6: General test conditions
• S7: Road test procedures and performance requirements

In all, the text has 127 numbered headings. Use the finder above to search them; for example, a search for "test" lists the headings that mention tests.

Second-level headings at a glance

These are the numbered sub-sections one level below the top, in order (first 28 of 28):

• S5.1 Service brake system
• S5.2 Parking brake system
• S5.3 Controls
• S5.4 Reservoirs
• S5.5 Brake system warning indicator
• S5.6 Brake system integrity
• S6.1 Ambient conditions
• S6.2 Road test surface
• S6.3 Vehicle conditions
• S6.4 Instrumentation
• S6.5 Procedural conditions
• S7.1 Burnish
• S7.2 Wheel lockup sequence
• S7.3 ABS performance
• S7.4 Adhesion utilization (Torque Wheel Method)
• S7.5 Cold effectiveness
• S7.6 High speed effectiveness
• S7.7 Stops with Engine Off
• S7.8 Antilock functional failure
• S7.9 Variable brake proportioning system functional failure
• S7.10 Hydraulic circuit failure
• S7.11 Brake power unit or brake power assist unit inoperative (System depleted)
• S7.12 Parking brake
• S7.13 Heating Snubs
• S7.14 Hot performance
• S7.15 Brake cooling stops
• S7.16 Recovery performance
• S7.17 Final Inspection

Key requirements, quoted from the text

These are excerpts from the requirements sections of 571.135, in the order the standard presents them. Long paragraphs are shortened where marked with [...]; the eCFR has the complete text, tables and figures, which this page omits.

S5.1 Service brake system. Each vehicle shall be equipped with a service brake system acting on all wheels.

S5.1.1 Wear adjustment. Wear of the service brakes shall be compensated for by means of a system of automatic adjustment.

S5.1.2 Wear status. The wear condition of all service brakes shall be indicated by either: (a) Acoustic or optical devices warning the driver at his or her driving position when lining replacement is necessary, or (b) A means of visually checking the degree of brake lining wear, from the outside or underside of the vehicle, utilizing only the tools or equipment normally supplied with the vehicle. The removal of wheels is permitted for this purpose.

S5.1.3 Regenerative braking system. (a) For an EV equipped with RBS, the RBS is considered to be part of the service brake system if it is automatically activated by an application of the service brake control, if there is no means provided for the driver to disconnect or otherwise deactivate it, and if it is activated in all transmission positions, including neutral. (b) For an EV that is equipped with both ABS and RBS that is part of the service brake system, the ABS must control the RBS.

S5.2 Parking brake system. Each vehicle shall be equipped with a parking brake system of a friction type with solely mechanical means to retain engagement.

S5.3 Controls. S5.3.1. The service brakes shall be activated by means of a foot control. The control of the parking brake shall be independent of the service brake control, and may be either a hand or foot control. S5.3.2. For vehicles equipped with ABS, a control to manually disable the ABS, either fully or partially, is prohibited.

S6 General test conditions. Each vehicle must meet the performance requirements specified in S7 under the following test conditions and in accordance with the test procedures and test sequence specified. Where a range of conditions is specified, the vehicle must meet the requirements at all points within the range.

S6.1.1 Ambient temperature. The ambient temperature is any temperature between 0 °C (32 °F) and 40 °C (104 °F).

S6.1.2 Wind speed. The wind speed is not greater than 5 m/s (11.2 mph).

S6.2.1 Pavement friction. Unless otherwise specified, the road test surface produces a peak friction coefficient (PFC) of 1.02 when measured using an ASTM F2493 standard reference test tire, in accordance with ASTM E1337-19 (incorporated by reference, see § 571.5), at a speed of 64.4 km/h (40 mph), without water delivery.

S6.2.2 Gradient. Except for the parking brake gradient holding test, the test surface has no more than a 1% gradient in the direction of testing and no more than a 2% gradient perpendicular to the direction of testing.

S6.2.3 Lane width. Road tests are conducted on a test lane 3.5 m (11.5 ft) wide.

S7 Road test procedures and performance requirements. Each vehicle shall meet all the applicable requirements of this section, when tested according to the conditions and procedures set forth below and in S6, in the sequence specified in Table 1:

S7.1.1 General information. Any pretest instrumentation checks are conducted as part of the burnish procedure, including any necessary rechecks after instrumentation repair, replacement or adjustment. Instrumentation check test conditions must be in accordance with the burnish test procedure specified in S7.1.2 and S7.1.3.

S7.1.2 Vehicle conditions. (a) Vehicle load: GVWR only. (b) Transmission position: In gear.

S7.1.3 Test conditions and procedures. The road test surface conditions specified in S6.2 do not apply to the burnish procedure. (a) IBT: ≤100 °C (212 °F). (b) Test speed: 80 km/h (49.7 mph). (c) Pedal force: Adjust as necessary to maintain specified constant deceleration rate. (d) Deceleration rate: Maintain a constant deceleration rate of 3.0 m/s 2 (9.8 fps 2). (e) Wheel lockup: No lockup of any wheel allowed for longer than 0.1 seconds at speeds greater than 15 km/h (9.3 mph). (f) Number of runs: 200 stops. (g) Interval between runs: The interval from the start of one service brake application to the start of the next is either the time necessary to reduce the IBT to 100 °C (212 °F) or less, or the distance of 2 km (1.24 miles), whichever occurs first. [...]

S7.2.1 General information. (a) The purpose of this test is to ensure that lockup of both front wheels occurs either simultaneously with, or at a lower deceleration rate than, the lockup of both rear wheels, when tested on road surfaces affording adhesion such that wheel lockup of the first axle occurs at a braking ratio of between 0.15 and 0.80, inclusive. (b) This test is for vehicles without antilock brake systems. (c) This wheel lock sequence test is to be used as a screening test to evaluate a vehicle's axle lockup sequence and to determine whether the torque wheel test in S7.4 must be conducted. [...]

S7.2.2 Vehicle conditions. (a) Vehicle load: GVWR and LLVW. (b) Transmission position: In neutral.

Defined terms

The standard defines 24 terms in its definitions section; the first 12 are quoted here from the eCFR.

• Adhesion utilization curves means curves showing, for specified load conditions, the adhesion utilized by each axle of a vehicle plotted against the braking ratio of the vehicle.
• Antilock brake system or ABS means a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by:
• Backup system means a portion of a service brake system, such as a pump, that automatically supplies energy in the event of a primary brake power source failure.
• Brake factor means the slope of the linear least squares regression equation best representing the measured torque output of a brake as a function of the measured applied line pressure during a given brake application for which no wheel lockup occurs.
• Brake hold-off pressure means the maximum applied line pressure for which no brake torque is developed, as predicted by the pressure axis intercept of the linear least squares regression equation best representing the measured torque output of a brake as a function of the measured applied line pressure during a given brake application.
• Brake power assist unit means a device installed in a hydraulic brake system that reduces the amount of muscular force that a driver must apply to actuate the system, and that, if inoperative, does not prevent the driver from braking the vehicle by a continued application of muscular force on the service brake control.
• Brake power unit means a device installed in a brake system that provides the energy required to actuate the brakes, either directly or indirectly through an auxiliary device, with driver action consisting only of modulating the energy application level.
• Braking ratio means the deceleration of the vehicle divided by the gravitational acceleration constant.
• Electric vehicle or EV means a motor vehicle that is powered by an electric motor drawing current from rechargeable storage batteries, fuel cells, or other portable sources of electrical current, and which may include a non-electrical source of power designed to charge batteries and components thereof.
• Electrically-actuated service brakes means service brakes that utilize electrical energy to actuate the foundation brakes.
• Functional failure means a failure of a component (either electrical or mechanical in nature) which renders the system totally or partially inoperative yet the structural integrity of the system is maintained.
• Hydraulic brake system means a system that uses hydraulic fluid as a medium for transmitting force from a service brake control to the service brake and that may incorporate a brake power assist unit, or a brake power unit.

Limits of this page

This page quotes the text of 49 CFR 571.135 as published in the eCFR, current through October 29, 2026. It omits tables, figures, cross-referenced test procedures in other parts, and the preambles and rulemaking history that explain the rule. It does not tell you whether a given vehicle, part or product complies, how to run a test, or what a manufacturer must certify. Compliance questions go to the manufacturer's engineers, qualified counsel or NHTSA. The eCFR is an editorial compilation, not the official legal edition of the Federal Register.

Sources

Sources opened and read November 2, 2026.

• eCFR: 49 CFR 571.135, Standard No. 135; Light vehicle brake systems. (current through October 29, 2026) (read November 2, 2026)
• eCFR: 49 CFR part 571, Federal Motor Vehicle Safety Standards (current through October 29, 2026) (read November 2, 2026)