FMVSS 141: Minimum Sound Requirements explained.

What FMVSS 141 says it is for

The eCFR heads this section "Standard No. 141; Minimum Sound Requirements for Hybrid and Electric Vehicles." 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 571.141 as current through October 29, 2026.

This standard establishes performance requirements for pedestrian alert sounds for motor vehicles.

The purpose of this standard is to reduce the number of injuries that result from electric and hybrid vehicle crashes with pedestrians by providing a sound level and sound characteristics necessary for these vehicles to be detected and recognized by pedestrians.

What it applies to

The application section of the standard says:

This standard applies to— (a) Electric vehicles with a gross vehicle weight rating (GVWR) of 4,536 Kg or less that are passenger cars, multipurpose passenger vehicles, trucks, or buses; (b) Hybrid vehicles with a gross vehicle weight rating (GVWR) of 4,536 Kg or less that are passenger cars, multi-purpose passenger vehicles, trucks, or buses; and (c) Electric vehicles and hybrid vehicles that are low speed vehicles. S4. Definitions. Band or one-third octave band means one of thirteen one-third octave bands having nominal center frequencies ranging from 315 to 5000Hz. These are Bands 25 through 37 as defined in Table A1, Mid-band Frequencies for One-Third-Octave-Band and Octave-Band Filters in the Audio Range, of ANSI S1.11-2004: “Specification for Octave-Band and Fractional-Octave-Band Analog and Digital Filters” (incorporated by reference, see § 571.5). Band sum means the combination of Sound Pressure Levels (SPLs) from selected bands that produce an SPL representing the sound in all of these bands. Band sum is calculated with the following equation: Electric vehicle means a motor vehicle with an electric motor as its sole means of propulsion. Front plane of the vehicle means a vertical plane tangent to the leading edge of the vehicle during forward operation. [...]

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 571.141 has these top-level sections:

• S1: Scope
• S2: Purpose
• S3: Application
• S5: Requirements
• S6: Test Conditions
• S7: Test Procedure
• S8: Prohibition on altering the sound of a vehicle subject to this standard
• S9: Phase-in schedule

In all, the text has 47 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 19 of 19):

• S5.1 Performance requirements for four-band alert sounds
• S5.2 Performance requirements for two-band alert sounds
• S5.4 Relative volume change to signify acceleration and deceleration
• S5.5 Sameness requirement
• S6.1 Weather conditions
• S6.2 Test surface
• S6.3 Instrumentation
• S6.4 Test site
• S6.5 Test set up for directivity measurement
• S6.6 Vehicle condition
• S6.7 Ambient correction
• S7.1 Stationary vehicle in forward gear
• S7.2 Stationary vehicle in reverse gear
• S7.3 Constant speed pass-by tests at speeds greater than 0 km/h but less than 20 km/h
• S7.4 Pass-by tests at speeds greater than or equal to 20 km/h and less than 30 km/h
• S7.5 Pass-by tests at 30 km/h
• S7.6 Relative volume change
• S9.1 Hybrid and Electric Vehicles manufactured on or after March 1, 2020, and before February 28, 2021
• S9.2 Hybrid and Electric Vehicles manufactured on or after March 1, 2021

Key requirements, quoted from the text

These are excerpts from the requirements sections of 571.141, 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 Requirements. Subject to the phase-in set forth in S9 of this standard, each hybrid and electric vehicle must meet the requirements specified in either S5.1 or S5.2. subject to the requirements in S5.3. Each vehicle must also meet the requirements in S5.4 and S5.5.

S5.1.1 Stationary. When stationary the vehicle must satisfy S5.1.1.1 and S5.1.1.2 whenever the vehicle's propulsion system is activated and: (i) In the case of a vehicle with an automatic transmission, the vehicle's gear selector is in Neutral or any gear position other than Park that provides forward vehicle propulsion; (iii) in the case of a vehicle with a manual transmission, the vehicle's parking brake is released and the gear selector is not in Reverse. S5.1.1.1 For detection, the vehicle must emit a sound having at least the A-weighted sound pressure level according to Table 1 in each of four non-adjacent bands spanning no fewer than 9 of the 13 bands from 315 to 5000 Hz. [...]

S5.1.2 Reverse. For vehicles capable of rearward self-propulsion, whenever the vehicle's gear selector is in the Reverse position, the vehicle must emit a sound having at least the A-weighted sound pressure level according to Table 2 in each of four non-adjacent bands spanning no fewer than 9 of the 13 bands from 315 to 5000Hz.

S5.1.3 Constant pass-by speeds greater than 0 km/h but less than 20 km/h. When at a constant speed greater than 0 km/h but less than 20 km/h the vehicle must emit a sound having at least the A-weighted sound pressure level according to Table 1 or Table 3 as applicable based upon vehicle test speed in each of four non-adjacent bands spanning no fewer than 9 of the 13 bands from 315 to 5000 Hz.

S5.1.4 Constant pass-by speeds greater than or equal to 20km/h but less than 30 km/h. When at a constant speed equal to or greater than 20 km/h but less than 30 km/h the vehicle must emit a sound having at least the A-weighted sound pressure level according to Table 4 in each of four non-adjacent bands spanning no fewer than 9 of the 13 bands from 315 to 5000 Hz.

S5.1.5 Constant 30km/h pass-by. When at a constant speed of 30-32 km/h the vehicle must emit a sound having at least the A-weighted sound pressure level according to Table 5 in each of four non-adjacent bands spanning no fewer than 9 of the 13 bands from 315 to 5000 Hz.

S6.1 Weather conditions. The ambient conditions specified by this section will be met at all times during the tests described in S7. Conditions will be measured with the accuracy required in S6.3.3 at the microphone height specified in S6.4 ±0.02 m.

S6.1.4 Background noise level. The background noise level will be measured and reported as specified in S6.7, Ambient correction.

S6.2 Test surface. Test surface will meet the requirements of ISO 10844:1994, ISO 10844:2011, or ISO 10844:2014 (incorporated by reference, see § 571.5).

S6.3.1 Acoustical measurement. Instruments for acoustical measurement will meet the requirements of S5.1 of SAE J2889-1 (incorporated by reference, see § 571.5).

S6.3.2 Vehicle speed measurement. Instruments used to measure vehicle speed during the constant speed pass-by tests in S7 of this standard will be capable of either continuous measurement of speed within ±0.5 km/h over the entire measurement zone specified in S6.4 or independent measurements of speed within ±0.2 km/h at the beginning and end of the measurement zone specified in S6.4.

S6.3.3 Meteorological instrumentation. Instruments used to measure ambient conditions at the test site will meet the requirements of S5.3 of SAE J2889-1 (incorporated by reference, see § 571.5).

S7.1.1 Execute stationary tests and collect acoustic sound files. (a) Position the vehicle with the front plane at the line PP', the vehicle centerline on the line CC' and the starting system deactivated. For vehicle equipped with a Park position, place the vehicle's gear selector in “Park” and engage the parking brake. For vehicles not equipped with a Park position, place the vehicle's gear selector in “Neutral” and engage the parking brake. Activate the starting system to energize the vehicle's propulsion system. (b) For vehicles equipped with a Park position for the gear selector, after activating the starting system to energize the vehicle's propulsion system, apply and maintain a full application of the service brake, disengage the vehicle parking brake and then place the vehicle's gear selector in “Drive,” or any forward gear. [...]

S7.1.2 Eliminate invalid tests. (a) Determine validity of sound files collected during S7.1.1 tests. Measurements that contain any distinct, transient, loud sounds (e.g., chirping birds, overhead planes, trains, car doors being slammed, etc.) are considered invalid. Measurements that contain sounds emitted by any vehicle system that is automatically activated and constantly engaged during the entire 10 second performance test are considered valid. Measurements that contain sound emitted by any vehicle system that is automatically activated and intermittently engaged at any time during the stationary performance test, are considered invalid. [...]

S7.1.3 Identify first four valid tests within 2dBA. (a) For each valid test sound file identified in S7.1.2, determine a maximum overall SPL value, in decibels. Each SPL value will be reported to the nearest tenth of a decibel. (b) Compare the first four left-side SPL values from S7.1.3(a) of this paragraph, and determine the range by taking the difference between the largest and smallest of the four values. In the same manner, determine the range of SPL values for the first four right-side and the first four front-center sound files. If the range for the left side, right side, and front-center are all less than or equal to 2.0 dB, then the twelve sound files associated with the first four valid tests will be used for the one-third octave band evaluations in S7.1.5. and S7.1.6. [...]

S7.1.4 Compare the average overall SPL for the left and right side of the test vehicle to determine which is lower. (a) Document the maximum overall SPL values in each of the eight acoustic data files (four left side files and four right side files) identified in S7.1.3. (b) Correct each of the eight SPL values from S7.1.4(a) according to S6.7 using the ambient sound level recorded during the test. The results will be reported to the nearest tenth of a decibel. (c) Calculate a left-side average and a right-side average from the ambient-corrected overall SPL values from S71.4(b), and determine the lower of the two sides. The result will be reported to the nearest tenth of a decibel. (d) If the left-side value from S7.1.4(c) is the lower one, then the left side acoustic data will be further evaluated for compliance at the one-third octave band levels in accordance with S7.1.5. [...]

S7.2 Stationary vehicle in reverse gear. Test the vehicle per S7.1.1 through S7.1.5 except that the rear plane of the vehicle is placed on the PP' line, no center microphone is used, and the vehicle's transmission gear selector is placed in the `Reverse' position. The minimum sound level requirements for the Reverse test condition are contained in S5.1.2, Table 2, for four-band compliance and in S5.2, Table 6, for two-band compliance.

S7.3.1 Execute pass-by tests at 11km/h (±1 km/h) and collect acoustic sound files. (a) For each test, measure the sound emitted by the test vehicle while at a constant speed of 11km/h (± 1km/h) throughout the measurement zone specified in S6.4 between lines AA' and PP'. Execute multiple test runs at 11km/h (±1km/h) to acquire at least four valid tests within 2dBA in accordance with S7.3.2 and S7.3.3. (b) During each test, record a left (driver's side) and a right (passenger side) acoustic sound file.

S8 Prohibition on altering the sound of a vehicle subject to this standard. No entity subject to the authority of the National Highway Traffic Safety Administration may: (a) Disable, alter, replace, or modify any element of a vehicle installed as original equipment for purposes of complying with this Standard, except in connection with a repair of a vehicle malfunction or to remedy a defect or non-compliance; or (b) Provide any person with any mechanism, equipment, process, or device intended to disable, alter, replace, or modify the sound emitting capability of a vehicle subject to this standard, except in connection with a repair of vehicle malfunction or to remedy a defect or non-compliance.

S9.1 Hybrid and Electric Vehicles manufactured on or after March 1, 2020, and before February 28, 2021. For hybrid and electric vehicles to which this standard applies manufactured on and after March 1, 2020, and before March 1, 2021, except vehicles produced by small volume manufacturers, the quantity of hybrid and electric vehicles complying with this safety standard shall be not less than 50 percent of one or both of the following: (a) A manufacturer's average annual production of hybrid and electric vehicles on and after September 1, 2016, and before September 1, 2019; (b) A manufacturer's total production of hybrid and electric vehicles on and after March 1, 2020, and before March 1, 2021.

S9.2 Hybrid and Electric Vehicles manufactured on or after March 1, 2021. All hybrid and electric vehicles to which this standard applies manufactured on or after March 1, 2021, shall comply with this safety standard.

Limits of this page

This page quotes the text of 49 CFR 571.141 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 571.141, Standard No. 141; Minimum Sound Requirements for Hybrid and Electric Vehicles. (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)