FMVSS 126: Electronic Stability Control Systems explained.

What FMVSS 126 says it is for

The eCFR heads this section "Standard No. 126; Electronic stability control systems for light 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 571.126 as current through October 29, 2026.

This standard establishes performance and equipment requirements for electronic stability control (ESC) systems.

The purpose of this standard is to reduce the number of deaths and injuries that result from crashes in which the driver loses directional control of the vehicle, including those resulting in vehicle rollover.

What it applies to

The application section of the standard says:

This standard applies to passenger cars, multipurpose passenger vehicles, trucks, and buses with a gross vehicle weight rating of 4,536 kilograms (10,000 pounds) or less, according to the phase-in schedule specified in S8 of this standard.

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 571.126 has these top-level sections:

• S1: Scope
• S2: Purpose
• S3: Application
• S4: Definitions
• S5: Requirements
• S6: Test Conditions
• S7: Test Procedure
• S8: 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 25 of 25):

• S5.1 Required Equipment
• S5.2 Performance Requirements
• S5.3 ESC Malfunction
• S5.4 ESC Off and Other System Controls
• S5.5 ESC Off Telltale
• S5.6 ESC System Technical Documentation
• S6.1 Ambient conditions
• S6.2 Road test surface
• S6.3 Vehicle conditions
• S7.2 Telltale bulb check
• S7.3 “ESC Off” control check
• S7.4 Brake Conditioning
• S7.5 Tire Conditioning
• S7.6 Slowly Increasing Steer Test
• S7.9 Sine with Dwell Test of Oversteer Intervention and Responsiveness
• S7.10 ESC Malfunction Detection
• S7.11 Post Data Processing—Calculations for Performance Metrics
• S8.1 Vehicles manufactured on or after September 1, 2008, and before September 1, 2009
• S8.2 Vehicles manufactured on or after September 1, 2009, and before September 1, 2010
• S8.3 Vehicles manufactured on or after September 1, 2010, and before September 1, 2011
• S8.4 Vehicles manufactured on or after September 1, 2011
• S8.5 Calculation of complying vehicles
• S8.6 Vehicles produced by more than one manufacturer
• S8.7 Small volume manufacturers
• S8.8 Final-stage manufacturers and alterers

Key requirements, quoted from the text

These are excerpts from the requirements sections of 571.126, 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 S8, each vehicle must be equipped with an ESC system that meets the requirements specified in S5 under the test conditions specified in S6 and the test procedures specified in S7 of this standard.

S5.1 Required Equipment. Vehicles to which this standard applies must be equipped with an electronic stability control system that: S5.1.1 Is capable of applying brake torques individually to all four wheels and has a control algorithm that utilizes this capability. S5.1.2 Is operational during all phases of driving including acceleration, coasting, and deceleration (including braking), except when the driver has disabled ESC, the vehicle speed is below 20 km/h (12.4 mph), the vehicle is being driven in reverse, or during system initialization

S5.2 Performance Requirements. During each test performed under the test conditions of S6 and the test procedure of S7.9, the vehicle with the ESC system engaged must satisfy the stability criteria of S5.2.1 and S5.2.2, and it must satisfy the responsiveness criterion of S5.2.3 during each of those tests conducted with a commanded steering wheel angle of 5A or greater, where A is the steering wheel angle computed in S7.6.1. S5.2.1 The yaw rate measured one second after completion of the sine with dwell steering input (time T0 + 1 in Figure 1) must not exceed 35 percent of the first peak value of yaw rate recorded after the steering wheel angle changes sign (between first and second peaks) (åPeak in Figure 1) during the same test run, and S5.2.2 The yaw rate measured 1.75 seconds after completion of the sine with dwell [...]

S5.3 ESC Malfunction. The vehicle must be equipped with a telltale that provides a warning to the driver of the occurrence of one or more malfunctions that affect the generation or transmission of control or response signals in the vehicle's electronic stability control system. When tested according to S7.10, the ESC malfunction telltale: S5.3.1 As of September 1, 2011, must be mounted inside the occupant compartment in front of and in clear view of the driver; S5.3.2 As of September 1, 2011, must be identified by the symbol shown for “ESC Malfunction Telltale” or the specified words or abbreviations listed in Table 1 of Standard No. 101 (49 CFR 571.101); [...]

S5.3.6 The requirement S5.3.4 does not apply to telltales shown in a common space. S5.3.7 The ESC malfunction telltale must extinguish at the next ignition cycle after the malfunction has been corrected.

S5.3.8 The manufacturer may use the ESC malfunction telltale in a flashing mode to indicate ESC operation. S5.3.9 Prior to September 1, 2011, a disconnection of the power to the ESC electronic control unit may be indicated by the ABS malfunction telltale instead of the ESC malfunction telltale. S5.3.10 Manufacturers may use the ESC malfunction telltale in a steady-burning mode to indicate malfunctions of ESC-related systems and functions including traction control, trailer stability assist, corner brake control, and other similar functions that use throttle and/or individual wheel torque control to operate and share common components with the ESC system, and may use the ESC malfunction telltale in a flashing mode to indicate operation of these ESC-related systems.

S6.1.1 The ambient temperature is between 7 °C (45 °F) and 40 °C (104 °F). S6.1.2 The maximum wind speed is no greater than 10 m/s (22 mph) for passenger cars and 5 m/s (11 mph) for multipurpose passenger vehicles, trucks and buses.

S6.2 Road test surface. S6.2.1 The tests are conducted on a dry, uniform, solid-paved surface. Surfaces with irregularities and undulations, such as dips and large cracks, are unsuitable. S6.2.2 The road test surface must produce 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.

S6.3 Vehicle conditions. S6.3.1 The ESC system is enabled for all testing, except when it is turned off directly or by simulating a malfunction in accordance with S7.3 and S7.10, respectively. The ESC system shall be initialized as follows: Place the vehicle in a forward gear and obtain a vehicle speed of 48 ±8 km/h (30 ±5 mph). Drive the vehicle for at least two minutes including at least one left and one right turning maneuver and at least one application of the service brake.

S6.3.2 Test Weight. The vehicle is loaded with the fuel tank filled to at least 75 percent of capacity, and total interior load of 168 kg (370 lbs) comprised of the test driver, approximately 59 kg (130 lbs) of test equipment (automated steering machine, data acquisition system and the power supply for the steering machine), and ballast as required by differences in the weight of test drivers and test equipment. Where required, ballast shall be placed on the floor behind the passenger front seat or if necessary in the front passenger foot well area. All ballast shall be secured in a way that prevents it from becoming dislodged during test conduct.

S6.3.3 Tires. The vehicle is tested with the tires installed on the vehicle at time of initial vehicle sale. The tires are inflated to the vehicle manufacturer's recommended cold tire inflation pressure(s) specified on the vehicle's placard or the tire inflation pressure label. Tubes may be installed to prevent tire de-beading.

S6.3.4 Outriggers. Outriggers are used for testing trucks, multipurpose passenger vehicles, and buses. Vehicles with a baseline weight less than 1,588 kg (3,500 lbs) are equipped with “light” outriggers. Vehicles with a baseline weight equal to or greater than 1,588 kg (3,500 lbs) and less than 2,722 kg (6,000 lbs) are equipped with “standard” outriggers. Vehicles with a baseline weight equal to or greater than 2,722 kg (6,000 lbs) are equipped with “heavy” outriggers. A vehicle's baseline weight is the weight of the vehicle delivered from the dealer, fully fueled, with a 73 kg (160 lb) driver. Light outriggers are designed with a maximum weight of 27 kg (59.5 lb) and a maximum roll moment of inertia of 27 kg-m 2 (19.9 ft-lb-sec 2). [...]

S7 Test Procedure. S7.1 Inflate the vehicles' tires to the cold tire inflation pressure(s) provided on the vehicle's placard or the tire inflation pressure label.

S7.2 Telltale bulb check. With the vehicle stationary and the ignition locking system in the “Lock” or “Off” position, activate the ignition locking system to the “On” (“Run”) position or, where applicable, the appropriate position for the lamp check. The ESC malfunction telltale must be activated as a check of lamp function, as specified in S5.3.4, and if equipped, the “ESC Off” telltale must also be activated as a check of lamp function, as specified in S5.5.6. The telltale bulb check is not required for a telltale shown in a common space as specified in S5.3.6 and S5.5.8.

S7.3 “ESC Off” control check. For vehicles equipped with an “ESC Off” control, with the vehicle stationary and the ignition locking system in the “Lock” or “Off” position, activate the ignition locking system to the “On” (“Run”) position. Activate the “ESC Off” control and verify that the “ESC Off” telltale is illuminated, as specified in S5.5.4. Turn the ignition locking system to the “Lock” or “Off” position. Again, activate the ignition locking system to the “On” (“Run”) position and verify that the “ESC Off” telltale has extinguished indicating that the ESC system has been reactivated as specified in S5.4.1.

S7.4 Brake Conditioning. Condition the vehicle brakes as follows: S7.4.1 Ten stops are performed from a speed of 56 km/h (35 mph), with an average deceleration of approximately 0.5 g. S7.4.2 Immediately following the series of 56 km/h (35 mph) stops, three additional stops are performed from 72 km/h (45 mph). S7.4.3 When executing the stops in S7.4.2, sufficient force is applied to the brake pedal to activate the vehicle's antilock brake system (ABS) for a majority of each braking event. S7.4.4 Following completion of the final stop in S7.4.2, the vehicle is driven at a speed of 72 km/h (45 mph) for five minutes to cool the brakes.

S7.5 Tire Conditioning. Condition the tires using the following procedure to wear away mold sheen and achieve operating temperature immediately before beginning the test runs of S7.6 and S7.9. S7.5.1 The test vehicle is driven around a circle 30 meters (100 feet) in diameter at a speed that produces a lateral acceleration of approximately 0.5 to 0.6 g for three clockwise laps followed by three counterclockwise laps. S7.5.2 Using a sinusoidal steering pattern at a frequency of 1 Hz, a peak steering wheel angle amplitude corresponding to a peak lateral acceleration of 0.5-0.6 g, and a vehicle speed of 56 km/h (35 mph), the vehicle is driven through four passes performing 10 cycles of sinusoidal steering during each pass. [...]

S7.6 Slowly Increasing Steer Test. The vehicle is subjected to two series of runs of the Slowly Increasing Steer Test using a constant vehicle speed of 80 ±2 km/h (50 ±1 mph) and a steering pattern that increases by 13.5 degrees per second until a lateral acceleration of approximately 0.5 g is obtained. Three repetitions are performed for each test series. One series uses counterclockwise steering, and the other series uses clockwise steering. The maximum time permitted between each test run is five minutes. S7.6.1 From the Slowly Increasing Steer tests, the quantity “A” is determined. “A” is the steering wheel angle in degrees that produces a steady state lateral acceleration (corrected using the methods specified in S7.11.3) of 0.3 g for the test vehicle. [...]

S8.1 Vehicles manufactured on or after September 1, 2008, and before September 1, 2009. For vehicles manufactured on or after September 1, 2008, and before September 1, 2009, the number of vehicles complying with this standard must not be less than 55 percent of: (a) The manufacturer's average annual production of vehicles manufactured on or after September 1, 2005, and before September 1, 2008; or (b) The manufacturer's production on or after September 1, 2008, and before September 1, 2009.

S8.2 Vehicles manufactured on or after September 1, 2009, and before September 1, 2010. For vehicles manufactured on or after September 1, 2009, and before September 1, 2010, the number of vehicles complying with this standard must not be less than 75 percent of: (a) The manufacturer's average annual production of vehicles manufactured on or after September 1, 2006, and before September 1, 2009; or (b) The manufacturer's production on or after September 1, 2009, and before September 1, 2010.

S8.3 Vehicles manufactured on or after September 1, 2010, and before September 1, 2011. For vehicles manufactured on or after September 1, 2010, and before September 1, 2011, the number of vehicles complying with this standard must not be less than 95 percent of: (a) The manufacturer's average annual production of vehicles manufactured on or after September 1, 2007, and before September 1, 2010; or (b) The manufacturer's production on or after September 1, 2010, and before September 1, 2011.

S8.4 Vehicles manufactured on or after September 1, 2011. All vehicles manufactured on or after September 1, 2011 must comply with this standard.

S8.5 Calculation of complying vehicles. (a) For purposes of complying with S8.1, a manufacturer may count a vehicle if it is certified as complying with this standard and is manufactured on or after June 5, 2007, but before September 1, 2009. (b) For purpose of complying with S8.2, a manufacturer may count a vehicle if it: (1)(i) Is certified as complying with this standard and is manufactured on or after June 5, 2007, but before September 1, 2010; and (ii) Is not counted toward compliance with S8.1; or (2) Is manufactured on or after September 1, 2009, but before September 1, 2010. (c) For purposes of complying with S8.3, a manufacturer may count a vehicle if it: (1)(i) Is certified as complying with this standard and is manufactured on or after June 5, 2007, but before September 1, 2011; [...]

S8.6 Vehicles produced by more than one manufacturer. S8.6.1 For the purpose of calculating average annual production of vehicles for each manufacturer and the number of vehicles manufactured by each manufacturer under S8.1 through S8.4, a vehicle produced by more than one manufacturer must be attributed to a single manufacturer as follows, subject to S8.6.2: (a) A vehicle that is imported must be attributed to the importer. (b) A vehicle manufactured in the United States by more than one manufacturer, one of which also markets the vehicle, must be attributed to the manufacturer that markets the vehicle. [...]

Defined terms

The standard defines 15 terms in its definitions section; the first 12 are quoted here from the eCFR.

• Ackerman Steer Angle means the angle whose tangent is the wheelbase divided by the radius of the turn at a very low speed.
• Drive configuration means the driver-selected, or default, condition for distributing power from the engine to the drive wheels (examples include, but are not limited to, 2-wheel drive, front-wheel drive, rear-wheel drive, all-wheel drive, 4-wheel drive high gear with locked differential, and 4-wheel drive low gear).
• Electronic stability control system or ESC system means a system that has all of the following attributes:
• (2) That is computer-controlled with the computer using a closed-loop algorithm to limit vehicle oversteer and to limit vehicle understeer;
• (3) That has a means to determine the vehicle's yaw rate and to estimate its side slip or side slip derivative with respect to time;
• (4) That has a means to monitor driver steering inputs;
• (5) That has an algorithm to determine the need, and a means to modify engine torque, as necessary, to assist the driver in maintaining control of the vehicle; and
• (6) That is operational over the full speed range of the vehicle (except at vehicle speeds less than 20 km/h (12.4 mph), when being driven in reverse, or during system initialization).
• Lateral acceleration means the component of the vector acceleration of a point in the vehicle perpendicular to the vehicle's x-axis (longitudinal) and parallel to the road plane.
• Low-range four-wheel drive configuration means a drive configuration that has the effect of locking the drive gears at the front and rear axles together and providing an additional gear reduction between the engine speed and vehicle speed of at least 2.0.
• Mode means an ESC performance algorithm, whether driver-selected or not (examples include, but are not limited to, standard (default) mode, performance mode, snow or slippery road mode, or Off mode).
• Oversteer means a condition in which the vehicle's yaw rate is greater than the yaw rate that would occur at the vehicle's speed as a result of the Ackerman Steer Angle.

Limits of this page

This page quotes the text of 49 CFR 571.126 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 571.126, Standard No. 126; Electronic stability control systems for light 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)