Mr. Ken Daining
Supervisor, Vehicle Test and Development
ITT Automotive
3000 University Drive
Auburn Hills, MI 48326

Dear Mr. Daining:

This responds to your letter about Federal requirements applicable to an "on/off switch" for antilock brake systems (ABS). I apologize for the delay in our response. You stated that Chrysler Jeep owners disengage their ABS in response to the "perceived degraded performance it offers on off-road situations." You mentioned the possibility of designing a vehicle's gear system so that the ABS function is automatically disengaged when the vehicle is shifted into the four wheel drive-LO configuration. As explained below, while both manual and automatic ABS on/off switches are permitted under the current requirements, neither is required.

By way of background information, the National Highway Traffic Safety Administration (NHTSA) is authorized under Title 49, Chapter 301 of the U.S. Code to issue FMVSSs that set performance requirements for new motor vehicles and new items of motor vehicle equipment. NHTSA does not approve or certify any vehicles or items of equipment, as is the practice in Europe. Instead, Chapter 301 establishes a "self-certification" process under which each manufacturer is responsible for certifying that its products meet all applicable safety standards.

The agency has used this authority to issue FMVSS No. 105, Hydraulic Brake Systems, which specifies requirements for hydraulic service brake and associated parking brake systems. This Standard does not contain any provision requiring or prohibiting ABS. Likewise, it does not contain any provision requiring or prohibiting either a manual or automatic ABS on/off switch. Accordingly, either type of switch is permitted under the standard, provided the vehicle complies with the standard both when the device is "on" and when the device is "off."

FMVSS No. 105 will continue to apply to multipurpose passenger vehicles (MPVs), notwithstanding the agency's recent adoption of FMVSS No. 135 Hydraulic Brake Systems; Passenger Car Brake Systems, which applies only to passenger car brake systems (60 FR 6411, February 2, 1995). Even though FMVSS No. 135 does not apply to MPVs, you should be aware that FMVSS No. 135 prohibits passenger cars from being equipped with ABS disabling switches. The agency stated in a July 1991 notice that "such a switch could be left off when the ABS is needed, and that therefore, it would be more likely to be harmful than beneficial." Please note that this prohibition does not become immediately effective, even for passenger cars, since manufacturers can continue to certify compliance to FMVSS No. 105 for five years after FMVSS No. 135 takes effect.

If an automatic or manual ABS on/off switch were installed in a used vehicle, such a device must not "make inoperative" the vehicle's compliance with FMVSS No. 105. Specifically, 49 U.S.C. 30122 prohibits a motor vehicle manufacturer, distributor, dealer or repair business from installing such a device if the installation "makes inoperative" compliance with any safety standard. For instance, if a vehicle could only comply with the stopping distance or other service brake requirements in Standard No. 105 when the ABS is activated, then installation of the switch would serve to make inoperative compliance with the safety standard.

I hope you find this information helpful. If you have any other questions, please contact Marvin Shaw of my staff at this address or by phone at (202) 366-2992.


Philip R. Recht Chief Counsel

ref:105 d:3/8/95