Interpretation ID: aiam1720
Corporate Attorney
Eaton Corporation
100 Erieview Plaza
Cleveland
OH 44114;
Dear Mr. Horst: This responds to your November 22, 1974, request for an interpretatio of language in Standard No. 121, *Air brake systems, that regulates electrical failure of the antilock systems which may be installed by vehicle manufacturers to meet the standard's performance requirements. You ask whether the S5.1.6 requirement for a continuous warning light 'in the event of total electrical failure' includes (1) any failure within the antilock system other than complete loss of all electrical power, or (2) any failure in the vehicle power source to the antilock components or from the antilock components to the signal lamp in the driver's compartment. You also ask whether the S5.5.1 requirement that 'electrical failure of any part of the antilock system shall not increase the actuation and release times of the service brakes' permits an increase in actuation time while the antilock logic circuity (sic) first recognizes a failure that occurs during brake actuation and then deactivates the antilock system.; In responding to a similar request for interpretation on the meaning o 'total electrical failure' we interpreted this phrase in a May 26, 1972, letter to Wagner Electric to mean any electrical failure within the antilock electrical system circuitry which would cause loss of antilock control of every wheel on the vehicle. This requires that the signal activate when complete loss of electrical power is sensed within the antilock system. We understand that many available systems also signal partial loss of electrical integrity, and we may give future consideration to a requirement that the signal activate in response to specific 'partial failures.'; With regard to failures in the battery or in the wiring from th battery to the antilock or from the antilock to the signal in the driver's compartment, we cannot state that a failure in these systems would not be non-compliance with S5.1.6. Our other standards (e.g., *Lamps, reflective devices, and associated equipment) assume and require the integrity of the wiring systems necessary to meet the requirement. Of course an isolated case of battery failure or a broken wire to the signal lamp would not in itself be considered a non-compliance. It would appear that a manufacturer of antilock systems is not in a position to certify that the signal generated by his product will reach the dashboard.; You pointed out that, with regard to S5.5.1's requirement tha 'electrical failure of any part of the antilock system shall not increase the actuation and release times of the service brakes,' the possibility exists of an antilock electrical failure occurring during a brake application which would necessitate a period for recognition of the failure and deactivation of the system. This recognition period would increase the actuation time. The NHTSA believes that this period of initial recognition is desirable to detect and eliminate incorrect indications of malfunction without interfering with the antilock function. Until the wording of this section is modified to reflect this exception, the NHTSA interprets S5.5.1 to permit an increase in actuation time while antilock logic circuitry first recognizes a failure occuring (sic) during brake actuation, and deactivates the antilock system.; Yours truly, Richard B. Dyson, Acting Chief Counsel