Mr. David Spurgess
Director Systems Engineering
12000 Tech Center Drive
Livonia, MI 48150
Dear Mr. Spurgess:
This responds to your letter requesting an interpretation of S7.8 of Federal Motor Vehicle Safety Standard (FMVSS) No. 135.You requested the Agencys concurrence with, or guidance regarding a suggested interpretation.You suggest that S7.8 is intended to require the testing of only a single antilock brake system (ABS) inoperative condition and that it is up to the discretion of the representative conducting the test to ensure that this has been accomplished appropriately.The issues raised by your letter are discussed below.
FMVSS No. 135 specifies requirements for service brake and associated parking brake systems for vehicles with a gross vehicle weight rating of 7716 pounds or less.The purpose of the standard is to ensure safe braking performance under normal and emergency driving conditions.Included in FMVSS No. 135 is S7.8, Antilock functional failure, which is part of a series of individual system functional failure tests.The series also includes: S7.7, Stops with engine off; S7.9 Variable brake proportioning system functional failure; S7.10, hydraulic circuit failure; and S7.11, Brake power unit or brake power assist unit inoperative.
S7.8 is a performance test conducted with an ABS functional failure simulation.In order to simulate a functional failure S7.8.2(g)(1) includes the following test specification: "Disconnect the functional power source, or any other electrical connector that creates a functional failure."
In your letter you state:
If a complex electrical control system is the basis for the ABS, it is feasible . . . that there are more then [sic] one electrical inputs into the module that may or may not directly apply to the performance of the ABS.
You state further:
[T]he purpose of S7.8 is to provide a performance requirement for a single condition of ABS inoperative. . . . [I]t is up to the discretion of the representative conducting the test to ensure that the selection [of which electric connector to disconnect] has been accomplished appropriately to ensure that only the ABS has been disabled and tested.
You are correct that S7.8 of FMVSS No. 135 is intended to be performed with a single function failure in the ABS only.In fact, each individual system functional failure test referenced above is intended to verify only the performance of the single failure type to which it directly applies.In the final rule establishing FMVSS No. 135 (60 FR 6411) the Agency clarified that in the antilock functional failure performance test only a single ABS failure is covered.Under S7.8, if the Agency were to test a complex system, such as your letter describes, the Agency would simulate ABS functional failure by disconnecting any electrical connector that creates only an ABS functional failure.The Agency may contact the manufacturer for assistance in determining how to perform this failure and for a procedure that does not impact or has limited impact on other systems.
However, when FMVSS No. 135 was established, the Agency recognized the increasing integration of ABS into the service brake system.The Agency noted "if a functional failure of the ABS also affects or degrades the service brake system, no artificial means are [employed] to keep the service brake system intact when that failure is introduced." Therefore, if the electric control system for the ABS is designed such that an ABS failure cannot be isolated and simulated under S7.8 without also affecting some other braking function, then the antilock functional failure requirements must be met with both the ABS failure and the additional braking function failure.
I hope you find this information helpful.If you have any further questions please contact Chris Calamita of my office at this address or by phone at (202) 366-2992.