Interpretation ID: nht75-6.21

DATE: 02/28/75

FROM: RICHARD B. DYSON -- NHTSA ASSISTANT CHIEF COUNSEL

TO: GERHARD P. RIECHEL -- ATTORNEY VOLKSWAGEN OF AMERICA, INC.

TITLE: N40-30

ATTACHMT: LETTER DATED 12/11/74 FROM GERHARD P. RIECHEL TO TAYLOR VINSON -- NHTSA, STANDARD 105-FAILURE INDICATOR LAMP

TEXT: Dear Mr. Riechel:

This responds to Volkswagen's December 11, 1974, request for a determination that a brake system indicator lamp which activates only upon application of the brake pedal with a control force of 50 pounds or more to signal a "gross loss of pressure" would meet the requirement of S5.3.3 of Standard No. 105-75, Hydraulic brake systems:

S5.3.3 Each indicator lamp activated due to a condition specified in S5.3.1 shall remain activated as long as the condition exists, whenever the ignition (start) switch is in the "on" ("run") position, whether or not the engine is running.

Your question arises as to the meaning of the phrase in S5.3.3 which requires that the lamp "remain activated as long as the condition exists", with reference to the condition described in S5.3.1(a) as "gross loss of pressure (such as caused by rupture of a brake line but not by a structural failure of a housing that is common to two or more subsystems)". You point out that a condition involving loss of pressure cannot exist in the absence of pressure, that is, after control force is removed from the brake pedal.

While the NHTSA has always believed that the requirement in question can best be satisfied by an indicator lamp which remains activated after the loss of pressure has occurred, we agree that the language in question could be more clearly drafted to express this intent. Accordingly, we plan to propose an amendment to the standard to eliminate this ambiguity. The proposed effective date of the amendment

will be far enough in the future so that any new design changes required to comply may be effected without undue burden on affected manufacturers.

Because we conclude that the reliance Volkswagen has placed on its alternative reading of S5.3.3 can be justified in this case, we would accept the limited warning offered by the system you describe as satisfying the current requirement in S5.3.3 with regard to S.5.3.1(a).

Yours truly,