Interpretation ID: nht95-6.37

TYPE: INTERPRETATION-NHTSA

DATE: September 6, 1995

FROM: Earl Eisnhart -- Vice President, National Private Truck Council; Larry W. Strawhorn -- Vice President - Engineering, American Trucking Associations

TO: John G. Womack -- Acting Chief Counsel, NHTSA

TITLE: NONE

ATTACHMT: ATTACHED TO 10/30/95 LETTER FROM JOHN WOMACK TO LARRY W. STRAWHORN (A43; STD. 121)

TEXT: Dear Mr. Womack:

This letter is a request for an interpretation of Section 5.2.3.3, Antilock Malfunction Indicator, of Federal Motor Vehicle Safety Standard (FMVSS) 121, Air Brake Systems, which requires an antilock malfunction indicator lamp to be mounted on trailers during an eight year transition period. This section reads (second sentence emphasized):

"S5.2.3.3 Antilock Malfunction Indicator. Each trailer (including trailer converter dolly) manufactured on or after March 1, 1998 and before March 1, 2006 shall be equipped with a lamp indicating a malfunction of a trailer's antilock brake system. Such a lamp shall remain activated as long as the malfunction exists whenever power is supplied to the antilock brake system. The display shall be visible within the driver's forward field of view through the rearview mirror(s), and shall be visible once the malfunction is present and power is provided to the system."

Since this requirement does not specify a specific "activation pattern", we interpret that the agency expects the industry itself to standardize on an activation pattern. This is consistent with the agency's position in Section 5.1.6.3, Antilock Power Circuit for Towed Vehicles, where NHTSA is relying on the industry to determine the most effective way to provide separate power to trailer antilock systems.

Section 5.1.6.2, Antilock Malfunction Circuit and Signal, which requires in-cab mounted malfunction lamps for towing and towed vehicle(s) antilock systems does not specify an actuation pattern for malfunction lamps on powered vehicles either. However, the section in the rule preamble which discusses the in-cab malfunction lamp on powered vehicles, Activation Protocol for Malfunction Indicators (page 13246 Federal Register/Vol. 60, No. 47), makes it clear that NHTSA wants the activation pattern for truck/tractor in-cab lamps to be such that "upon a failure, the lamp would activate and provide a continuous yellow signal" and would "have a continuously burning lamp in response to a malfunction." This preamble section does not discuss trailer mounted malfunction lamps.

The special SAE ABS task force, which was established last April to develop, or modify, standards and recommended practices in areas of vehicle design and performance affected by the new antilock requirements of FMVSS 121, has developed a recommendation for trailer mounted malfunction lamps which most effectively meets the needs for the lamp.

Among the task force's recommendations is one that the lamp activation pattern should be such that the lamp bulb be ON when the antilock system is working properly and OFF when a malfunction exists, the antilock system is not getting electrical power, or the lamp bulb is burnt out.

Adoption of this trailer malfunction lamp activation pattern for trailers during the eight year transition period provides significant safety advantages including:

(1) The lamp activation pattern becomes a fail safe pattern, i.e., it will signal an inoperative antilock system even when the system is not receiving electrical power or the lamp bulb is burnt out. A lamp system which activates by turning the lamp ON when there is a malfunction will not warn of antilock failures under these conditions.

(2) The recommended activation pattern fits in with pre-trip walk-around and other trailer inspections. In walk-around inspections, where drivers turn ON all the lamps including the stop lamps (brakes applied through use of the trailer hand valve, trailer air supply valve, stick prop, etc.) and then walk around the vehicle to detect if any lamps (this would include the antilock lamp) are not burning. This inspection is simpler and more reliable if the driver doesn't have to go through a lamp check procedure first. The same is also true when mechanics and officials inspect the trailer.

We respectively request that you advise us as soon as possible Whether our interpretation of Section 5.2.3.3, i.e., does not require a specific lamp activation pattern, is correct. New tractors must start complying with the new antilock system requirements in 18 months. In order for tractor manufacturers to efficiently design their vehicles to accommodate trailer antilock system malfunction signals, they need to know the standard protocol for these signals soon. In order for antilock manufacturers to standardize the protocol, they need to know if our interpretation is correct.

Please contact us if there is a need for further information.