Mr. Robert M. Clarke

President

Truck Manufacturers Association

225 New York Ave. NW

Suite 300

Washington, DC 20005

Dear Mr. Clarke:

This responds to your letter, co-signed by Mr. Timothy Kraus of the Heavy Duty Brake Manufacturers Council, requesting an interpretation of Federal Motor Vehicle Safety Standard (FMVSS) No. 121, Air Brake Systems. We are sending an identical letter to Mr. Kraus.

You asked that we confirm your interpretation of the requirements of FMVSS No. 121 as they relate to the check of lamp function for the in-cab indicator lamp used to signal an antilock brake system malfunction in a towed unit. For reasons discussed below, we agree that S5.1.6.2(b) of the standard does not require a check of lamp function for the in-cab trailer ABS malfunction lamp when there is no post-2001 trailer or towed unit attached to the tractor. (As with your letter, we refer for purposes of convenience to trailers subject to the relevant ABS requirements as post-2001 trailers and ones built before those requirements applied as pre-2001 trailers.)

By way of background, the National Highway Traffic Safety Administration (NHTSA) is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment (see 49 U.S.C. Chapter 301). NHTSA does not approve motor vehicles or motor vehicle equipment; nor do we endorse any commercial products. Instead, each manufacturer must self-certify that its products meet all applicable safety standards prior to sale.

Paragraph S5.1.6.2(b) of FMVSS No. 121 requires truck tractors and single unit trucks that are equipped to tow another air braked vehicle to be equipped with an in-cab indicator lamp (separate from the lamp for the tractor or truck required by S5.1.6.2(a)) which is to be activated whenever the malfunction signal circuit detects an ABS malfunction on a towed vehicle. The indicator lamp must also be activated as a check of lamp function whenever the ignition is turned to the on (run) position, and deactivated at the end of the function unless a trailer ABS malfunction signal is present.

In your letter, you stated that the members of HDBMC and TMA generally agree that the best interpretation of S5.1.6.2(b) is that there is no requirement to perform a check of lamp function for the in-cab trailer ABS malfunction indicator lamp when there is no post-2001 trailer or towed unit attached to the tractor. In support of this view, you made several arguments, including the following:

. . . the requirements of S5.1.6.2(b) as a whole make sense only in the context of the presence of a post-2001 trailer that is connected to the tractor. . . . the first sentence of the section clearly states that the tractor electrical circuit must be capable of transmitting an ABS malfunction signal from the antilock brake system(s) on one or more towed vehicle(s). The second sentence of the section clearly states that the in-cab lamp shall be activated whenever the malfunction signal circuit described above receives a signal indicating ABS malfunction. The last sentence of the section requires deactivation of the indicator lamp after the check of lamp function unless a trailer ABS malfunction signal is present. These requirements clearly envision a tractor that is connected to a post-2001 trailer. (All emphasis added by HDBMC/TMA)

You stated that consistent with this understanding, SAE Recommended Practice J2497 (October 2002) states that the logical control of the in-cab trailer ABS indicator lamp shall be made by a device on the trailer. You stated further that according to SAE J2497, the trailer ABS device initiates the power up (bulb check) logic sequence when power is applied and the trailer ABS device becomes active, and [i]f no lamp control messages are received [from the ABS device on the trailer], then the tractor device will not perform a bulb check [on the in-cab trailer ABS indicator lamp].

You indicated that SAE J2497 was issued upon the recommendation of the SAE Truck and Bus Power Line Carrier Task Force. According to your letter, records from those deliberations indicate that there was concern among human factors experts working on the proposal that having the in-cab trailer ABS malfunction indicator activate as a check of lamp function when either a pre-2001 trailer was present or when no trailer was present at all would, at a minimum, confuse drivers or, worse, incorrectly lead them to believe the trailer they were towing was equipped with functioning ABS. In this regard, you noted that, as explained by NHTSA in the preamble to the final rule establishing these requirements, NHTSA has decided to require the malfunction indicator lamp to activate when a problem exists and not activate when the system is functioning properly. Thus, extinguishing the malfunction lamp at the end of the check of lamp function signals proper functioning of the trailer ABS system, which would not be the case if there was no post-2001 trailer connected to the tractor (or single unit truck that is equipped to tow another air-braked vehicle).

After considering the overall language of S5.1.6.2(b) and its purposes, and the arguments presented in your letter, we confirm that this paragraph does not require a check of lamp function for the in-cab trailer ABS malfunction lamp when there is no post-2001 trailer or towed unit attached to the tractor. S5.1.6.2(b) states, in relevant part:

Each . . . truck tractor and single unit vehicle shall also be equipped with an indicator lamp, separate from the lamp required in S5.1.6.2(a), mounted in front of and in clear view of the driver, which is activated whenever the malfunction signal circuit described above receives a signal indicating an ABS malfunction on one or more towed vehicle(s). The indicator lamp shall remain activated as long as an ABS malfunction signal from one or more towed vehicle(s) is present, whenever the ignition (start) switch is in the on (run) position, whether or not the engine is running. The indicator lamp shall also be activated as a check of lamp function whenever the ignition is turned to the on (run) position. The indicator lamp shall be deactivated at the end of the check of lamp function unless a trailer ABS malfunction signal is present.

49 CFR 571.121, S5.1.6.2(b) (2006).

In interpreting the relevant language, we note that the requirement specifying that the indicator lamp must be activated as a check of lamp function whenever the ignition is turned to the on (run) position does not expressly state whether it applies in situations where there is no post-2001 trailer attached. This is relevant in the context of S5.1.6.2(b) because the in-cab trailer ABS malfunction lamp itself only indicates malfunctions when a post-2001 trailer is attached. Moreover, the sentences immediately preceding the specific one at issue contemplate a post-2001 trailer being attached to the tractor. Given this, we believe that it is reasonable to read the requirement for check of the in-cab trailer ABS lamp function as applying only when a post-2001 trailer is attached.

In providing this interpretation, we have considered the issues you raise concerning avoiding potential confusion. Of particular concern is the possibility of drivers mistakenly believing they are towing a functioning ABS-equipped trailer when they are not as a result of observing an in-cab trailer ABS malfunction lamp activating and then extinguishing when no ABS-equipped trailer is connected to the tractor.

Please bear in mind, however, that the purpose of the check of lamp function is to alert drivers to problems with the bulb or the electrical system. We note that under this interpretation, the requirement that the in-cab trailer ABS indicator lamp must be activated as a check of lamp function whenever the ignition is turned to the on (run) position applies whenever the vehicle is towing a post-2001 trailer, i.e., the situations where the in-cab trailer ABS malfunction lamp will operate.

We note that this interpretation reflects the very specific language and policy concerns discussed in this letter. This interpretation applies only to this particular situation, and should not be read as an interpretation of how we would interpret requirements for check of lamp function in any other situation.

 

If you have any further questions, please contact Rebecca Schade of my staff at (202) 366-2992.

Sincerely,

Anthony M. Cooke

Chief Counsel

d.3/5/07

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