Interpretation ID: 23394.jeg
- James Chen, Esq.
Hogan & Hartson L.L.P.
555 13th Street, NW
Washington, DC 20004-1109
Fax: 202-637-5910
William Kurtz, Manager
Environmental & Safety Engineering Department
Mercedes-Benz USA, LLC
One Mercedes Drive
P.O. Box 350
Montvale, NJ 07645-0350
Dear Mr. Kurtz:
This responds to your request for an interpretation of Federal Motor Vehicle Safety Standard No. 135. You asked for our concurrence that "S5.3.2 Controls, which prohibits 'a control to manually disable the ABS, either fully or partially' does not prohibit the transmission's electronic control unit from automatically disengaging the ABS when the central differential is locked in an off-road driving mode." You asked your question in connection with the G-class multipurpose passenger vehicle (MPV).
By way of background information information, the National Highway Traffic Safety Administration does not provide approvals of motor vehicles or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, it is the responsibility of the manufacturer to ensure that its vehicles and equipment comply with all applicable standards. The following opinion is based on the facts provided in your letter and in telephone conversations with your attorney, James Chen, Esq., and stated in this letter.
As discussed below, it is our opinion that S5.3.2's prohibition of a control that manually disables ABS does not apply to a vehicle setting where the vehicle can, as a practical matter, only be driven for off-road operations. Since, based on the information provided in your letter and by Mr. Chen, the G-class MPV cannot, as a practical matter, be driven on paved roadways when the central differential is locked, the S5.3.2 prohibition does not apply in this situation.
I will now explain our position.
S5.3.2 reads as follows:
For vehicles equipped with ABS, a control to manually disable the ABS, either fully or partially, is prohibited.
In proposing this provision in July 1991, we included the following discussion:
Some manufacturers have argued that [an antilock disabling switch], which would enable a driver to turn off the ABS, would be useful in conditions such as mud or deep snow, where a locked wheel could produce shorter stops than a rolling wheel. However, NHTSA agrees with the position taken by the GRRF that such a switch could be left off when the ABS is needed, and that therefore, it would be more likely to be harmful than beneficial. 56 FR 30538, July 3, 1991.
Thus, the purpose of the provision is to prevent situations where a vehicle's ABS is needed but is not available because the driver has turned it off.
According to your letter, when a driver of the G-class MPV locks the central differential for off-road operation, the ABS system is disengaged. You suggest that this type of system should not be considered to be prohibited by S5.3.2, because the ABS system is disengaged "automatically," as a result of the vehicle having its central differential locked, rather than manually.
We disagree with the view that the ABS system is not being disengaged manually in this situation. The word "manually," as used in S5.3.2, has reference to action by the driver. If activation of a particular control by the driver results in the ABS being disengaged, we would consider the control to manually disable the ABS, regardless of whether the control also does something else, such as locking the central differential.
In light of other information provided by you and by Mr. Chen, however, we nonetheless believe that the S5.3.2 does not apply in the situation you describe. As noted above, the purpose of the S5.3.2 prohibition is to prevent situations where a vehicle's ABS is needed but is not available because the driver has turned it off. In light of this purpose, we believe it is appropriate to interpret the provision as not applying to a vehicle setting where the vehicle can, as a practical matter, only be driven for off-road operations.
According to your letter, the ABS system of the G-class MPV is disengaged only when the central differential is locked. We also understand from Mr. Chen that if the central differential is unlocked, the ABS system is always engaged again.
You stated that with the central differential locked, a vehicle setting intended only for off-road use, all four wheels rotate at the same speed. Operation of the vehicle in this manner on hard road surfaces would result in serious wheel chatter, hard steering and risk of serious damage to the transmission. There is also a yellow warning label adjacent to the differential lock switches which states: "Warning! Never use differential locks on paved roads! Engaged differential locks limit the ability to move around curves."
Given the above facts, we conclude that, for the G-class MPV, locking of the central differential is a vehicle setting where the vehicle can, as a practical matter, only be driven for off-road operations. Accordingly, the S5.3.2 prohibition does not apply in this situation.
I hope this information is helpful. If you have any further questions, please feel free to call Edward Glancy of my staff at 202-366-2992.
Sincerely,
John Womack
Acting Chief Counsel
cc:
NCC-20 :EGlancy :mar :10/16/01 :62992 :OCC 23394
cc: NCC-01 Subj/Chron
interps/135/23394.jeg
concurrence: NPS, NSA, Redbook (2), interp. Std. 135