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UN R131 Supplement 4 (01 series) · UNECE Regulation No. 131 (ECE R131) — Uniform provisions concerning the approval of motor vehicles with regard to the Advanced Emergency Braking System (AEBS) for M2, M3, N2 and N3 vehicles.

UN R131 — Supplement 4 to the 01 series of amendments

Supplement 3 → 4

Adopted at the WP.29 196th sessionEntry into force 2026-01-11
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What changed
  • Paragraph 5.4.1. now requires the AEBS function to be automatically reinstated “at each initiation of the powertrain”, instead of “at the initiation of each new engine start (or run cycle, as relevant)”.
  • A new engine start (or run cycle) performed automatically is not considered an “initiation of the powertrain” wherever that term is used in this Regulation.
Why
  • The United Kingdom proposal says that ‘engine’ or ‘run cycle’ implies a technology type and may retain a level of ambiguity.
  • The proposal aligns this Regulation with the ‘powertrain’ wording agreed at the twentieth session of GRVA for UN Regulations Nos. 79, 157 and 171.

Q1What changed3 changes

Reinstatement of the AEBS function at each initiation of the powertrain (para. 5.4.1.)

Paragraph 5.4.1. now requires the AEBS function to be automatically reinstated “at each initiation of the powertrain”. Before, it said “at the initiation of each new engine start (or run cycle, as relevant)”. A new engine start (or run cycle) performed automatically is not considered an “initiation of the powertrain” wherever that term is used in this Regulation. The paragraph gives the operation of a stop/start system as an example. The earlier sentence, “This requirement does not apply when a new engine start (or run cycle, as relevant) is performed automatically”, is deleted. A new footnote on “powertrain” refers to Mutual Resolution No. 2 (M.R.2) of the 1958 and the 1998 Agreements, document ECE/TRANS/WP.29/1121, for the definition.

The AEBS function shall be automatically reinstated at the each initiation of each the powertrain. A new engine start (or run cycle, as relevant).) which is performed automatically, e.g. the operation of a stop/start system, shall not be considered an “initiation of the powertrain” wherever that term is used in this Regulation.
This requirement does not apply when a new engine start (or run cycle, as relevant) is performed automatically, e.g. the operation of a stop/start system.
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Q2Why it changed

Proposed by
Expert from the United Kingdom of Great Britain and Northern Ireland
Working party
GRVA, 21st session (January 2025)

Reasons

  • At the twentieth session of GRVA, a new wording was agreed for UN Regulations Nos. 79, 157 and 171. It deals with the status of a system when the vehicle is switched off and then restarted. The agreement was to refer to the status of the ‘powertrain’ rather than the ‘engine’ or a ‘run cycle’. GRVA also agreed that this Regulation should be brought into alignment.

    Sources (3)
    “In the twentieth session of GRVA a new formulation of wording to deal with the status of a system when the vehicle is switched off and then restarted was agreed for UN Regulations Nos. 79, 157, and 171.”
    “The agreement was to refer to the status of the ‘powertrain’ rather than the ‘engine’ or a ‘run cycle’”
    “As a result, GRVA also agreed that this Regulation should be brought into alignment, hence the reason for bringing forward this proposal.”

  • Continuing to refer to ‘engine’ or ‘run cycle’ implies a technology type and may retain a level of ambiguity. M.R.2 created generic terms for components and aspects of propulsion systems that are independent of fuel type or technology used. Using the definition of ‘powertrain’ from M.R.2 gives a generic term and simplifies the respective provisions.

    Sources (4)
    “Continuing to refer to ‘engine’ or ‘run cycle’ is still implying a technology type and therefore may retain a level of ambiguity.”
    “created generic terms for components and aspects of propulsion systems that are independent of fuel type or technology used”
    “Using the definition of ‘powertrain’ from M.R.2 provides a generic term”
    “Also using the term ‘powertrain’ simplifies the respective provisions.”

  • This terminology further clarifies the agreed interpretation resulting from the consideration of GRVA-13-33. It is considered an improvement to the proposal that originally addressed it (GRVA-14-57).

    Source
    “Utilising this terminology further clarifies the agreed interpretation resulting from the consideration of GRVA-13-33 and is therefore considered an improvement to the proposal that originally addressed it (GRVA-14-57).”

Document trail

  1. 2024-11ProposalECE/TRANS/WP.29/GRVA/2025/8Proposal from the United Kingdom on the “engine start / run cycle” terminology
  2. —Working party adoptsECE/TRANS/WP.29/GRVA/21Session report, para. 105
  3. 2025-04Sent to WP.29ECE/TRANS/WP.29/2025/87Text that GRVA sent to WP.29 and AC.1
  4. 2025-06WP.29 adoptsECE/TRANS/WP.29/1186Adopted at the 196th session (session report, para. 111)
  5. 2026-01-11In forceC.N.38.2026.TREATIES-XI.B.16.131UN depositary notification

Q3Who is affected

Vehicle manufacturer

  • No direct action for this role.

Component supplier

  • No direct action for this role.

Technical service / Approval authority

  • No direct action for this role.

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ⓘ This report gives advice only. It is not legal or type-approval advice.

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