Brake-by-Wire in Chinese EVs: One-Box EHB, Dry EMB, GB 21670-2025, and UN R13-H Homologation Procurement Guide

Brake-by-wire in Chinese EVs uses electronic sensing and control to coordinate the driver's braking request with friction braking and regenerative braking. One-Box electro-hydraulic braking (EHB) retains hydraulic wheel brakes; fully dry electro-mechanical braking (EMB) applies the friction brakes using electrical wheel-end actuators. These labels describe architectures, not a vehicle's approval status or its behavior after a failure.

For commercial vehicle importers, automotive distributors, and fleet procurement directors, a manufacturer's claim of "intelligent by-wire braking" or "ASIL-D chassis safety" does not establish whether the offered vehicle can be registered, maintained, or insured in the destination market. Buyers need three connected records: the exact vehicle configuration, its applicable approval evidence, and a workable local service plan.

Quick procurement answer: Before placing a batch order, obtain the destination approval route for the exact variant, the documented degraded-braking concept, and a demonstration that your destination workshop can access the OEM's required diagnostic functions. Do not treat a Chinese GB filing, an ASIL claim, or a supplier brochure as a substitute for vehicle-level approval. Budget replacement parts and diagnostic access alongside any expected regenerative-braking savings.

Already evaluating a vehicle shortlist? Send your target models, destination country, and fleet duty cycle with a sourcing inquiry, or explore our electric vehicle export catalog before requesting variant-specific evidence.

Published and reviewed: November 7, 2026. Scope: English-language procurement guidance for global buyers of China-built passenger EVs; vehicle category and destination rules must be checked separately. Method: a desk review of the public documents linked below, combined with an original document-request checklist and an illustrative fleet-cost calculation. We have not performed vehicle, dynamometer, failure-injection, or workshop tests. Public sources do not establish any offered VIN's brake hardware, diagnostic compatibility, or approval. The latest consolidated UN R13-H text and destination-specific amendments were not independently reviewed; the regulatory matrix is an evidence-request framework, not a clause-by-clause equivalence opinion.

Cover image: a vehicle catalog illustration, not evidence of the pictured vehicle's brake supplier or hydraulic layout.

1. Executive Summary & Key Procurement Conclusions

Before signing distribution agreements, use five verification gates:

1. Separate domestic compliance from destination approval. Establish the vehicle category, approval authority, accepted regulation series, and approval route. A domestic-market vehicle and an export variant with the same retail name may have different documentation and software.
2. Identify the actual architecture. Request the brake assembly part number, software identifier, and circuit drawing. One-Box integration can reduce packaging complexity, but it does not establish a universal response time, replacement price, or mechanical backup layout.
3. Prove service access. A scanner that reads fault codes may not support the OEM's bleeding, replacement coding, calibration, or security authorization functions. Obtain a demonstration on the offered configuration.
4. Request fault-specific braking evidence. Distinguish loss of assist, failure of one circuit, loss of an electrical feed, and controller faults. Do not replace those separate test cases with one advertised residual-deceleration number.
5. Check delivered software behavior. Record accelerator-release behavior, stop-lamp operation, and brake-pedal response with the destination software build. Treat energy savings as something to measure during fleet acceptance, not a guaranteed consequence of the One-Box label.

2. Architectural Evolution: Vacuum Booster to One-Box and Dry EMB

EVs need a source of brake assistance independent of engine intake vacuum. An electric vacuum pump is one option; electromechanical boosting and integrated electro-hydraulic systems are others. The following diagram is a classification aid rather than a claim that every Chinese OEM follows one production timeline.

Vacuum-assisted hydraulic brakes
    -> electric booster + separate ESC hydraulic unit (Two-Box)
    -> integrated assistance + stability-control unit (One-Box EHB)

Separate design option: electrical wheel-end friction actuation (dry EMB)

Two-Box EHB

A Two-Box arrangement separates the booster from the electronic stability control hydraulic unit. It can support regenerative coordination and driver assistance; the label alone does not tell you whether the pedal is fully decoupled. Evaluate the particular booster, ESC, fallback path, and software integration together. Do not assume a Two-Box vehicle has inferior stopping performance solely because it contains two assemblies.

One-Box EHB

One-Box systems integrate functions that otherwise require separate assemblies. As a documented example, Bosch's integrated power brake combines brake boosting and stability control. Its product page describes sensed pedal demand, pedal decoupling, a feel simulator, and motor-driven hydraulic pressure generation.

That page lists up to 150 ms time-to-lock and up to 0.3 g recuperation. These are supplier product descriptors, not a universal 0-to-100-bar test result or proof of a particular Chinese EV's performance. Ask for test definitions, system generation, and vehicle-specific results before comparing offers. Do not convert the time figure directly into meters of stopping-distance improvement.

Dry EMB

Fully dry EMB removes the hydraulic service-brake transmission at the relevant wheels and uses electrical actuation to clamp friction pads against discs. Friction brakes, pad inspection, wear management, and actuator servicing remain necessary. Mixed hydraulic/electromechanical layouts must be identified separately.

An offered EMB vehicle needs documented power availability, fault containment, thermal limits, and approved degraded operation. Neither a demonstration vehicle nor a supplier announcement proves that the export variant has production approval and service support. This guide does not assign a commercial rollout date or prescribe a universal supply voltage.

3. Decoupled Electro-Hydraulic Circuit & Fail-Safe Bypass Architecture

The useful engineering question is: Which braking functions remain after each specified failure, and what evidence supports that answer?

One-Box Hydraulic Circuit Schematic

This conceptual flow diagram shows control and energy paths. It is not a plumbing diagram, valve-state map, or repair instruction for any model.

NORMAL OPERATION — conceptual decoupled EHB

Driver pedal -> demand sensors -> brake controller
     |                              |
     v                              +-> traction system -> regeneration
Pedal feel simulator                |
                                    +-> hydraulic actuator -> wheel brakes

FAILURE RESPONSE — configuration-specific

Detected fault -> warning + documented degraded operating mode
                         |
                         +-> hydraulic pedal fallback, if provided
                         +-> redundant electrical actuation, if provided

Acceptance evidence: fault case + remaining functions + measured performance

Some EHB designs provide a hydraulic pedal fallback when assistance is unavailable. Others rely on additional electrical redundancy for specified functions. A physical fallback path does not mean the vehicle retains normal pedal effort, ABS, stability control, or automatic emergency braking. An automatic stop without driver intervention is also a different requirement from driver-operated secondary braking.

Request a fault matrix identifying the failed component or supply, remaining energy source, available wheel circuits, warning behavior, pedal effort, and applicable test result. Match the report to the offered hardware and software versions. A common marketing term does not establish that every Chinese EV uses normally-open valves feeding the front axle.

Use the manufacturer's safety documentation and the appointed technical service to define any failure testing. Disconnecting a battery or disabling a controller on an ordinary road is not an acceptance method supplied by this guide.

4. Deceleration Blending: Cooperative Regenerative Braking System (CRBS)

Regenerative blending coordinates traction-motor braking with friction braking to meet the requested deceleration. Available regenerative torque depends on speed, battery state of charge, temperature, traction conditions, and powertrain limits. It may be unavailable even during light braking.

Requested deceleration
        |
        +-> regeneration available? -> use within current limits
        |
        +-> remaining demand -> friction braking

Near standstill / full or cold battery / limited traction:
friction contribution and control transitions depend on vehicle calibration.

There is no universal 0.3 g threshold below which every One-Box EV uses zero hydraulic pressure, nor a universal speed at which regeneration switches off. The buyer's acceptance question is whether the car maintains predictable deceleration and pedal response as available regeneration changes.

Commercial Fleet Economic Value

Regeneration can reduce traction-energy demand and friction-brake use, but architecture alone cannot predict a percentage saving or pad life. Frequent short trips, terrain, payload, charging practice, driver behavior, and brake corrosion can change the economics. Low friction-brake use does not remove inspection or fluid-maintenance obligations.

For a pilot fleet, record electricity consumption using the same measurement boundary, preferably charging-meter energy per kilometer, and log mileage, route, payload, ambient conditions, battery temperature, and state of charge. Track pads, discs, brake-fluid service, downtime, and fault history separately. A comparison between different vehicle models must disclose other differences; it cannot isolate the causal benefit of One-Box EHB by itself.

5. Regulatory Matrix: China GB 21670-2025 vs. UNECE UN R13-H

A Chinese compliance record and a destination approval dossier answer different questions. Start with the destination authority's accepted route, not an assumption that one document applies globally.

Standard Identification & Effective Dates

The official SAMR/SAC record for GB 21670-2025 identifies the passenger-car braking standard, published May 30, 2025, with an implementation date of January 1, 2026. Clause transitions require separate attention; see Section 6.

UN Regulation No. 13-H concerns passenger-car braking approval. Confirm the applicable category, amendment series, supplements, and destination recognition with the approval authority or technical service. The UNECE vehicle-regulation directory is an official starting point for locating texts; it is not itself a vehicle approval or a consolidated R13-H document. This guide does not establish an automatic EU, UK, GCC, Australian, or other global approval route.

An ASIL-D claim is not a universal statutory certificate requirement. ISO 26262 addresses functional safety; classification and safety goals arise from the development safety analysis. The linked ISO 26262-1:2018 record is specifically Part 1, Vocabulary, not a certificate for a brake product. Obtain the relevant safety evidence and its scope rather than treating a logo as homologation.

6. The Single-Pedal Driving Mandate: GB 21670-2025 Impact on Exports

Default behavior and transition dates

A notice published on the Chongqing municipal government website explains that accelerator-release braking in the default operating state should not bring the vehicle to a stop. It distinguishes the general January 1, 2026 implementation for newly submitted types from January 1, 2027 for the one-pedal provision, and gives January 1, 2027 for types already approved. Confirm the controlling standard's transition provisions for the actual vehicle; the headline implementation date alone is insufficient.

The notice also discusses stop-lamp activation above 1.3 m/s² regenerative deceleration. That is not a complete global lighting rule: confirm the applicable text, operating mode, and destination requirements with the technical service.

Sourcing implications

Record the default mode after startup, available driver selections, software version, and owner-manual description. Do not infer that every car built in 2026 already has the same default setting, that an existing car must receive a particular OTA change, or that every manufacturer must implement an identical creep function.

For exports, request the approved destination configuration and verify delivered behavior against it. Domestic inventory is not automatically eligible for conversion through a menu setting or unofficial firmware change. Driver training should explain regeneration limits and use of the brake pedal without claiming an accident-causation finding that this guide has not established.

7. Engineering Benchmark: Braking Architectural Paradigms

Compare the offered configuration using evidence under common test conditions. The following matrix intentionally avoids universal mass, pressure, recovery-efficiency, and stopping-distance rankings: public architecture labels do not supply those measurements.

8. Tier-1 Supplier Benchmark: Chinese EV Production Implementations

A supplier name is useful for traceability, but retail model names do not reliably establish supplier, part generation, destination calibration, or aftermarket tool access. This review does not verify Bosch, Bethel WCBS, Continental MK C2, FinDreams, Tongyu, or NASN fitment to specific vehicle models. Obtain a build-sheet entry or parts-catalog record for the offered VIN range instead of copying a supplier-to-model list into the purchase contract.

Use the same evidence matrix for each supplier offer:

Bosch's public IPB page supports an architecture example, not a list of confirmed fitments or universal scan-tool compatibility. UDS is a diagnostic service framework and DoIP a diagnostic transport; neither proves that a particular aftermarket scanner can perform a protected OEM routine. Demonstrate the required function on the intended configuration.

Include the offered brake part numbers and unresolved documentation in your sourcing inquiry so the supplier request can focus on evidence that is still missing.

9. Workshop Aftersales, Hydraulic Bleeding & Collision Repairability

Overseas service readiness is a procurement deliverable. Do not release a vehicle into service after hydraulic work merely because a warning light has cleared. The responsible workshop needs the correct procedure, authorized tooling, completion criteria, and documented release checks.

Six-point workshop readiness checklist

This is a documentation and capability checklist, not a universal bleeding procedure. Actual brake work belongs to qualified technicians using the exact OEM instructions.

1. Identify the system. Match the vehicle, assembly, software, and service document revision. Distinguish a routine fluid change from a dry system, opened hydraulic circuit, or assembly replacement.
2. Confirm energy and safety requirements. Obtain the OEM instructions for preventing unintended actuation, managing stored pressure, and providing the specified electrical support. Do not infer a safe depressurization state from a generic scanner reading.
3. Prove diagnostic capability. Confirm any required valve-cycling routines, security authorization, account region, and supported tool version. Manual or pressure bleeding may be permitted for some operations; the OEM procedure determines when a diagnostic routine is necessary.
4. Obtain exact consumable and tool specifications. Record approved fluid, pressure-equipment requirements, sequence, and torque data from the vehicle manual. DOT labels alone do not establish viscosity class or interchangeability; this guide does not prescribe DOT 5.1 as a substitute for a specified low-viscosity fluid.
5. Confirm replacement and calibration access. Document coding, adaptation, and calibration requirements, including account and connectivity dependencies. Ask who supports a failed routine and how an immobilized vehicle is handled.
6. Define release evidence. Require the OEM's completion checks, fault review, and controlled brake-performance verification by the qualified service provider. Keep the work order, software identifiers, and inspection results with the vehicle record.

Collision repair vulnerability and parts TCO

An integrated assembly can create a larger single replacement item, but mounting location, impact exposure, repairability, and price vary. Obtain a parts diagram and written quotation for the complete unit, any separately serviceable components, labor, coding, freight, taxes, and expected downtime. Do not treat an illustrative price as a current supplier quote.

Ask the insurer and repair network how they assess hydraulic block, mounting, harness, and connector damage. A repair policy must distinguish OEM-authorized repairs from component substitution. Include expected dispatch and delivery times separately; expedited dispatch does not guarantee customs clearance or a repaired vehicle.

Electronic parking brake and recovery

Electronic parking brake (EPB) layout and recovery procedures are vehicle-specific. Provide the recovery operator with the OEM recovery sheet, approved power-support points, and authorized transport method. There is no universal Torx size, hex-key size, winding direction, or rear-caliper release procedure. Do not dismantle an EPB actuator or force a piston based on this article; use the approved recovery arrangement when the vehicle cannot be released normally.

10. Importer Diligence: Five-Gate Procurement Checklist

Attach the checklist to the RFQ and assign an owner and due date to each unresolved item. A missing safety or approval record should remain an open condition rather than being silently converted into a supplier assurance.

Gate 1: Type approval and regulatory dossier

• Identify the destination authority, vehicle category, approval route, and accepted regulation version.
• Obtain variant-specific approval evidence and supporting electronic-control assessment where applicable.
• Match braking failure-test conditions and results to the offered vehicle configuration.
• Resolve applicable GB transitions and destination stop-lamp requirements with the homologation adviser.

Gate 2: Hardware architecture and sourcing clarity

• Record brake supplier, OEM part number, software version, and VIN applicability.
• Obtain the circuit or system description and documented degraded modes.
• Identify electrical dependencies, mounting exposure, and authorized replacement boundaries.

Gate 3: Workshop tooling and diagnostic access

• Demonstrate required service functions using the destination workshop's tool and account.
• Secure readable OEM documentation for fluid, bleeding, calibration, and recovery.
• Price licenses, subscriptions, equipment, training, and support escalation.

Gate 4: Regenerative calibration and driver acceptance

• Record startup defaults, selectable modes, and delivered destination software.
• Agree controlled acceptance checks for changing regenerative availability and pedal response.
• Provide driver and recovery instructions in the required language.

Gate 5: Spare parts and warranty commitments

• Obtain written parts prices, availability, coding requirements, and logistics estimates.
• Establish warranty exclusions, labor reimbursement, diagnostic evidence, and support ownership.
• Negotiate downtime and parts-support targets; do not assume a standard warranty or dispatch SLA.

11. Commercial Fleet TCO Sensitivity Analysis

The following hypothetical planning scenario is not observed fleet data, a supplier quotation, or a forecast of One-Box savings. It illustrates how to compare potential operating benefits with service and collision exposure. A competing modern EV may already offer effective regenerative blending, so its measured baseline could eliminate the assumed energy advantage entirely.

Assume 100 vehicles, 80,000 km per vehicle per year, and a three-year period: 24,000,000 fleet km. All prices below are illustrative USD inputs. Maintenance events at 240,000 km are included; initial factory-fitted parts are excluded. Replace the assumptions with matched fleet measurements and local quotes before making a purchase decision.

Reproducible arithmetic: Energy saving = 24,000,000 × (16.8 − 14.2) / 100 × $0.15 = $93,600. Net difference = $93,600 + $64,000 + $50,000 − $24,000 − $35,250 = $148,350. The collision assumption counts events and permits repeated events on one vehicle.

Downside test: Set both the energy advantage and rotor saving to zero while holding the other assumptions constant. The modeled saving falls to $4,750, before licenses, training, financing, downtime, tax, and other omitted costs. That narrow margin shows why the original favorable assumptions cannot justify an order. Rotor replacement remains condition-based in practice; zero replacements is not a maintenance recommendation.

Build low, central, and high cases using actual quotes and inspection records. Compare measured duty-cycle performance, approval readiness, service access, and parts support together. A cheaper assembly or an optimistic range claim cannot compensate for an unresolved approval or service dependency.

FAQ

Does every Chinese EV equipped with brake-by-wire have mechanical push-through backup?

Do not assume it. The exact architecture and failure concept must come from the offered variant's safety documentation and approval evidence. A hydraulic pedal fallback, where provided, may require greater effort and may not retain normal assistance or automatic functions. Electrical redundancy can address different failure cases.

Can our local workshop bleed a Chinese One-Box EV using manual pedal pumping?

The OEM procedure determines what is permitted for the particular operation. Some work requires a diagnostic routine to cycle internal circuits; ordinary fault-code access does not prove that capability. Obtain the exact instructions and demonstrate the required service functions before the fleet arrives.

What brake fluid must be used in a Chinese One-Box system?

Use the specification approved for the particular vehicle and service operation. Do not infer compatibility from the One-Box label or substitute DOT 5.1 for a specified low-viscosity fluid without OEM authorization. Obtain the fluid specification and service interval from the current workshop manual.

Do all Chinese domestic EVs change single-pedal behavior from January 1, 2026?

That conclusion does not follow from the headline implementation date. Section 6 explains the separate transition described in the government notice. Confirm the applicable vehicle approval history, controlling provisions, and delivered software rather than assuming every vehicle built in the same year behaves identically.

How much shorter is the stopping distance with One-Box EHB?

There is no universal meter advantage. Compare complete vehicle tests with matched speed, tires, road, load, temperature, and braking trigger. A supplier's time-to-lock figure is not interchangeable with pressure-rise time and cannot establish a fixed stopping-distance gain for another vehicle.

Can an importer replace a Bosch IPB unit with a Bethel WCBS unit?

Do not treat those assemblies as interchangeable. Use an OEM-authorized part or documented supersession with the required hydraulic, electrical, software, and approval compatibility. Confirm coding and calibration requirements before ordering a replacement.

How should recovery operators handle a flat low-voltage battery and locked EPB?

Follow the exact OEM recovery sheet and authorized transport arrangement. Power-support points and emergency-release methods vary. Do not use a generic actuator-removal or manual winding instruction; provide the recovery network with approved procedures before vehicles enter service.

13. Next Steps for a Vehicle Braking Specification RFQ

A useful RFQ links the offered vehicle configuration to destination approval evidence, workshop access, and parts commitments. Include:

• Target model, variant, quantity, production range, and destination country.
• Intended duty cycle and vehicle category.
• Known approval documents and unresolved homologation questions.
• Brake assembly identity, destination software, and required service capabilities.
• Local workshop arrangements, parts quotations, and requested warranty terms.

Contact China EV Exporter with your shortlist and destination requirements to request available supplier documentation and clarify open sourcing questions. Approval decisions remain with the relevant authority and appointed technical service; availability of specific reports and tooling must be confirmed for the offered vehicle. You can also explore the Chinese EV export catalog to prepare a shortlist.

14. Sources & References

Source check: November 7, 2026. The records below support the specific points identified; they do not verify an individual vehicle or constitute a complete review of destination law.

• SAMR/SAC: GB 21670-2025 official standard record — standard identity, publication date, and headline implementation date; full clauses and transitions must be read separately.
• Chongqing municipal government website: GB 21670-2025 implementation explanation, July 7, 2025 — public explanation of default accelerator-release behavior, transition dates, and regenerative stop-lamp signaling; the controlling standard takes precedence.
• UNECE: vehicle-regulation directory — discovery directory retained for locating UN R13-H and applicable amendments; not a specific regulation text, vehicle certificate, or independently checked current consolidation in this review.
• ISO 26262-1:2018: Road vehicles — Functional safety — Part 1: Vocabulary — exact identity and scope of the linked ISO record; does not establish product certification or destination approval.
• Bosch Mobility: integrated power brake — supplier description of an integrated EHB example and its stated time-to-lock and recuperation descriptors; does not substantiate model fitments, fleet savings, service parameters, or universal hardware benchmarks.

Review this guide before a new destination launch, a brake hardware or software change, or a relevant regulatory transition. Reconfirm source versions and procurement assumptions at the time of the order.