A driver walks up to the truck with both hands full, touches the door handle, and it unlocks. They climb in, press a button, and the engine starts. The key never leaves their pocket. That experience, familiar from the car park, is now specified on higher-trim commercial vehicles and on bus and coach programs where the cab feature list is a selling point. The module that makes it happen is the PEPS controller.
This guide is the version of the PEPS conversation we have with OEM engineering buyers during project scoping, written down. It assumes you know what a CAN bus and a BCM are, and that your program is weighing a keyless build, whether that is passive unlock on a higher-trim heavy truck, one-button start on a new-energy platform, or a full smart-key feature on a coach.
1. What a PEPS module does
PEPS stands for passive entry passive start. It is the controller that authenticates the smart-key fob without the driver pressing anything, works out where the fob is relative to the vehicle, and then authorises two things: unlocking the doors, and letting the start button crank the engine. Everything else in the keyless feature is built on those two authorisations.
The reason it is a dedicated job, rather than something the door-lock relay does on its own, is the security and localisation problem underneath it. The system has to prove the right key is present, prove it is in the right place (outside the door for entry, inside the cabin for start), and gate the engine behind a physical lock so a stolen vehicle cannot simply be driven away. On a commercial vehicle a PEPS controller is responsible for:
- Passive entry. Challenging the fob through a low-frequency antenna when the driver touches a door handle, and publishing an unlock-permitted message once the fob answers correctly.
- Smart-key authentication. Running the 125 kHz challenge and the 433.92 MHz coded response so only a paired fob is accepted, and holding the paired-key set in a learn-mode the program can update.
- In-cabin localisation. Using several antennas to tell whether the fob is outside a door or inside the cabin, which is what keeps the engine from starting while the key is still on the pavement.
- Push-to-start sequencing. Running the ACC, IGN and START outputs in order against a start-permission policy, with the brake or clutch interlock and the gear-in-park condition checked first.
- Steering-column lock gating. Driving an ESCL (electronic steering-column lock) so the column physically locks when no authorised key is present and releases only on an authenticated start.
- Alarm and reminder logic. Raising the key-left-in-cabin, key-not-detected and start-conditions-not-met warnings that a keyless feature needs to be safe to live with.
On the Youlai catalogue this role is filled two ways. The EBX‑964 PEPS core controller is a dedicated 24 V unit that owns the whole keyless stack on its own board, and the EBX‑2169 12 V BCM folds a full PEPS sub-system into a 178-pin body control module. Which one fits is the main sourcing decision, covered in section 4.
2. How passive entry and push-to-start work, step by step
A PEPS transaction is a challenge-and-response across two radio links. The low-frequency link goes out to the fob; the high-frequency link comes back. Understanding the sequence is what lets you write a sensible antenna plan and security policy later.
Step 1 — the driver touches the handle
The door-handle sense input — usually routed through the body BCM — tells the controller a hand is on a specific door. The PEPS module drives a 125 kHz challenge burst out of that door's low-frequency antenna. The burst carries the vehicle ID and a one-time session number, so a recording of an old challenge cannot be replayed.
Step 2 — the fob answers on the radio
The fob, carried in a pocket, demodulates the 125 kHz challenge, checks the vehicle ID against its paired ID, and transmits a 433.92 MHz response carrying the coded authentication payload. The PEPS controller's radio receiver captures that burst and authenticates it against the paired-key set. On a pass, the controller publishes an unlock-permitted message on CAN and the BCM drives the door-lock motor.
Step 3 — in-cabin localisation
Once the driver is seated, the controller runs a second challenge across several antennas to locate the fob. If the fob is inside the cabin, it asserts a fob-in-cabin state. This is the step that separates a full PEPS system from a simple passive unlock: the engine must not start unless the key is genuinely inside, not on the ground beside the door.
Step 4 — push-to-start
With the fob-in-cabin state set, the brake or clutch pedal pressed and the gear in neutral or park, a press on the start button runs the one-button-start sequencer. It releases the steering-column lock, drives ACC high, then IGN, then START to crank, and releases START on an engine-running confirmation. A second press shuts the engine down and re-locks the column. The whole policy — which conditions must pass before START is driven — is set by the program, not assumed by the box.
3. RKE, PKE and PEPS are three levels, not three products
The single most common confusion at the start of a keyless requirement is treating RKE, PKE and PEPS as alternatives to choose between. They are layers. Each adds capability to the one before it, and the cost and the antenna count climb with each step. Knowing which layer the program actually needs is what stops you paying for push-to-start on a base-trim build, or promising passive start when the requirement only funded passive unlock.
| Feature level | What the driver does | What it needs |
|---|---|---|
| RKE (remote keyless entry) | Presses lock / unlock on the fob. | A one-way 433.92 MHz receiver and a button fob. No low-frequency antennas. Often built into the BCM, as on the EBX‑2305. |
| PKE (passive keyless entry) | Touches the handle; doors unlock with the fob in a pocket. Engine still started with a key or switch. | Adds 125 kHz low-frequency antennas for the challenge, plus handle-sense inputs. The start column stays mechanical. |
| PEPS (passive entry passive start) | Touches the handle to enter, presses a button to start. Fob never leaves the pocket. | Adds in-cabin localisation, an ESCL, the push-button stack and the interlock policy. The full stack on the EBX‑964, or integrated on the EBX‑2169. |
A useful way to place a requirement: ask what the driver does to start the engine. If they still turn a key, you are at PKE or below, and you do not need an ESCL or a start sequencer. If they press a button and the fob stays in a pocket, you are at full PEPS, and the localisation, the steering-column lock and the interlock policy all come with it. Most disappointed keyless projects scoped PKE hardware against a PEPS expectation, and discovered the gap when the start button was added late.
4. Integrated or dedicated: where the PEPS function lives
Once the program is genuinely at full PEPS, the sourcing decision is whether the PEPS function lives inside the body control module or on a controller of its own. The answer is set mostly by the system voltage and by what the main BCM already does.
| Approach | Best fit | Reference module |
|---|---|---|
| Integrated — PEPS as a subset of a full-scope BCM | A 12 V passenger or higher-trim commercial program that wants one ECU to own body loads, the RKE receiver and the full PEPS stack, removing the BCM-to-PEPS CAN traffic and the inter-box harness. | EBX‑2169 — 12 V (9–16 VDC), ~50 functions across 7 groups, ~178 pins on 5 connectors, RF 433.92 MHz ASK/FSK. |
| Dedicated — a standalone PEPS core controller | A 24 V commercial program whose main BCM is a pure-logic or fuse-relay-integrated unit with no smart-key stack, so PEPS is added as a separate controller reporting to the BCM over CAN. | EBX‑964 — 24 V (18–32 VDC), 4 LF antenna pairs at 125 kHz, 433.92 MHz response, ESCL interface, push-button sequencer, IP53. |
The integrated route is cleaner when one ECU can reasonably own the whole body-electronics group, because every function that shares the board stops needing a CAN message and a connector to talk to its neighbour. The EBX-2169 is built for exactly this: a 12 V full-scope BCM that carries the lighting, wiper, central-locking and PEPS logic together, with the 433.92 MHz receiver on the same board and the low-frequency antennas routed in through one of its five connectors.
The dedicated route is the right one when the main BCM was never designed for a smart key, which is common on 24 V commercial platforms where the BCM is a rugged logic or fuse-relay unit such as the EBX‑954. Bolting PEPS into that BCM would mean redesigning it; adding a dedicated controller such as the EBX-964 keeps the existing BCM and lets the PEPS unit own the four-antenna challenge, the response demodulator, the ESCL gating and the start sequencer on its own board. It reports to the body BCM over a single CAN link, with the protocol confirmed per program.
5. Where PEPS shows up on commercial vehicles
Keyless entry started as a passenger-car feature, but the requirement now lands on several commercial-vehicle programs, each for a slightly different reason. The reason matters, because it changes which layer you need and where the antennas go.
- Higher-trim heavy trucks. On a long-haul tractor the keyless feature is a cab differentiator at the dealer level. A two-door cab needs fewer low-frequency antennas than a car, but the 24 V supply pushes most of these toward a dedicated controller alongside the existing rugged BCM.
- Bus and coach. A long body changes the localisation problem: the cabin is large, and the driver area has to be told apart from the passenger space. This is where the antenna count and placement need the most thought rather than a copied car layout.
- New-energy platforms. An electric or hybrid driveline adds a high-voltage power-up step to the start sequence, so the start authorisation has to coordinate with the powertrain side. The vehicle control unit owns that high-voltage sequencing; the PEPS controller authorises the request.
- Service and fleet integration. A keyless vehicle that also reports to a fleet back-end may accept a tightly scoped remote door-unlock through the telematics box, while the PEPS controller remains the part that authenticates the physical key at the vehicle.
The common thread is that a commercial PEPS layout is rarely a copied passenger design. The voltage, the cab size and the powertrain all change the antenna plan and the start policy, which is why the requirement is worth writing down before the hardware is fixed.
6. How to write a PEPS specification a supplier can quote
A PEPS requirement a supplier can quote against, rather than guess at, covers six things. Skipping any one of them is what turns a quick quote into a round of questions.
- System voltage. 12 or 24 V nominal and the tolerance band. This is the first fork: 12 V points toward an integrated-BCM path, 24 V commercial usually toward a dedicated controller.
- Feature level. RKE, PKE or full PEPS with push-to-start. State it plainly, because it decides whether you need an ESCL, a start sequencer and in-cabin localisation at all.
- LF antenna plan. How many 125 kHz antennas and where they mount, which sets the localisation zones — one per door is typical, with cabin-interior antennas added on a long body.
- Start and security policy. Whether an ESCL steering-column lock is required, the interlock conditions (brake or clutch pressed, gear in neutral or park), and the alarm and reminder set the program wants.
- Vehicle interface. The CAN protocol to the body BCM, how the door-handle and gear-position signals arrive, and whether the smart-key learn-mode is triggered from the BCM diagnostic tool or a service command.
- Destination market. The country or region the vehicles run in, which fixes the radio type approval the 433.92 MHz path has to carry. Settle it early; it is the section most often left blank.
The decision buyers leave until last and regret is the antenna plan in point three. The localisation quality — telling outside-the-door from inside-the-cabin — depends on it, and re-working the antenna layout after the harness is drawn is expensive. Decide it with the start policy, not after.
7. What to look for in a PEPS supplier
A PEPS module owns the security boundary of the vehicle and depends on a radio that is subject to per-market approval, so the supplier questions that matter are about capability and honesty, not headline price.
- Quality system in hand. Ask for the IATF 16949 certificate and what the PPAP package contains. Youlai manufactures under IATF 16949 with a PPAP package on program handoff. Treat any verbal "automotive grade" claim without a certificate number as marketing.
- Smart-key and localisation experience. The four-antenna 125 kHz challenge, the in-cabin localisation and the ESCL handshake are not generic embedded work. A supplier that has shipped PEPS should discuss the antenna plan and the start-permission policy concretely rather than promising a blanket keyless feature.
- Pairing and learn-mode. Ask how a new fob is paired in production and in service. A controller with an on-board learn-mode, triggered from the BCM diagnostic tool or a service command, avoids needing a PEPS-specific programmer in the field.
- EMC and environmental capability. A unit running both a 125 kHz transmitter and a 433.92 MHz receiver is both an EMC source and a victim. Confirm in-house EMC pre-compliance and environmental testing rather than outsourced-only validation. Youlai validates in an in-house environmental laboratory with EMC pre-compliance equipment.
- Region-specific approvals. The radio type approval for the destination market is available upon project requirement, confirmed per market on a project basis rather than blanket-claimed across the catalogue. An honest supplier separates what it holds in hand from what it runs per project.
Questions you will be asked at RFQ stage
- MOQ and samples. A configurable variant of an existing EBX platform can usually move to samples quickly; a fob protocol or antenna plan unique to your program follows the firmware and approval timeline. Sample quantities are agreed per program.
- Lead time. Driven mostly by the destination-market radio approval and the smart-key pairing integration, not by the hardware build itself.
- PPAP timeline. The IATF 16949 PPAP package (drawings, BOM, control plan, FMEA, dimensional and test reports) is prepared on program handoff.
- Customisation scope. Variants on an existing EBX platform — antenna count, CAN matrix, ESCL interface, start policy, connector — are routine, not an exception.
If you are scoping a keyless system, the most useful things to bring to a first conversation are your system voltage and your feature level from section 6 — whether you need full PEPS or only passive unlock, and how many antennas the cab calls for. That lets us map your requirement onto the EBX‑2169 integrated BCM or the EBX‑964 dedicated controller, or tell you honestly where a custom variant is needed. For how PEPS sits among the BCM, VCU, PMU and gateway, the Smart Control Modules technical guide covers the full module stack.
For drawings, an antenna-plan and start-policy review or a sample request against your vehicle program, please use the contact page or message +86 134 6767 4786 on WhatsApp. Typical reply within 24 hours during China business hours (UTC+8).