Hyundai Sonata LF Quiz
Body Electrical System

Description and Operation

In this manual: Body Electrical System
General Information — 9Engine Mechanical System — 90Engine Electrical System — 58Emission Control System — 24Engine Control System/Fuel System — 114Drive Shaft and Axle — 15Suspension System — 35Steering — 19Restraints — 50Brake System — 54Body (Interior and Exterior) — 213Body Electrical System — 241Heating, Ventilation, and Air Conditioning — 56DCT (Dual Clutch Transmission) System — 52
30steps
~180min
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Description

The SMART KEY system allows the user to access and operate the vehicle in a very convenient way. No traditional key or remote control is required to access the vehicle. The user carries the SMART KEY FOB, which does not require any conscious action by the user (such as pressing an RKE button). SMART KEY system is activated by pressing the button on the door handle. After activation, the vehicle sends a request within a limited range. If the SMART KEY FOB receives this request, it automatically sends a response to the vehicle. The system then decides whether to perform a certain action (unlock, lock...) or remain inactive. Again, communication between the vehicle and the SMART KEY FOB is required before any action is performed. The system offers the following functions:
  • Passive Unlock via 4 Doors
  • Passive Lock via 4 Doors
  • Passive Start
  • Passive Trunk Access via Trunk Lid Switch
  • A maximum of 2 fobs can be processed by the system
  • Immobilizer backup antenna driver is integrated in the SSB for TP authentication (i.e., in idle mode)
  • Communication with Engine Management System
  • Communication with SRX
  • LF-RF Communication
  1. Passive Unlock. The system allows the user to access (unlock) the vehicle without performing any action with the SMART KEY fob.
  2. Passive Lock. The system allows the user to lock the vehicle by pressing the button on the door handle with the SMART KEY fob.
  3. Start Button. The system allows the user to switch power modes (OFF, ACC, ON) and to start and stop the vehicle engine without performing any action with the SMART KEY fob. Refer to Engine Start System Specification.
  4. LIMP HOME Mode. In addition, the system offers a so-called "limp home mode", meaning the user can operate all vehicle functions by pressing the key in the SSB.
SMART KEY Control Unit (SMK ECU) The SMK ECU controls all functions related to Passive Unlock, Passive Lock and Passive Engine Start Authorization. It reads inputs (door handle button, Start Stop Button (SSB), PARK position switch), controls outputs (such as exterior and interior antennas), and exchanges data via CAN, as well as a single-wire interface with other vehicle devices. To communicate with the SMART KEY FOB, the SMK ECU generates a request (challenge) as an encoded and modulated 125 kHz signal output via the inductive antenna, and receives the SMART KEY FOB response via the external RF receiver. The main functional blocks of the SMK ECU are:
  • Power Supply
  • Flash Memory Microcontroller
  • Single-Wire Interface to SRX
  • Single-Wire Interface to EMS
  • Input Stage
  • LF Antenna Amplifier/Driver
  • CAN Communication with BCM
LF Antenna Amplifier/Driver generates a sinusoidal 125 kHz carrier signal, which is distributed to the different antennas. SMART KEY FOB The system supports up to 2 SMART KEY FOBs. Main functions of the SMART KEY FOB:
  • Passive Function: receives the LF call and automatically sends an RF response.
  • Classic RKE function by means of up to 4 buttons.
  • Transponder operation in case of battery discharge or communication failure.
Antennas
  1. LF Transmitting Antennas: Inductive antennas inside and on the vehicle are used to convert the current supplied by the SMK ECU antenna driver into a 125 (or 134.2) kHz magnetic field, which is the carrier for the SMART KEY test. Three antennas cover the exterior of the vehicle: two antennas in the door handles (DS and PS) cover the area around the doors; one antenna in the rear bumper covers the area around the trunk or liftgate. Up to three antennas cover the vehicle interior and the trunk or liftgate compartment: two in the cabin and one in the luggage compartment or trunk.
  2. Bidirectional Immobilizer Antenna (for Limp Home): The backup immobilizer antenna is used to send and receive data: it radiates a magnetic field (125 - 135 kHz call) and receives changes in field strength (transponder response).
  3. Receiver. The SMART KEY fob response is received through the RF receiver.
Door Handle The front door handles of both doors (driver/passenger door) are equipped with LF transmitting antennas to emit 125 kHz signals. The front door handles are also equipped with push buttons. Pressing the button on the door handle serves as a trigger, indicating the user's intention to unlock or lock the vehicle. The buttons are installed on the front doors, built into the door handles. Another button is installed on the trunk lid or tailgate.

Operation

Passive Functions The system allows the user to access the vehicle without performing any action (such as pressing an RKE button) using the SMART KEY FOB. It is sufficient for a valid SMART KEY FOB to be within a specified and limited range relative to the vehicle. Thus, the system is capable of detecting and authenticating the SMART KEY FOB within the ranges shown below.

Operating Range

The SMART KEY FOB receives and interprets the challenge sent from the vehicle through the exterior antennas within a free-space radius of at least 0.7 m around the exterior antennas built into the door handle; refer to the illustration below. Trunk or liftgate access range is also at least 0.7 m from the antenna location. Passive Entry (Passive Unlock): Press the door handle button when all doors are locked to indicate the operator's intent to access the vehicle, which activates the system to unlock. Passive Lock (Exit): Pressing one of the door handle buttons when one of the following conditions is met indicates the operator's intent to lock the vehicle, which activates the locking system.
  • At least one door is open and the two-step timer is not running, or
  • The two-step timer is running and one of the buttons other than the front left one is activated.
Passive Trunk Warning (Sedan Only): Whenever the trunk is closed, the SMK ECU uses an appropriate search strategy to avoid the trunk buzzer warning when the FOB is outside the vehicle. The SMK then searches for the SMART KEY FOB inside the trunk compartment. If a valid SMART KEY FOB is detected in the trunk, the SMK ECU activates the SMK exterior buzzer (TBD) to inform the user that the trunk has been closed with the FOB inside. The SMK will send a trunk reopen command to the BCM if the trunk reopen (BK) bit is set. A "valid" SMART KEY FOB means any SMART KEY FOB belonging to the vehicle, even if it is DEACTIVATED.
  • A blind spot in the trunk, similar to any RF interference, may result in no trunk warning. Due to the antenna penetrating the bumper into the trunk area, the lid may open without the ID device being outside.
  • A blind spot in the trunk, similar to any RF interference, may result in no trunk warning.
Smart Trunk [Vehicle Condition]: Smart Trunk Setting When a user with a valid smart key is within the vicinity of the rear bumper (within the LF antenna range) for more than 3 seconds, the trunk opens.
The function is set in User Settings Mode (USM) in the cluster.
  1. The rear bumper antenna detects a valid SMART KEY nearby.
  2. When a valid SMART KEY enters the range of the rear bumper antenna, the warning buzzer and hazard lamps activate once to confirm detection.
    • The SMART KEY ECU can detect a SMART KEY within 0.7–1 m of the rear bumper.
    • If the SMART KEY remains within the detection range, the warning buzzer and hazard lamps activate once per second for the entire time the SMART KEY stays in the detection zone.
  3. If the SMART KEY remains within the rear bumper zone (antenna range) for more than 3 seconds, the buzzer and hazard lamps activate 2 times and the trunk opens.
  4. Preconditions: All terminals OFF, at least one door open, and lock status not locked. Checked by the SMK periodically every 100 ms while CAN/LIN is active.
  5. Event: Status of at least one door handle has changed from unlocked to locked.
  6. SMK Actions:
    A. IF the FOB is not active, the SMK searches for FOBs inside the vehicle cabin. Use the same LF strategy as for the ID OUT warning (registration only, no authentication).
    B. IF the FOB is ACTIVE, the SMK searches for a valid TP.
    If no fob or TP is detected, no action is required. If any valid fob or valid TP is detected, the SMK unlocks the vehicle by transmitting the Key Unlock CAN message with the fob number. If any valid fob is detected, the SMK unlocks the vehicle by transmitting the Key Unlock Reminder CAN/LIN message with the fob number.
  7. Preconditions: All terminals OFF, any door (including trunk) open, and no FOB-IN and lock status (periodically checked by the SMK every 100 ms while CAN/LIN is active).
  8. Vehicle action: Closing the last door or trunk with the handles locked or while locking is in progress.
  9. SMK actions: 500 ms after closing, if all doors are locked, then:
    A. IF the FOB is not active, the SMK searches for FOBs inside the vehicle cabin. Use the same LF strategy as for the ID OUT warning (registration only, no authentication).
    B. IF the FOB is ACTIVE, the SMK searches for a valid TP.
    If no FOB is found, no action is required. If any valid FOB or valid TP is found, the SMK sends a CAN unlock command and activates the additional buzzer warning. If a valid FOB is found, the SMK sends a CAN/LIN unlock command and activates the additional buzzer warning.
  10. If the final state is ACC or IGN, all doors are closed, and the user initiates SMK locking, the search starts outside the vehicle from the trigger side.
  11. If no valid FOB is found, no action is required, but if a valid FOB is found, the buzzer warning must be activated.
  12. If "b_Trunk Option == On" and "b_Trunk Lock Unlock Option == On", the lock warning treats the trunk lid as a door, and the trunk lock unlock handle as a door unlock switch.
  13. If the terminal state is OFF and not all doors are closed, and the user initiates SMK locking, the search starts outside the vehicle from the trigger side.
  14. If no valid FOB is found, no action is required, but if a valid FOB is found, the buzzer warning must be activated.
  15. If "b_Trunk Option == On" and "b_Trunk Lock Unlock Option == On", the lock warning treats the trunk lid as a door, and the trunk lock unlock handle as a door unlock switch.
  16. If the terminal state is OFF, ATWS is considered disarmed, all doors are closed, and the user activates SMK locking, the search starts inside the vehicle cabin.
  17. If a valid FOB is not found, the SMK locking search is started, but if a valid FOB is found, the buzzer warning must sound.
  18. If "b_Trunk Option == On" and "b_Trunk Lock Unlock Option == On", the lock warning treats the trunk lid as a door, and the trunk lock unlock handle as a door unlock switch.
  19. If the final state is ACC or IGN and vehicle speed is less than 3 km/h, a periodic search (every 3 s) is performed inside the vehicle to confirm that a valid FOB is still in the vehicle.
  20. If a valid FOB is not found, the warning is triggered, but if a valid FOB is found, no action is triggered.
SMART KEY Reminder 1. SMART KEY Reminder 2. SMART KEY Door Lock Warning. Door Lock Warning 1. Door Lock Warning 2. Door Lock Warning 3. Smartkey Indicator Warning. Fail-Safe Functions (Limp Home Backup). If the SMART KEY fob battery is discharged or communication is disrupted, the following functions are available:
  • Unlocking/locking doors or trunk (or rear door depending on vehicle equipment): with mechanical key
User Information Functions

No ID Warning

  1. Preconditions:
    A. (ACC or IGN1) & (any door open or trunk open)
  2. Event: Last open door closed
  3. SMK action: SMK searches for the SMART KEY FOB inside the cabin.
    A. If a valid SMART KEY FOB is not found, the SMK activates the external buzzer and sends an ID OUT warning via CAN (external buzzer warning and internal buzzer).
    B. If a door is opened and closed again during ignition on/off while a valid FOB is inside, the SMK re-enables authentication and stops the warning. If the terminal is in ACC mode, the SMK must turn on the immobilizer lamp.
If there is an LF fault (LF overheating or LF antenna failure), the system behaves the same as when no FOB is found.
FOB Low Battery Detection: To determine the FOB battery status, a battery voltage measurement and low-voltage detection strategy is implemented in the FOB. Battery voltage measurement is performed when the FOB button is pressed or an LF measurement command is received. Registration Description: This section describes the registration procedure for the SMK and FOBs. A diagnostic tool connection is required to register the SMK and FOBs. Registration Mode: In any mode, the registration process is controlled by the SMK. Before starting the registration service, the Fob-In signal must be active and the vehicle secret code (called the PIN code) must be known. Registration Mode: This mode is used by dealers to replace the SMK and/or key set, or to register additional keys for an existing system. This means the system has already been registered with a specific PIN code. The PIN code is fixed for the entire service life of the vehicle, so the same PIN code must be used in this mode. Otherwise, registration will fail. Registration Mode Procedure Description (Step by Step) Purpose: Key registration procedure at the service station. Initial Condition:
  • SMK replacement: SMK not learned, and SMART FOB already learned with the same PIN code
  • Learning additional or new keys: SMK already learned with the same PIN code
Starting After Replacement (Initial Start). Starting is possible in the following sequence after replacing the new SMART KEY or fob.
  • This is for starting from the virgin state
  • All related parts in initial state (smart key, ECM)
  • Depress the brake pedal in P or N range
  • Press the start button once with the virgin smart key.

Test yourself

A quick Hyundai Sonata LF quiz: every answer comes with an explanation and a link to the manual page.