Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Passive Entry: Notes
The graphic below shows the functional principle of "Passive Entry".
| Index | Explanation |
|---|---|
| 1 | Outside door handle electronics module (TAGE) |
| 2 | TAGE request to the CAS |
| 3 | Prompt about Comfort Access antenna |
| 4 | Comfort Access antenna |
| 5 | ID transmitter |
| 6 | Rear window antenna |
| 7 | Remote control receiver in the diversity module |
| 8 | Car Access System 4 (CAS 4) |
| LIN-Bus | Local Interconnect Network bus |
| f1 | Low frequency in the kHz range |
| f2 | High frequency in the MHz range |
| K-CAN2 | Body CAN2 |
| CA/FBD | Comfort Access/remote control services |
Passive Entry enables access to the vehicle without the ID transmitter being actively operated.
For example, if the outside door handle is pulled, this triggers a pulse in the sensor. The outside door handle electronics analyze the sensor and inform the Car Access System that vehicle access is requested.
The Car Access System prompts the ID transmitter to identify report to the vehicle. For this, a low-frequency signal is emitted by Comfort Access via the antennas. Transmission is via the 125 kHz antennas.
The 125-kHz signal serves only to wake the ID transmitter. The ID transmitter responds with its transmission frequency. Subsequent communication is now bi-directional, i.e. in two directions. The Car Access System sends or receives all further information via the LIN bus.
The remote control receiver is equipped with both a receiver unit and a transmitter unit. It establishes the connection with the ID transmitter via the rear-window antenna. For that reason, only the high frequency range is now used.
Bi-directional communication has the advantage that data can be requested from or sent to the ID transmitter. The Car Access System has sole responsibility for this communication.
If the ID transmitter is able to be authenticated, the Car Access System initiate the request, e.g. unlocking the vehicle. The junction box electronics execute the unlocking.
The transmission frequency of the ID transmitter varies for the US is 315MHz.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.