The Comfort Access System is made up of three parts: Comfort Entry (automated access control), Comfort Go (automated driver authorization), and Comfort Exit (automated exit).
Comfort Entry (unlocking)
The Comfort Entry allows passengers to enter the vehicle in a more relaxed manner while having the key fob in their pocket or purse.
- Pulling an outside door handle
- Pushing the tailgate or window (Touring) switch
When an outside door handle (TAG) is pressed and the boot lid/tailgate outside switch is pressed, a request for authentication of the vehicle’s identity is sent. Each TAG or bumper transmits the request through the relevant transmitter aerial.
In order to react to the request, a vehicle-specific identification must be within the aerial’s transmission range. Furthermore, the Car Access System (CAS) verifies that the identifier has car access authorization. If this is the case, the doors or boot lid/tailgate will be unlocked.
The subassembly that initiates the authentication process (outside door handle or boot lid/tailgate outside switch) determines which component is unlocked.
The luggage compartment aerial requires authentication of the vehicle’s identity when the luggage compartment is closed. The luggage compartment lid is opened again if an identifier in the luggage compartment responds and there is no other identifier outside the luggage compartment.
The luggage compartment lid remains closed if another identification is detected outside the luggage compartment. The identification in the luggage compartment has been disabled as a prospective transmitter for the vehicle’s next unlocking.
Comfort Go (engine start)
This function enables the car to start without inserting the key fob in the ignition lock.
The car interior aerials look for an identifier located in the vehicle when the start button and brake pedal are engaged. If a vehicle identifier is found inside the vehicle, the identifier is authenticated. The CAS allows the car to start if the identification has started authorization. The Comfort Access control unit turns on the aerials.
Comfort Exit (locking)
This function enables the locking of the car with a touch of a finger on the door handle.
By pressing an exterior door handle, the request to lock the vehicle is activated. If all of the doors are closed, the request will be processed. Then, using the outside aerials, an outdoor search for the identifier is conducted.
The vehicle is locked if identification is discovered outside the vehicle. This is followed by a search for an identifier in the passenger cabin to activate the lockout safety feature. The vehicle is unlocked again if the identity that was authenticated at the outside door handle is also detected in the passenger compartment.
Other vehicle identifiers are allowed to stay in the car. A related Check Control message is issued to alert the driver about this identifier.
Comfort Access Programming
The following assemblies must be initialized for the Comfort Access System.
- Comfort Access control unit
- Outside door handle electronics, driver’s door
- Outside door handle electronics, rear door on driver’s side
- Outside door handle electronics, passenger’s door
- Outside door handle electronics, rear door on passenger’s side
Initialization is required after replacing the Comfort Access control unit or an outside door handle. Switching terminal 0 to terminal R initiates the initialization process. When terminal R is turned on, the Car Access control unit sends the initialization to the Comfort Access control unit, which then sends it to the outside door handles.
As a result, when the comfort access components are replaced, the startup initialization will be completed automatically.
The programming/coding is only required as a part of software updates or when replacing the CA control unit from a different vehicle (Eg. from E90 to E93).
E90 Comfort Antennas Locations
The E90 Comfort Access system uses 8 antennas, with four of them being integrated into the door handles.
Door handle electronic module (S263) is integrated into the door handle.
Interior antenna center console (front) location.
Interior antenna center console (rear) location.
Inner antenna boot location.
Rear bumper antenna location.
E90 Comfort Access Module Location
The CA control unit is located in the luggage compartment at right (A215).
E90 Comfort Access Wiring
Pin assignments at plug connector X13354
| Pin | Type | Description /Signal type | Connection /Measuring notes |
| 1 | E/A | PA bus signal | Outer door handle electronic module, driver’s side |
| 2 | E/A | CAN bus low | K-CAN system bus |
| 3 | E | Signal, remote control receiver ON | Aerial diversity |
| 4 | E/A | PA bus signal | Outer door handle electronic module, passenger’s side |
| 5 | — | Not used | |
| 6 | A | Signal, identification-request | Inner antenna, center console, front |
| 7 | — | Not used | |
| 8 | A | Signal, identification-request | Interior antenna, center console, rear |
| 9 | — | Not used | |
| 10 | A | Signal, identification-request | Inner antenna, luggage compartment, rear |
| 11 | — | Not used | |
| 12 | — | Not used | |
| 13 | A | Signal, identification-request | Bumper aerial, rear |
| 14 | E | up to 03_2007 Supply, terminal 30 | Fuse F19 |
| 14 | E | from 2007_09 Supply, terminal 30G | Fuse F61 |
| 14 | E | from 2007_03 up to 2007_08 Supply, terminal 30G | Fuse F33 |
| 15 | E/A | CAN bus high | K-CAN system bus |
| 16 | M | Ground | Ground point |
| 17 | E/A | PA bus signal | PA bus connector |
| 18 | A | Signal, identification-request | Inner antenna, luggage compartment, rear |
| 19 | — | Not used | |
| 20 | A | Signal, identification-request | Inner antenna, center console, front |
| 21 | — | Not used | |
| 22 | A | Signal, identification-request | Interior antenna, center console, rear |
| 23 | — | Not used | |
| 24 | — | Not used | |
| 25 | A | Signal, identification-request | Bumper aerial, rear |
| 26 | — | Not used |
E90 Comfort Access Not Working [Troubleshooting]
The cause of not working comfort access in more than 90% of cases is a faulty outer door handle. If the comfort access fuse is blown, first check the door handles!
The door handle electronic modules share the power supply with the Comfort Access module. So, each of these five components can cause a short circuit and blown fuse in the junction box.
The power supply wire color is Red/Yellow and is powered by either terminal 30 (up to 02/2007) or via terminal 30G (from 03/2007).
The Comfort Access fuse is located in the junction box behind the glove box. Depending on the production date, the fuse is located at:
- Up to 02/2007 at No. 19 (7.5A)
- From 03/2007 up to 08/2007 at No. 33 (5A)
- From 09/2007 at No. 61 (5A)
Comfort Access Blown Fuse Troubleshooting
- Prepare at least 10 mini fuses (5A or 7.5A).
- Disconnect the door handle on the driver’s doors.
- Replace the fuse if necessary.
- If the fuse blows again, follow the same steps with the other handles.
- You’ve uncovered at least one cause if the fuse remains intact.
- Connect the other door handles one by one to see if they’re working properly.
Antenna Troubleshooting
If the door handles are working properly but you can’t lock/unlock the car just from one side, the failed antenna might be the cause.
If the problem is with the antenna not transmitting the signal to the CA control unit, the most likely cause is corroded or broken wires between CA control unit and antennas.
Comfort Access Communication Bus (K-TAGE) Troubleshooting
The Comfort Access sub-bus sends the status of the exterior door handles to the CAS and Comfort Access control unit. The state of the exterior door handles can be read out in the diagnosis system’s control unit operations.
If the status on a control unit can be read, the bus connection of the malfunctioning control unit must be verified. If the state of an outside door handle cannot be read, the bus line in the corresponding door or in this region must be verified.
The CAS serves as a connection point between the body CAN system and the CAN peripheral buses.
When troubleshooting the Comfort Access control unit, make sure the CAS is implementing the Comfort Access control unit’s diagnostic commands on the body CAN peripherals bus. Without the CAS function, the body CAN system, and the body CAN peripherals buses, a diagnosis on the Comfort Access control unit is impossible.
A bus breakdown between CAS and the Comfort Access sub-bus might cause problems throughout the bus system. The CAS contains a 1 kOhm bus terminating resistor, which is required for secure operation.
Comfort Access Door Handle Repair
E90 Comfort Access Key Battery
Unlike the standard E90 key fob, vehicles equipped with Comfort Access have different key fobs than regular CR2032. Depending on the usage and quality, they last for about two years before they need replacement.
Here’s a simple guide to replacing the battery.
