Steering Wheel Heater (LRH), Function - GF46.11-P-0001KJE
MODEL 453.091/391/491
with CODE 443 (Steering wheel heater)
with CODE U14 (Climate package)
Function requirements, general
- No undervoltage or overvoltage (consumer shutoff not active)
- Circuit 15R ON (for manual activation)
The climate control unit (N22/1) receives the circuit status of circuit 15R ON from the vehicle interior fuse and relay module via a direct electrical line. To do so, the ignition lock switches a relay in the vehicle interior fuse and relay module, which connects the power supply to climate control unit.
Steering wheel heater, general
It is possible to heat the steering wheel using the steering wheel heater. The steering wheel heater is switched on via left front seat, seat heater switch (S51/1) (left-hand drive vehicle) or right front seat, seat heater switch (S51/2) (right-hand drive vehicle) along with the seat heater of the driver's seat and activated by the climate control unit. The temperature control is regulated by steering wheel heater control electronics (R22/4n1) in the steering wheel. Via the steering wheel heater temperature sensor (R22/4b1) integrated in the steering wheel, the steering wheel heater control electronics determine the steering wheel temperature and actuate the steering wheel heater accordingly. The steering wheel heater can also be activated by climate control unit with circuit 15R OFF during preheating of the vehicle.
The steering wheel heater control electronics actuate the following heating elements:
- Steering wheel heater heating element (R22/4r1)
The other function sequences are described using a left-hand drive vehicle as an example. Accordingly, for right-hand drive vehicles, the specifications "left front seat" apply for the right front seat.
The steering wheel heater heating element and the steering wheel heater temperature sensor are part of the steering wheel and cannot be replaced separately.
The steering wheel heater receives the supply voltage for the steering wheel heater heating element via steering wheel heater relay (F2k7).
The steering wheel heater relay is located at the vehicle interior fuse and relay module and is actuated by the climate control unit as soon as the steering wheel heater at the left front seat heater switch is turned on. It then connects the power supply (circuit 30g) via steering wheel clock spring contact (A45/1) to steering wheel heater control electronics. Switching the steering wheel heater on manually is only possible when the ignition is switched on and the steering wheel heater is automatically switched off as soon as the ignition is switched off (circuit 15R OFF).
The steering wheel heater function comprises the following subfunctions:
- Function sequence for manually switching on/off
- Function sequence for automatic switch off
Function sequence for manually switching on/off
Switching on and off takes place via left front seat heater switch. The status of left front seat heater switch is read in via a direct electrical line by the climate control unit. If the climate control unit receives the signal from the front seat heater switch, then it activates the steering wheel heater by connecting voltage to steering wheel heater control electronics via steering wheel heater relay at the same time as the seat heater. The steering wheel heater control electronics then actuate the steering wheel heater heating element. If the steering wheel heater was activated along with the seat heater, this is indicated via the status LED in the left front seat heater switch. The climate control unit switches off power supply to the steering wheel heater as soon as it recognizes a status change of the left front seat heater switch, at which point is deactivates the status indication.
Function sequence for automatic switch on/off
The automatic switch on/off function is implemented by the climate control unit or the steering wheel heater control electronics and is divided into the following subfunctions:
- Automatic timer shutoff function
- Function sequence for automatic switch-on while preheating
- Function sequence for immediate activation of preheating via vehicle homepage
- Automatic shutoff in case of overtemperature, function
- Automatic shutoff via energy management function
Automatic timer shutoff function
If the steering wheel heater is active for a certain period of time, then the climate control unit independently cuts off the power supply to the steering wheel heater control electronics and thus the steering wheel heater. The time period after which the steering wheel heater gets deactivated by the climate control unit varies and is individually adjusted as required and as per the interior temperature of the climate control unit. The steering wheel heater can, however, be switched on again with the driver-side seat heater.
Function sequence for automatic switch-on while preheating Additional function requirements:
- Charge level (residual capacity) of high-voltage battery min. 45 %
- Charging cable connected to vehicle and vehicle in state of charge
Automatic switch-on while preheating is divided into the following subfunctions:
- Preheating at the desired switch-on time (time) via submenu in instrument cluster
- Preheating at the desired switch-on time (time) via vehicle homepage Preheating at the desired switch-on time (time) via submenu in instrument cluster
Via left multifunction steering wheel button group (S110) and menu "Preentry climate control and charge" in the multifunction display (A1 p13) of the instrument cluster (A1), two points of time in the day can be preset for preheating of the vehicle, at which the vehicle should be preheated. The point of time at which preheating of the vehicle starts is calculated by the climate control unit as per the interior temperature and as required. At normal outside temperatures, it starts at approx. 10 to 20 min before the preset point of time. At low outside temperatures, preheating of the vehicle begins much earlier. Preheating of the seat heater and the steering wheel heater themselves begins max. 10 min before the determined time at which the vehicle should be preheated.
For this, the instrument cluster sends the preset points of time to the center SAM control unit (N10/10) and additionally to the electric drive control unit (N127) via interior CAN (CAN B). At the desired switch-on time, the center SAM control unit, which is the master for timer control, then sends the request for preheating the vehicle to the electric drive control unit. The electric drive control unit checks the specified requirements: battery capacity status at least 45 %, and charging capacity. This information is sent to the electric drive control unit by the battery management system control unit (N82/2) via electric drive CAN (CAN EL). If the specified requirements are fulfilled, it sends the request for preheating the vehicle by means of the CAN message "PreHeatingActivation" to the climate control unit via interior CAN. The climate control unit triggers the preheating of the vehicle and thus also switching on of the steering wheel heater. If the preset time for preheating is exceeded, then preheating is switched off again automatically after a certain period of time as long as the vehicle is not unlocked or started. Preheating of the vehicle is indicated by means of a symbol in the multifunction display of the instrument cluster. For this, the electric drive control unit sends the CAN message "PreHeatingStateDisplay" to the instrument cluster via interior CAN. The LED status indications in the front seat heater switches are not turned on during preheating.
Preheating at the desired switch-on time (time) via vehicle homepage
The following abbreviation is used in the text below: Global System Mobile (GSM).
Using a smartphone or PC, a menu can be called up via "smart me" and the vehicle homepage for preheating of the vehicle, in which two points of time can be preset or activated in the telematics services communications module (N112/2) before which the vehicle should be preheated. For preheating, the telematics services communications module receives a GSM signal via the integrated GSM antenna. The telematics services communications module sends the preset points of time to the center SAM control unit and the electric drive control unit via interior CAN. At the right time before the desired switch-on time, the center SAM control unit, which is the master for timer control, then sends the request for preheating the vehicle to the electric drive control unit. After checking the specified requirements (sufficient battery capacity available), the electric drive control unit sends the request for preheating the vehicle by means of the CAN message "PreHeatingActivation" to the climate control unit via interior CAN. The climate control unit then triggers the preheating of the vehicle and thus also switching on of the steering wheel heater. The seat heater and steering wheel heater are switched on approx. 10 min before the desired time. After the preset time for preheating is exceeded, preheating is switched off automatically after approx. 15 min as long as the vehicle is not unlocked or started. Preheating status of the vehicle is indicated by means of a symbol in the multifunction display of the instrument cluster. Preheating status is also displayed on the vehicle homepage; for this, the electric drive control unit sends the CAN message "PreHeatingStateDisplay" to the telematics services communications module. Via the integrated GSM antenna and a GSM signal, the telematics services communications module transmits the status to the vehicle homepage, which can be called up using a smartphone or PC.
Function sequence for immediate activation of preheating via vehicle homepage
Additional function requirements:
- Charge level (residual capacity) of high-voltage battery min. 45 %
Preheating can also be immediately switched on sporadically upon the driver's wish via "smart me" and the vehicle homepage using a smartphone or PC. For preheating of the vehicle, the telematics services communications module receives a GSM signal via the integrated GSM antenna. It then sends the request for preheating the vehicle to the center SAM control unit via interior CAN (CAN B). The center SAM control unit sends the request for preheating the vehicle to the electric drive control unit via interior CAN. After checking the specified requirements (sufficient battery capacity available), the electric drive control unit sends this request to the climate control unit via interior CAN. The climate control unit then triggers the preheating of the vehicle and thus also switching on of the seat heater and the steering wheel heater. After a certain preheating time (approx. 5 min) the seat heater, with the steering wheel heater, is switched off again. Preheating of the vehicle and seat heater is indicated in the multifunction display of the instrument cluster. Preheating status is also displayed on the vehicle homepage; for this, the electric drive control unit sends the CAN message "PreHeatingStateDisplay" to the telematics services communications module.
Automatic shutoff in case of overtemperature, function
If the steering wheel heater control electronics detect overtemperature via the steering wheel heater temperature sensor integrated in the steering wheel heater, then it switches off voltage supply to the steering wheel heater heating element. If the steering wheel temperature has dropped to a certain specified value, the voltage supply is switched on again. The LED status indication in the left front seat heater switch remains on during this process. The steering wheel heater heating element consists of a PTC thermistor cable (positive temperature coefficient (PTC)), which means that the power consumption decreases with increasing heating element temperature. The steering wheel heater control electronics in the steering wheel regulate the temperature to approx. 35°C.
Automatic shutoff via energy management function
The energy management can cut off various electrical consumers if necessary; for example, for increasing the range. For this, the electric drive control unit sends this request via interior CAN to the climate control unit, which deactivates the steering wheel heater.
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