GF46.11-P-1001M Switching Steering Wheel Heater (LRH) on/Off, Function

GF46.11-P-1001M Switching steering wheel heater (LRH) on/off, function
- with CODE (443) Steering wheel heater

15.03.07 The document has been updated to this date and will no longer be subject to revision.

Function requirements:
^ 15R On or 15 ON from EIS control module (N73) via CAN class B.

Switch on steering wheel heater
The position of the steering wheel heater switch (S59/1s2) is read out by the electronics in the steering column module (N80) and placed on the CAN class B.

As long as the steering wheel heater switch (S59/1s2) is operated (turned upwards), the operated position is sent cyclically. The cycle time is t = 100 ms.

The center position of the steering wheel heater switch (S59/1s2) is not sent by the steering column module (N80).

The center position is recognized if within t = 3 cycles no message is sent from the steering wheel heater switch (S59/1s2) or if the two corresponding bits for the rotary operation of the steering wheel heater switch (S59/1s2) are not set.

The message for the actuation of the function LED (red) is placed cyclically on the CAN class B by the DC/DC converter control module (N99) and is read out by the steering column module (N80). This actuates the function LED integrated in the steering wheel heater switch (S59/1s2).

If the DC/DC converter control module (N99) receives the command "Steering wheel heating", the steering wheel heater electronics (A74) fitted in the steering wheel are supplied with voltage which energizes the heating coil (R22/40).

In addition the steering wheel heater electronics (A74) measures the surface temperature of the steering wheel rim via a temperature sensor integrated in the steering wheel. If the temperature rises to above 28 degrees C, the energizing of the heating coil (R22/4r1) is interrupted. If the temperature drops below 24 degrees C (during the control) or below 26 degrees C (during a hot start), the heating coil (R22/4r1) is energized again.

The interior temperature is reported by the overhead control panel control module (N70) via the CAN class B and is evaluated in the DC/DC converter control module (N99) in order to protect the heater coil (R22/40). At interior temperatures above 30 degrees C the steering wheel heater is switched off in order to prevent the heating coil (R22/4r1) from overheating.

Initially the steering wheel heater is operated with maximum power (voltage supply 48 V) in order to achieve adequate heating up of the steering wheel. After t = 7 minutes the steering wheel heater is operated with reduced power (voltage supply 42 V) in order to prevent the heating coil (R22/4r1) from overheating.

Only a limited current of approx. 2 A can be supplied via the heating coil (R22/4r1). The voltage transformation is necessary in order to realize steering wheel heating with a power of approx. 100 W.

Finishing steering wheel heating
The heating mode of the steering wheel heater is finished manually by turning the steering wheel heater switch (S59/1s2) downwards.

The steering wheel heater is switched off automatically when a continuous heating mode over a period of 24 minutes is detected by the DC/DC converter control module (N99) or one of the following shutoff conditions occurs:

^ Switching off after ignition circuit 15R OFF
The steering wheel heater also switches off once circuit 15R is switched off. However, the time control continues on for t = 5 minutes for as long as circuit 15 is "ON". If circuit 15R is switched on again, the steering wheel heater is switched on again with the output voltage existing before it was switched off. The timer (t = 7 minutes) for the reduced heating voltage of 42 V is not reset.

^ Switching off in the event of undervoltage (less than 11 V) or overvoltage (greater than 16 V)
The steering wheel heater is switched off if undervoltage or overvoltage is detected. The function LED flashes. The timer (t = 7 minutes) for the reduced heating voltage of 42 V is not reset. If the voltage is in the normal range again, the steering wheel heater switches on again with the output voltage existing before it was switched off. The function LED comes on again accordingly.

^ Switching off while the engine is being started
The steering wheel heater is switched off while starting the engine. The function LED remains switched on. The timer (t = 7 minutes) for the reduced heating voltage of 42 V is not reset. Once the engine has been started the steering wheel heater switches on again with the output voltage existing before it was switched off.

^ Switching off when steering column adjustment is active
The steering wheel heater is switched off during active steering column adjustment. The function display remains switched on. The timer (t = 7 minutes) for the reduced heating voltage of 42 V is not reset. Once the steering column is adjusted, the steering wheel heater only switches on again after t = 5 seconds with the output voltage existing before it was switched off. However, if the timer (t = 7 minutes) for the reduced heating voltage of 42 V has come to an end, the system switches to the output voltage of 42 V with a stop condition following it.

^ Switching off if the DC/DC converter control module overheats (N99)
The DC/DC converter control module (N99) has its own safety shutoff, the steering wheel heater being switched off at a temperature of > 95 degrees C in the DC/DC converter control module (N99).