Steering wheel heater (LRH), function

P46.11-2146-81

P46.11-A000-81

Function requirements, general

 Circuit 15R ON

 Interior temperature below 30 °C

 The electronic ignition lock control unit transmits the circuit status of circuit 15 to the steering wheel electronics via the suspension FlexRay, steering column tube module control unit and the steering LIN (model 205 up to model year 2019, model 253 up to model year 2020) or the steering wheel CAN (model 205 as of model year 2019, model 253 as of model year 2020).

 The climate control control unit transmits the vehicle interior temperature to the steering wheel electronics via the interior CAN, electronic ignition lock control unit, suspension FlexRay, steering column tube module control unit and steering LIN (model 205 up to model year 2019, model 253 up to model year 2020) or steering wheel CAN (model 205 as of model year 2019, model 253 as of model year 2020).

Steering wheel heater, general

The steering wheel heater heats the steering wheel rim of the steering wheel.

In model 205 with code 577 (Remote activation of heating and ventilation systems) and in plug-in hybrid vehicles, the steering wheel heater can be switched on via the pre-entry climate control for a maximum of 60 s (after the vehicle is unlocked). The steering wheel is thereby heated prior to driving off.

Switch steering wheel heater on/off

The steering wheel heater is operated using the steering wheel heater switch in the steering column adjustment and steering wheel heater switch. Turning the steering wheel heater switch on the steering column adjustment and the steering wheel heater switch switches the steering wheel heater on or off. The steering column tube module control unit reads in the status of the steering wheel heater switch directly.

In model 253 as of model year 2020, the steering wheel heater can also be operated via the voice control system (VCS). In this case, the head unit transmits the corresponding request via the user interface CAN, electronic ignition lock control unit and suspension FlexRay to the steering column tube module control unit.

The steering column tube module control unit transmits the status of the steering wheel heater switch or the request via the VCS (model 253, as of model year 2020) to the steering wheel electronics via the steering LIN (model 205 up to model year 2019, model 253 up to model year 2020) or the steering wheel CAN (model 205 as of model year 2019, model 253 as of model year 2020). The steering wheel electronics then actuate the steering wheel heater heating element in the steering wheel rim or cancel the actuation.

The surface temperature of the steering wheel rim is detected by the heating element temperature sensor. The steering wheel electronics read in the signals of the heating element temperature sensor directly and regulate the surface temperature of the steering wheel rim to approx. 35 °C.

The steering wheel electronics transmit the status of the steering wheel heater via the steering LIN (model 205 up to model year 2019, model 253 up to model year 2020) or the steering wheel CAN (model 205 as of model year 2019, model 253 as of model year 2020) to the steering column tube module control unit. When the steering wheel heater is switched on, the steering column tube module control unit actuates the steering wheel heater indicator lamp in the steering wheel heater switch.

Automatic steering wheel heater switch off

The steering wheel heater is switched off automatically after 15 min. The timer control is stored in the steering wheel electronics and can be parameterized with the diagnostic tester.

Other shutoff criteria:

 Shut-off in the event of a hardware defect

If actuation of the steering wheel heater is detected without an existing request or function requirement, the steering wheel electronics switch off the steering wheel heater and file a fault message in the fault memory.

 Switch-off in the event of overtemperature

If the vehicle interior temperature rises above 30 °C, the steering wheel electronics switches off the steering wheel heater. The steering wheel heater indicator lamp remains on. If the vehicle interior temperature drops below the cutout temperature of 30 °C, the steering wheel electronics automatically switch on the steering wheel heater again. The cutout temperature of the steering wheel heater can be parameterized through the diagnosis tester.

 If no plausible interior temperature value is present, the outside temperature value is used instead.

 Switch-off during engine start

When the engine starts, the steering wheel electronics switch the steering wheel heater off. The timer control continues running, the steering wheel heater indicator lamp also remains on. The voltage drop during the engine starting procedure is not evaluated as undervoltage.

 Switching off in the event of undervoltage

At undervoltages of less than 10.0 V the steering wheel electronics switches off the steering wheel heater, and the steering wheel heater indicator lamp initially remains on. If the on-board electrical system voltage has been stabilized to normal voltage within the next 3 minutes, the steering wheel heater automatically starts up again. However, if the shutoff last longer than 3 minutes, then the steering wheel heater indicator lamp is also switched off. If the shutoff period persists and the function is requested again, the steering wheel heater indicator lamp lights up for 1.5 s and then goes out.

 Switching off in the event of overvoltage

At overvoltages greater than 15.5 V, the steering wheel electronics switches off the steering wheel heater. The timer control continues running, the steering wheel heater indicator lamp remains on. It can only be switched back on if the on-board electrical system voltage was stabilized at normal voltage. The overvoltage threshold of the steering wheel heater can be parameterized through the diagnosis tester.

 Switch-off after circuit 15R OFF

If the circuit has been changed from circuit 15R ON to circuit 15C ON, the steering wheel electronics switch the steering wheel heater off. The timer control keeps running for another 5 minutes. If circuit 15R is switched on again, the steering wheel electronics also switch the steering wheel heater back on.

 Shutoff at end of diagnosis:

After a diagnosis has been completed, the steering wheel electronics switch off the steering wheel heater.