Rear Seat Heating, Checking

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Components Which Participate In the Activation of the Rear Seat Heating

Rear seat heating activation depends on the version and equipment of the vehicle.

NOTE:

In vehicles without a Rear A/C Display Control Head -E265-, the rear seat heating is adjusted via the Left Rear Heated Seat Regulating Switch -E128- or Left Rear Heated Seat Switch -E77- and the Right Rear Heated Seat Regulating Switch -E129- or Right Rear Heated Seat Switch -E78-. The Left Rear Bench Seat Heating Element -Z10-, Left Rear Backrest Heating Element -Z11-, Right Rear Bench Seat Heating Element -Z12- and Right Rear Backrest Heating Element -Z13- are activated by the Rear Seat Heating Control Module -J786-. This control module is currently not On Board Diagnostics (OBD)-capable. However, activation only occurs when the Vehicle Electrical System Control Module -J519- provides the corresponding release. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" Function and to the appropriate WIRING DIAGRAM.

For vehicles with Rear A/C Display Control Head -E265-, seat heating and seat ventilation for the rear seats are set via the Rear A/C Display Control Head -E265-. The Rear A/C Display Control Head -E265- then activates the rear seat heating as a function of the vehicle equipment and version.

In vehicles without a Driver Side Rear Seat Adjustment Control Module -J876- and a Passenger Side Rear Seat Adjustment Control Module -J877-, the Rear A/C Display Control Head -E265- activates the rear seat heating. The rear seat heating is activated by the Rear A/C Display Control Head -E265- if the Vehicle Electrical System Control Module -J519- does not receive a condition prohibiting seat heating activation. The -J519- first sends the request via the data bus to the Data Bus On Board Diagnostic Interface -J533- and then via the control head, the Climatronic Control Module -J255- to the -E265-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function and to the appropriate WIRING DIAGRAM (for the particular vehicle system).
In vehicles with a Driver Side Rear Seat Adjustment Control Module -J876- and a Passenger Side Rear Seat Adjustment Control Module -J877-, the Rear A/C Display Control Head -E265- activates the rear seat heating. In this case, activation is performed by the Driver Side Rear Seat Adjustment Control Module -J876- and the Passenger Side Rear Seat Adjustment Control Module -J877-. The request to switch on the seat heating is sent via the Rear A/C Display Control Head -E265- to the Climatronic Control Module -J255- control head. It first sends the request via the data bus to the Data Bus On Board Diagnostic Interface -J533-. The request is then relayed to the Driver Side Rear Seat Adjustment Control Module -J876- and a Passenger Side Rear Seat Adjustment Control Module -J877-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" Function and to the appropriate WIRING DIAGRAM (for the particular vehicle system).
A start-stop system is available for certain engines of this vehicle. For vehicles with a Start/Stop System, the seat heating is switched off while the stop function is active (to protect the Battery -A-). The setting for seat heating activation remains stored in the Rear A/C Display Control Head -E265-. After the engine was started again via the start function, the seat heating is switched on again. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

NOTE:

Seat heating activation can differ, depending on the vehicle version. Refer to to the appropriate WIRING DIAGRAM.

Depending on the version and equipment of the vehicle, the various information regarding seat heating activation (the setting transmitted by the Rear A/C Display Control Head -E265-, the target and actual temperature of the seat, etc.) is displayed in different measured value blocks in various control modules. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

In the event of a condition preventing heating of the rear seat (for example short circuit in the connection to the seat heating element, open circuit in the voltage supply to the particular control module, etc.), this is stored as a malfunction in the Rear A/C Display Control Head -E265-, in the Vehicle Electrical System Control Module -J519-, the Climatronic Control Module -J255- control head, in the Data Bus On Board Diagnostic Interface -J533-, in the Driver Side Rear Seat Adjustment Control Module -J876- or in the Passenger Side Rear Seat Adjustment Control Module -J877- (depending on the vehicle version and the vehicle equipment). In this vehicle, information stating that the event memory in the relevant control module needs to be read out may not be sent via the data bus to the Rear A/C Display Control Head -E265-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. In the event of a complaint regarding seat heating, first check the event memory of the control modules activating the seat heating.

The function test of seat heating activation is described in the Guided Fault Finding for the relevant control module (Rear A/C Display Control Head -E265-, Driver Side Rear Seat Adjustment Control Module -J876- or Passenger Side Rear Seat Adjustment Control Module -J877-, depending on the vehicle version and equipment). Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

If, for example, the voltage at terminal "30" measured at the Vehicle Electrical System Control Module -J519- falls below a value stored in the -J519-, the seat heating output is reduced or switched off completely in order to reduce the load of the Generator -C-. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

The "read measured value block" function in the Guided Fault Finding of the Rear A/C Display Control Head -E265- displays which seat heating setting has been selected. The seat heating, the actual and target seat temperature, the actual current supplied to the seat heating, etc. are displayed as a function of the version and equipment of the vehicle in the "read measured values" function of the Guided Fault Finding of the relevant control module. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

Depending on the vehicle version, the rear seat heating can switch off after a certain period of time when it is detected that the seat is not occupied (deactivation via the passenger occupant detection system is not planned for the start of production, introduction not yet finalized). Refer to the Operating instructions.