Window Glass: Description and Operation

GF67.29-D-0003H Heated Rear Window, Function

- with CODE (H22) Heated rear window

- with CODE (W78) Window in tailgate or hinged rear door with wipe/washer system

Activation

Function requirements:
- Circuit 61 ON
- Stable idle mode
- No overvoltage or undervoltage present

Overvoltage is present when voltage > 15 V.
Undervoltage is present when voltage < 10.5 V.

The heated rear window system is activated by actuating the rear window heater button (N72/1s3) which is integrated into the UCP control unit (N72/1). The UCP control unit stores the message "UCP_A1 HHS_ON (heated rear window ON)" on the controller area network, class B (interior compartment) (CAN B).

The rear SAM control unit (N10) receives this message. It then first checks the heating wires of the left heated rear window (R1/1) and the right heated rear window (R1/2). Then the rear SAM control unit actuates the left heated rear window and right heated rear window via the heated rear window relay 1 (K13/5) or heated rear window, relay 2 (K13/6).

The rear SAM control unit transmits the message "SAM_A4 HHS_ON (heated rear window ON)" via CAN B to the UCP control unit and monitors this message.If there is a discontinuity in the heating wires in the left heated rear window or the right heated rear window, the rear SAM control unit transmits the message "SAM_A4 HHS_UB (heated rear window discontinuity)" to the UCP control unit via CAN B.

Activation of the RWD system is indicated permanently by the LED in the rear window heater button in the UCP control unit. If the UCP control unit does not receive feedback within t = 700 ms by the SAM control unit, the LED in the rear window heater button flashes for t = 5 s. If the feedback appears within t = 5 s, the LED in the rear window heater button comes on permanently, otherwise the LED in the rear window heater button goes out.

If the rear window heater button is pressed for longer than t = 25 s, the message "UCP_A1 HHS_ON (heated rear window ON)" is canceled, the RWD system is not activated and an error is stored.This is indicated by an LED flashing the rear window heater button for t = 5 s. As soon as the rear window heater button is released for t = 1 s, the RWD system can be reactivated by actuating the heated rear window button.

If the UCP control unit recognizes that the voltage is too low before the RWD is activated, the message "UCP_A1 HHS_ON (heated rear window ON)" is not transmitted and the LED in the rear window heater button flashes for t = 5 s.

Deactivation

The RWD system is deactivated if one of the prerequisites is present:
- The rear window heater button is actuated again.
- The maximum switch-on duration of t = 15 min is reached.
- Status "Circuit 61 OFF" is present.

The UCP control unit transmits the message "SAM_A4 HHS_AUS (heated rear window OFF)" via CAN B to the SAM control unit.Deactivation is indicated when the LED in the rear window heater button goes out.

Temporary deactivation

The RWD system is deactivated temporarily if one of the prerequisites is present:
- Idle not stable.
- Voltage too low or too high

If idle is not stable, the message "LL_STBL_B = 0 (idle not stable) from the CDI control unit (N3/20), with engine OM642, from the CDI control unit (N3/21), with engine OM642, or from the ME-SFI control unit (N3/23), with engine M272 is stored on the CAN B bus. The UCP control unit reads in this message and deletes the message on the "UCP_A1 HHS_ON (heated rear window ON)". If the UCP control unit reads the message "LL_STBL_B = 1 (idle stable)", it transmits the message "UCP_A1 HHS_ON (heated rear window ON)" to the CAN control unit via CAN B. Temporary deactivation when idle is not stable is not indicated; the LED rear window heater button maintains its status.

If voltage is too low or too high, the UCP control unit deletes the message UCP_A1 HHS_ON (heated rear window ON)". Temporary deactivation when voltage is too low or too high is indicated by an LED flashing in the rear window heater button for t = 30 s.

If the threshold value is exceeded when the voltage is too low, the UCP control unit transmits the message "UCP_A1 HHS_ON (heated rear window ON)" to the SAM control unit via CAN B. Otherwise the message "UCP_A1 HHS_ON (heated rear window ON)" remains deleted; the LED in the rear window heater button flashes for t = 5 s and then goes out.