Body control unit (Heated screens): Description and operation

Heated screens

The heated screen time-outs and logical operations are controlled by the BCU.

Heated front screen The BCU provides an output to the heated front screen relay and a 'heated front screen active signal' for the heated front screen warning lamp. The BCU uses the status of the following inputs to determine the appropriate logical operations for this feature: l Ignition state. l Engine running (link from instrument pack). l Heated front screen selected (non-latched button pressed).

If the ignition switch is not in position II, or the engine running signal is OFF, the heated front screen will not be active.

The heated front screen operation period and voltage supply is controlled by the BCU. The BCU receives a voltage supply feed from the engine compartment fuse box and an ignition switched supply through a fuse in the passenger compartment fuse box. When the heated front screen switch is operated, it completes a path to earth, signalling a request for heated screen operation to the BCU. The BCU then supplies a feed to the heated front screen switch to light the switch indicator, and earths the supply from the coil of the heated screen relay to turn the heated front screen on. The BCU maintains a supply for a predetermined time (5 minutes), then opens the earth path after the time out period to turn the heated screen off. During the timeout period, if the heated front screen switch is pressed a second time, the circuit is also interrupted to turn off the supply to the heated front screen.

On vehicles fitted with air conditioning, the heated front screen is also operated by the ATC ECU when DEF (defrost) is selected. In this case the ATC ECU provides the trigger signal to the BCU to turn the heated front screen circuit on or, if it is already on, to re-start the time out period. AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.

In the event of a communications link failure occurring while the heated front screen relay is on, the relay and lamp will remain on until the ignition switch is turned off or the time-out period elapses or the heated front screen switch is pressed.

Heated rear window The heated rear window will only function when the engine is running, and is operated by a non-latching switch on the instrument pack cowl.

The BCU provides a 'heated rear window enable output' and a 'heated rear window active warning lamp signal' based on the logic status of the following inputs: l Ignition state. l Engine running (link from instrument pack). l Heated rear window selected (non-latched button pressed).

If the ignition switch is not in position II, or the engine running signal is OFF, the heated rear window will not be active.

The heated rear window operation period and voltage supply is controlled by the BCU. The BCU receives a voltage supply feed from the engine compartment fuse box and an ignition switched supply through a fuse in the passenger compartment fuse box. When the heated rear window switch is operated, it completes a path to earth, signalling a request for heated rear window operation to the BCU. The BCU then supplies a feed to the heated rear window switch to light the switch indicator, and earths the supply from the coil of the heated rear window relay via the IDM to turn the heated rear window elements on. The BCU maintains a supply for a predetermined time (15 minutes), then opens the earth path after the time-out period to turn the heated rear window operation off. If the heated rear window switch is pressed a second time, the circuit is also interrupted to turn off the supply to the heated front screen.

On vehicles fitted with air conditioning, the heated rear window is also operated by the ATC ECU when DEF (defrost) is selected. In this case the ATC ECU provides the trigger signal to the BCU to turn the heated rear window circuit on or, if it is already on, to re-start the time out period. AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.

In the event of a communications link failure occurring while the heated rear window enable is on, the relay and lamp will be de-activated.