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:

• Ignition state.
• Engine running (link from instrument pack).
• 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.

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.