Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Rear Window Wiper - Operation

When the driver moves the wipers and washers control switch to the rear window wiper position, the CJB detects a LIN bus message and will energize the rear window wiper relay which is integral with the RF Filter.

When energized, the rear wiper relay provides a power supply to the rear window wiper motor. The rear window wiper motor is operated intermittently by the CJB, with a delay between wipes which varies with vehicle speed from 11 seconds to 5 seconds. This can also be switched to 7 seconds for all speeds by Car Configuration File (CCF) by changing 'intermittent speed dependent option' to OFF.

The rear window wiper motor has an integral park switch. The park switch ensures the rear window wiper motor returns the rear wiper to the park position when the rear window wiper is switched off on the wipers and washers control switch.

The park switch is part of the rear window wiper motor gear wheel. When the rear window wiper moves from the park position, the park switch contacts are closed. When the rear window wiper nears the park position the park switch contacts are open and a ground path to the CJB is broken.

When the CJB receives a LIN bus signal from the wipers and washers control switch that rear window wiper operation is selected, the park switch is continually monitored by the CJB for stall purposes. When the wipers and washers control switch is moved to the off position and the CJB next senses the open circuit signal from the park switch, it will remove the power supplies rear window wiper relay, stopping the rear window wiper motor in the park position.

Reverse Rear Window Wiper Operation

If the windshield wipers are active and reverse gear is selected, the CJB will operate the rear window wiper motor.

On vehicles with automatic transmission, the reverse gear signal is created by the Transmission Control Module (TCM). The TCM broadcasts the reverse gear signal on the high speed Controller Area Network (CAN) powertrain systems bus to the Gateway Module (GWM). The GWM passes the signal to the CJB on the medium speed CAN body systems bus.

On vehicles with manual transmission, the reverse gear signal is generated by the reverse switch in the transmission. The reverse switch is connected directly to the CJB.

REAR WINDOW WASHER

When the driver moves the wipers and washers control switch to the rear window wash position, the CJB detects a LIN bus message and energizes the rear washer relay. Power is supplied through the relay contacts to the rear washer pump. The ground path for the pump is provided through the contacts of the de-energized front washer relay. Both front and rear washer relays are located in the CJB.

Rain/Light sensor - if fitted - Operation

The rain/light sensor contains a number of transmitter and receiver diodes which emit and receive infrared light. By comparing the received light signal against the known transmitted light signal, the rain/light sensor can determine the amount of water on the outer surface of the windshield.

NOTE:

A = Clean and dry windshield; B = Wet and dirty windshield

Rain/Light sensor - if fitted - Operation

  1. Windshield outer surface
  2. Optical element
  3. Transmitter diodes (100% light transmitted)
  4. Rain/light sensor assembly
  5. Receiver diodes (100% light received)
  6. Water droplets or water film
  7. Receiver diodes (less than 100% light received)
  8. Lost light

When the driver moves the wipers and washer control switch to the 'Auto' position, the CJB detects a LIN bus message and monitors LIN bus messages received from the rain/light sensor. The rain/light sensor provides LIN bus messages with values ranging from 0 to 7. A signal value of 0 is interpreted by the CJB as there being no water on the windshield.

A signal value from 1 to 6 is interpreted by the CJB as there being a small amount of water hitting the windshield. In this instance, the CJB initiates a slow wipe routine as detailed in the 'Windshield Wiper Slow Wipe' section above.

A signal value from 7 is interpreted by the CJB as there being a large amount of water hitting the windshield. In this instance, the CJB initiates a fast wipe routine as detailed in the 'Windshield Wiper Fast Wipe' section above.

Rain/Light sensor sensitivity can be adjusted by turning the rotary control on the wipers and washers control switch to the required position. Six different sensitivity settings are available, which are broadcast over the LIN bus to the CJB.

NOTE:

The CJB will only change from fast wipe to slow wipe if the rain/light sensor value is lower than 7.

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