LR3/Disco 3
The DAR pre-arming function operates when the transfer box is in high range to reduce the parking brake release time
during DAR and to provide a smooth take-off. DAR pre-arming is invoked when:
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The ignition switch is in position II.
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The transmission is in gear 1, 2 or R.
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The vehicle is stationary.
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No failsafe tighten actuation has occurred.
Automatic Load Adjustment
While the ignition is on, the parking brake module constantly monitors the input from the force sensor. If the tension of the
brake cables goes outside the limits for a given operating mode, the parking brake module automatically restores the
tension within limits.
Failsafe Tighten. If, during pre-arming, the vehicle moves, then the maximum cable force is reinstated for the remainder
of that ignition cycle.
Automatic Apply. While the parking brake is applied, if the tension of the brake cables decreases by a prescribed
amount from the initial setting, the parking brake module automatically restores the tension to the initial setting.
Automatic Release. While the parking brake is released, if the tension of the brake cables increase to a prescribed
amount, the parking brake module automatically reduces the tension to zero.
Parking Brake Switch Monitoring
The parking brake module monitors for the following types of fault in the parking brake switch system. If a fault is
detected, the parking brake module stores a related fault code:
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Short circuits between a pull-down transistor in the parking brake module and battery voltage.
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Broken wires and microswitches.
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Plausibility.
The parking brake switch has a degree of in-built redundancy. If a single microswitch fault is detected the parking brake
module can still determine the operating state of the parking brake switch. Short circuits or multiple failures cause the
parking brake module to disable the parking brake switch for the remainder of the ignition cycle. The parking brake
module also disables the parking brake switch if a plausibility fault occurs. However, since plausibility faults are usually
caused by incomplete operation of the parking brake switch, the parking brake switch is re-enabled if the parking brake
module subsequently establishes a plausible operating state.
If a single microswitch fault is detected, the parking brake module signals the instrument cluster to illuminate the amber
parking brake warning indicator. On vehicles with the high line instrument cluster, the parking brake module also signals
the instrument cluster to display a message advising there is a parking brake fault. During an apply actuation, the parking
brake module also signals the instrument cluster to flash the red parking brake warning indicator.
For all other fault types, the parking brake module signals the instrument cluster to illuminate the amber parking brake
warning indicator, and, on vehicles with the high line instrument cluster, to display a message advising the parking brake
has a fault and is not functioning. If it makes an apply actuation, the parking brake module signals the instrument cluster
to flash the red parking brake warning indicator for the remainder of the ignition cycle.
On the next ignition cycle, the warning indicators and the messages are only activated if the fault is still present, although
the fault code is retained by the parking brake module until cleared by T4.
PARKING BRAKE CONTROL DIAGRAM
NOTE:
A = Hardwired connection; D = High speed CAN bus; N = Medium speed CAN bus
