How the parking brake works (Discovery 3)

The parking brake can be applied at any time, provided that the battery provides sufficient voltage. To release the parking brake, certain prerequisites must be met. The parking brake has manual and automatic modes of operation for different conditions, as discussed in the following table:

Operating modes

Mode	Prerequisites	Driver's action
Static inclusion	The vehicle speed is less than 2.5 km/h.	Pull the parking brake switch up.
Static Shutdown	1, Vehicle speed is less than 2.5 km/h. 2, Engine is running. OR Ignition switch is in position II and brake pedal or clutch pedal is pressed. (for models with manual transmission). OR The ignition key is in position II and the accelerator pedal or clutch pedal is pressed (for models with automatic transmission).	Press the parking brake switch down.
Turn on when key is removed (only for models with manual transmission)	1, Vehicle speed less than 10 km/h. 2, Ignition key in position 0. 3, Key in ignition switch.	Remove the key from the ignition.
Disable power on when key is removed	1, Vehicle speed less than 2.5 km/h. 2, Ignition key in position 0. 3, Key in ignition switch.	Remove the key from the ignition switch while holding down the parking brake switch.
Dynamic inclusion	The vehicle speed is more than 2.5 km/h.	Pull the parking brake switch up as required.
Dynamic shutdown	The vehicle speed is more than 2.5 km/h.	Turn it off (move to neutral position) or press down the parking brake switch.
DAR (automatic shutdown when starting to move) (only for models with automatic transmission)	1, Ignition key in position II. 2, Gear selector in position 1, 2 or R. (with the highest level selected) or 1, 2, 3 or R (with the lowest step selected).3, The accelerator pedal is pressed more than 5%.	None. The parking brake is released automatically when you start moving.

Working voltage

Putting into action (turn on or off) the parking brake can only be applied when the supply voltage of the parking brake control unit is in the range of 9-18 V. At any voltage in this range, the parking brake control unit can provide maximum tension to the brake cables, fully engaging the parking brake. However, in the range of 9-10.5 V, the actuation time may exceed 1 second.

When applying the parking brake:

• If the supply voltage of the parking brake control module drops below 8.3 V, the parking brake control module continues to operate but stores the corresponding fault code. If the ignition is on, the parking brake control module also transmits signals to the instrument cluster to turn on the yellow parking brake indicator and flash the red parking brake indicator. For vehicles with a high-level instrument cluster, a parking brake malfunction message is displayed in the message center display. The warnings are cleared when the supply voltage exceeds 8.3 V.
• If the supply voltage drops below 7.5 V, the parking brake control unit stops the operation. The operation is resumed automatically when the supply voltage exceeds 7.5 V and the command from the parking brake switch is still received.
• If the supply voltage drops below 6.5 V, the parking brake function is disabled for the remainder of the ignition cycle.
• If the supply voltage exceeds 18.0 V, the parking brake control unit immediately disables the parking brake function and stores a corresponding fault code. If the ignition is on, the parking brake control unit also transmits signals to the instrument cluster to illuminate the yellow parking brake indicator and flash the red parking brake indicator. For vehicles with a high-level instrument cluster, a message is displayed in the message center display stating that the parking brake is faulty and does not work. The parking brake function is disabled until the supply voltage is back within the range of 9-18 V. When the supply voltage returns to the range of 9-18 V, the warnings stop and the operation is automatically resumed if the parking brake control unit is operating in dynamic mode with a valid request from the parking brake switch.

NOTE: When the voltage is below 8 V, the instrument cluster turns off, so when the voltage is below 8 V, the indicators do not work and no warnings are given. Data transmission on the CAN bus stops when the battery voltage is below 7.0 and resumes when the voltage is above 7.5 V.

Standby mode

To reduce the battery drain at rest, the parking brake control unit has a sleep mode. The parking brake control unit enters the sleep mode when the ignition is off and no signals are received from the wheel speed sensors when one of the following conditions is met:

• 20 minutes have passed since the parking brake was last applied.
• If the parking brake has not been applied, 20 minutes have passed since the ignition was turned off.

The parking brake control unit exits standby mode when one of the following conditions is met:

• The parking brake switch has requested to be turned on or off.
• The ignition is on.
• Turning on occurred when key was removed.

The parking brake control unit wakes up from standby mode within 500 ms. High-speed CAN bus (controller network) turns on in no more than 200 ms.

If the parking brake control unit is awakened from standby mode by a request to release from the parking brake switch, the parking brake control unit ignores this request and turns on the red brake indicator. The parking brake control unit turns off the red brake indicator and returns to standby mode immediately after the switch is moved to the neutral position.

If the parking brake control unit is awakened from standby mode by an on request from the parking brake switch and the parking brake is already applied, the parking brake control unit ignores the request and turns on the red brake indicator. The parking brake control unit turns off the red brake indicator and returns to standby mode immediately after the switch is moved to the neutral position. If the parking brake is not turned on when the on request is received, the parking brake control unit turns on the red brake indicator and the parking brake. The parking brake control unit turns off the red brake indicator and returns to standby mode 3 minutes after it is turned on, or immediately after the switch is moved to the neutral position, depending on which event occurred last.

Dynamic inclusion

In dynamic engagement mode, the system operates as follows. When the speed exceeds 10 km/h with the parking brake switch in the on position, the parking brake control unit sends a request to the ABS module to engage the disc brakes on all four wheels. When the vehicle comes to a complete stop, the parking brake control unit statically engages the parking brake. When the static load is reached, the hydraulic pressure is released. If the parking brake switch is released to the neutral position or pressed down to the off position during dynamic engagement, braking is stopped.

ABS module (anti-lock braking system) controls deceleration based on wheel speed sensor signals and regulates hydraulic pressure on the brake discs to achieve the required deceleration. When operating in dynamic activation mode, all functions of the anti-lock and anti-slip systems are active.

The parking brake control unit has two fault neutralization functions for the dynamic engagement mode.

• Fault neutralization function 1 is activated when the speed is between 2.5 km/h and V, the parking brake switch is in the on position, and the ABS module (anti-lock braking system) cannot generate the required hydraulic pressure. When the Fault Neutralization Function 1 is activated, the parking brake control unit brakes the vehicle using the parking brake only. The parking brake control unit controls deceleration based on wheel speed information from the ABS module. (anti-lock braking system) and adjusts the brake cable tension to achieve the desired deceleration. Also during deceleration, the parking brake control unit uses wheel speed signals from the ABS module (anti-lock braking system) to control the anti-lock function of the rear wheels. When the vehicle speed drops to 2.5 km/h, the parking brake control unit switches to static engagement mode.
• Fault neutralization function 2 is activated when the information transfer between the parking brake control unit and the ABS module is interrupted. (anti-lock braking system), or CAN bus malfunctions (controller network). When the fault recovery function 2 is activated, the parking brake control unit brakes the vehicle using only the parking brake. The parking brake control unit tensions the brake cables under the driver's control, and the anti-lock function is not available.

When the brake is applied dynamically, including the fault recovery functions 1 and 2, the parking brake control unit also transmits via the high-speed CAN bus (controller network) signals to the following devices:

• ABS module (anti-lock braking system) to turn on the brake lights.
• Instrument cluster for switching on intermittent warning signal (active signal 0.5 s, pause 1.0 s).
• Instrument cluster for turning on the red parking brake indicator. The indicator lights up continuously, except when the fault 2 function is activated, when it flashes.

Preliminary preparation of DAR

DAR pre-conditioning is performed when the transfer case is in the highest gear and serves to reduce the parking brake release time during smooth starting using the DAR function. DAR pre-conditioning is performed in the following situation:

• The ignition switch is in position II.
• The gearbox operates in 1, 2 or R mode.
• The car is stationary.
• The cables are not tensioned in emergency mode.

Automatic load regulation

When the ignition is on, the parking brake control unit constantly monitors the signal from the force sensor. If the brake cable tension goes beyond the limits set for the current mode, the parking brake control unit automatically returns the tension to the permissible range.

Tension in emergency mode. If the vehicle is moving during preconditioning, the cables are set to maximum tension until the end of the current ignition cycle.

Automatic switching on. If the brake cable tension decreases by a specified amount relative to the initial setting while the parking brake is applied, the parking brake control unit automatically restores the tension to the initial setting.

Automatic shutdown. If the brake cable tension increases by a specified amount when the parking brake is released, the parking brake control unit automatically reduces the tension to zero.

Parking brake switch control

The parking brake control module monitors the parking brake switch system to detect the following faults. If a fault is detected, the parking brake control module stores the corresponding fault code:

• Short circuits between the matching transistor in the parking brake control unit and the battery voltage circuit.
• Wire breaks and microswitch malfunctions.
• Reliability.

The parking brake switch has internal redundancy. If a fault is detected in one microswitch, the parking brake control unit can still determine the state of the parking brake switch. Short circuits or multiple faults cause the parking brake control unit to disable the parking brake switch for the remainder of the current ignition cycle. In addition, the parking brake control unit disables the parking brake switch if a plausibility error is detected. However, since plausibility errors are usually caused by incomplete operation of the parking brake switch, the switch is restored to operation if the parking brake control unit subsequently determines that the switch is in a valid operating state.

When a single microswitch fault is detected, the parking brake control unit sends a signal to the instrument cluster to turn on the yellow parking brake indicator. On vehicles with a high-level instrument cluster, the parking brake control unit also sends a command to the instrument cluster to display a parking brake fault message. During activation, the parking brake control unit also sends a request to the instrument cluster to flash the red parking brake indicator.



For all other types of faults, the parking brake control unit transmits a signal to the instrument cluster to turn on the yellow parking brake indicator and, for vehicles with a high-level instrument cluster, a command to display a message stating that the parking brake is faulty and does not work. If it is turned on, the parking brake control unit transmits a signal to the instrument cluster to flash the red parking brake indicator until the end of the current ignition cycle.

At the next ignition cycle the indicators are illuminated and messages are given only if the fault is still present, although a fault code is stored in the parking brake control module until it is cleared using T4.