The ABS module is attached to the HCU and forms an integral part with it. The 47-pin electrical connector provides the electrical connection between the ABS module and the vehicle's electrical wiring. It is possible to read information from the ABS module using Land Rover approved diagnostic equipment.
Hydraulic control box
The HCU is a 4-channel unit that modulates the hydraulic pressure supply to the brakes under the control of the ABS module.
The outputs of the primary and secondary circuits of the master cylinder are connected to the primary and secondary circuits of the HCU. For more information, see chapter: Hydraulic brakes (206-06 Hydraulic brakes, Description and principle of operation). Each of the HCU circuits contains the following elements that allow you to control the supply of hydraulic pressure to the brakes:
- Normally open solenoid controlled pilot valve to provide active braking.
- Normally closed solenoid operated filling valve to connect the brake fluid reservoir to the dual circuit hydraulic pump when braking is active.
- Hydraulic pump to generate hydraulic pressure for active braking and return brake fluid to the reservoir.
- Solenoid operated normally open intake valves and solenoid operated normally closed exhaust valves to modulate hydraulic pressure in individual brakes.
- Accumulator and relief valve to allow quick depressurization of the brakes.
- Filters to protect internal elements from contamination.
The primary circuit also includes a pressure sensor that provides the ABS module with a hydraulic pressure signal.
The pins on the HCU mate with pins on the ABS module to provide electrical connections between the ABS module and the dual circuit hydraulic pump motor and pressure sensor. The solenoid valves that actuate the valves are installed in the ABS module.
HCU diagram
Pos. | spare part no | Name |
1 | - | Vacuum brake booster |
2 | - | Primary hydraulic circuit |
3 | - | Secondary hydraulic circuit |
4 | - | Pulsation dampener |
5 | - | Pulsation dampener |
6 | - | HCU |
7 | - | Damping chamber |
8 | - | Double circuit hydraulic pump |
9 | - | DC electric motor |
10 | - | Solenoid control valve (2 pcs.) |
11 | - | Solenoid filling valve (2 pcs.) |
12 | - | check valve |
13 | - | Low pressure accumulator (2 pcs.) |
14 | - | Solenoid inlet valve (right rear brake) |
15 | - | Solenoid inlet valve (left front brake) |
16 | - | Solenoid outlet valve (left front brake) |
17 | - | Solenoid outlet valve (right rear brake) |
18 | - | Pressure meter (5 pieces.) |
19 | - | Left front brake (secondary circuit) |
20 | - | Right rear brake (secondary circuit) |
21 | - | Left rear brake (primary circuit) |
22 | - | Right front brake (primary circuit) |
23 | - | Solenoid outlet valve (right front brake) |
24 | - | Solenoid outlet valve (left rear brake) |
25 | - | Solenoid inlet valve (left rear brake) |
26 | - | Solenoid inlet valve (right front brake) |
HCU has three working modes:
- Normal braking/EBD
- Braking with ABS
- Active braking
Normal braking / EBD mode
Initially, all solenoid valves are turned off. The operation of the brake pedal causes a corresponding increase or decrease in pressure in the brakes, through the open control valves and intake valves. If the ABS module determines that EBD work is needed, it will activate the intake valves for both rear brakes to prevent any further increase in brake hydraulic pressure.
NOTE: The EBD function only controls the rear brakes.
Braking mode with ABS
If the ABS module determines that ABS braking is required, it activates the appropriate brake inlet and outlet valves and turns on the hydraulic return pump. The intake valve closes to isolate the pressurized fluid from the brake; the bleed valve opens to release pressure from the brake to the accumulator and return pump circuit. The reduced hydraulic pressure allows the wheel to accelerate. The ABS module then activates the intake and exhaust valves to modulate brake pressure to apply maximum braking force without locking up the wheel. The valves for each wheel are individually controlled.
Active braking mode
The active braking mode is used to generate and control the hydraulic pressure supplied to the brakes for functions other than normal braking and braking with ABS, such as RSC, DSC, EBA, ETC, HDC.
When braking is active, the ABS module activates the control valves and filling valves, starts the return pump, and activates all intake valves. Brake fluid, which is drawn from the reservoir through the master cylinder and filling valve, is pumped by the return pump and fed to the intake valves. The ABS module then activates the intake and exhaust valves as needed to modulate individual brake pressure. There may be some noise during active braking.
Service Information
ABS module includes HCU and electronic control unit (ECU) and should not be shared. The ABS module with HCU is shipped as a single unit pre-charged.
NOTE: The ABS module, HCU, and sensor unit are fragile items and should be discarded if dropped or damaged.
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