Anti-Lock Brake System Control Module
| ITEM | DESCRIPTION |
|---|---|
| 1 | Rear right brake outlet port |
| 2 | Front left brake outlet port |
| 3 | Front right brake outlet port |
| 4 | Rear left brake outlet port |
| 5 | Primary circuit inlet port |
| 6 | Secondary circuit inlet port |
| 7 | Hydraulic Control Unit (HCU) |
| 8 | Electrical connector |
| 9 | Control module |
The Anti-lock Brake System (ABS) control module consists of an integrated control module and the four-channel Hydraulic Control Unit (HCU). The control module uses the HCU to modulate hydraulic pressure to the individual wheel brakes to control the brake and stability functions.
The ABS control module is secured to a mounting bracket located between the front suspension tower and the secondary bulkhead on the opposite side to the hand of drive. A multi-pin electrical connector provides the electrical interface between the control module and the vehicle wiring. Hydraulic pipes and hoses connect the HCU to the master cylinder and the brake calipers. The primary and secondary outlets of the master cylinder are connected to the primary and secondary circuits within the HCU. The primary circuit in the HCU has separate outlet ports to the front left and rear right brakes. The secondary circuit in the HCU has separate outlet ports to the front right and rear left brakes.
If an ABS modulator fault is detected, the 'ABS FAULT' message appears in the Instrument Cluster (IC) message center and the amber warning indicator comes on.
Hydraulic Control Unit
The Hydraulic Control Unit (HCU) is a four channel unit that modulates the supply of hydraulic pressure to the brakes, under the control of the Anti-lock Brake System (ABS) control module.
The master cylinder primary and secondary circuit outlets are connected to the HCU primary and secondary circuits.
Each of the HCU circuits contains the following components to control the supply of hydraulic pressure to the brakes:
- A normally open, solenoid-operated pilot valve, to enable active braking.
- A normally closed, solenoid-operated priming valve, to connect the brake fluid reservoir to the dual circuit hydraulic pump during active braking.
- A hydraulic pump, to generate hydraulic pressure for active braking and return brake fluid to the reservoir.
- Normally open, solenoid-operated inlet valves and normally closed, solenoid-operated outlet valves, to modulate the hydraulic pressure in the individual brakes.
- An accumulator and a relief valve, to allow the fast release of pressure from the brakes.
- Filters, to protect the internal components from contamination.
A pressure sensor in the primary circuit provides the ABS control module with hydraulic pressure signals. Contact pins on the HCU mate with contacts on the ABS control module to provide the electrical connections from the ABS control module to the dual circuit hydraulic pump motor and the pressure sensors. The solenoids that operate the valves are installed within the ABS control module.
The Hydraulic Control Unit (HCU) features three operating modes:
- Normal braking/Electronic Brake Force Distribution (EBD)
- ABS braking
- Active braking.
Normal Braking/Electronic Brake Force Distribution Mode
Initially, all of the solenoid-operated valves are de-energized. Operating the brake pedal produces a corresponding increase or decrease of pressure in the brakes, through the open pilot valves and inlet valves. If the ABS control module determines that EBD is necessary, it energizes the inlet valves for both the rear brakes, to isolate the brakes from any further increase in hydraulic pressure. Only the rear brakes are controlled by the EBD function.
Anti-lock Brake System Braking Mode
If the ABS control module determines that ABS braking is necessary, it energizes the inlet and outlet valves of the related brake and starts the hydraulic return pump. The inlet valve closes to isolate the brake from pressurized fluid. The outlet valve opens to release pressure from the brake into the accumulator and the return pump circuit. The reduced hydraulic pressure allows the wheel to accelerate. The ABS control module then operates the inlet and outlet valves to modulate the pressure in the brake to apply the maximum braking effort without locking the wheel. Control of the valves for each wheel takes place individually.
Active Braking Mode
The active braking mode is used to generate and control hydraulic pressure to the brakes for functions other than the normal/EBD and ABS braking modes.
For active braking, the ABS control module energizes the pilot valves and priming valves, starts the return pump and energizes all of the inlet valves. Brake fluid, drawn from the reservoir through the master cylinder and priming valve, is pressurized by the hydraulic pump and supplied to the inlet valves. The ABS control module then operates the inlet valves and outlet valves, as required, to modulate the pressure in the individual brakes. Some noise may be generated during active braking.
Service Information
ABS control module and the HCU form a single component and must not be separated. The ABS control module and HCU assembly is supplied in a prefilled state. After installation, the hydraulic brake system only requires a conventional bleeding of the brake system. There is no requirement to pressure bleed the system.