Chevrolet Silverado / GMC Sierra. Manual — part 2395

The IPC detects a low brake fluid condition. The IPC receives a low brake fluid signal from
the low brake fluid switch in the master cylinder reservoir requesting illumination.

The electronic brake control module (EBCM) detects an ABS malfunction which disables
dynamic rear proportioning (DRP). The IPC receives a GMLAN message from the EBCM
requesting illumination.

The IPC performs the bulb check at the start of each ignition cycle. The Red Brake Warning
indicator illuminates for approximately 3 seconds before turning OFF.

The IPC detects a loss of GMLAN communications with the EBCM.

HYDRAULIC BRAKE SYSTEM DESCRIPTION AND OPERATION

System Component Description

The hydraulic brake system consists of the following:

Hydraulic Brake Master Cylinder Fluid Reservoir

Contains supply of brake fluid for the hydraulic brake system.

Hydraulic Brake Master Cylinder

Converts mechanical input force into hydraulic output pressure.
Hydraulic output pressure is distributed from the master cylinder through 2 hydraulic
circuits, supplying front-rear opposed wheel apply circuits.

Hydraulic Brake Pressure Balance Control System

Regulates brake fluid pressure delivered to hydraulic brake wheel circuits, in order to
control the distribution of braking force.
Pressure balance control is achieved through dynamic rear proportioning (DRP), which is a
function of the ABS modulator. Refer to ABS Description and Operation (With JL4) or
ABS Description and Operation (Without JL4) for specific information on the
operation of DRP.

Hydraulic Brake Pipes and Flexible Brake Hoses

Carries brake fluid to and from hydraulic brake system components.

Hydraulic Brake Wheel Apply Components

Converts hydraulic input pressure into mechanical output force.

2008 Chevrolet Silverado 1500

2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

System Operation

Mechanical force is converted into hydraulic pressure by the master cylinder, regulated to meet
braking system demands by the pressure balance control system, and delivered to the hydraulic
brake wheel circuits by the pipes and flexible hoses. The wheel apply components then convert
the hydraulic pressure back into mechanical force which presses linings against rotating brake
system components.

BRAKE ASSIST SYSTEM DESCRIPTION AND OPERATION (HYDRAULIC ASSIST)

Fig. 50: View of Brake Assist System
Courtesy of GENERAL MOTORS CORP.

Callout

Component Name

1

Master Cylinder

2

Power Brake Booster Outlet Hose

3

Power Brake Booster Inlet Pipe/Hose

4

Hydraulic Brake Booster

5

Power Steering Gear Inlet Pipe/Hose

2008 Chevrolet Silverado 1500

2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

System Component Description

The brake assist system consists of the following:

Brake Pedal

Receives, multiplies and transfers brake system input force from driver.

Brake Pedal Pushrod

Transfers multiplied input force received from brake pedal to brake booster.

Hydraulic Brake Booster

Uses power steering fluid pressure to decrease effort required by driver when applying
brake system input force.

Power Steering System

Supplies pressurized power steering fluid used by hydraulic brake booster to decrease brake
pedal effort.

System Operation

The hydraulic brake boost system uses fluid from the power steering pump (8) through the
hydraulic boost inlet hose (3) and to the brake booster assembly (4). In addition to supplying the
brake system with fluid for increased apply, the power steering pump is also connected to the
power steering gear (6) and cooler (7).

The steering pump (8) is a continuous flow device supplying approximately 3 GPM at 1000
RPM, at the pump shaft. The fluid flows through the booster spool valve, then the return hose (5),
and then to the steering gear (6). Pressure is produced by applying the brake pedal, resulting in
the spool valve being actuated, internal to the hydraulic brake booster. The spool valve produces
a marginal restriction that causes pressure in the booster (4) to rise and forces the power piston
and therefore the output rod forward to generate force and motion at the master cylinder (1). The
brake corners are actuated by the fluid impulse generated by the master cylinder (1). Internal
blow by, or pressure relief, is directed to the low pressure return hose (2) back to the power

6

Steering Gear

7

Power Steering Cooler

8

Power Steering Pump

2008 Chevrolet Silverado 1500

2008 BRAKES Hydraulic Brakes - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado