Chevrolet Equinox Service Manual: Brake Assist System Description and Operation

System Component Description

The brake assist system consists of the following:

Receives, multiplies and transfers brake system input forcefrom driver.

Transfers multiplied input force received from brake pedal tobrake booster.

Uses source vacuum to decrease effort required by driver whenapplying brake system input force.

At rest, source vacuum is applied to both sides of the vacuumdiaphragm for single boosters, or to both sides of each of thediaphragms for tandem boosters. Return springs maintain the boosterin a rest position.

When brake system input force is applied, vacuum to the rearof the diaphragm(s) is cut off, and air at atmospheric pressure isadmitted in its place. This provides a decrease in brake pedaleffort required. When input force is removed, vacuum again replacesatmospheric pressure within the booster.

Supplies force used by vacuum brake booster to decrease brakepedal effort.

The primary source for vacuum is typically the vehicle'sinternal combustion engine. Some vehicles may use a vacuum pump toensure and adequate supply of vacuum under various operatingconditions, such as during cold start-up, heavy throttle, and highaltitude.

Vehicles equipped with a vacuum pump will typically beequipped with a relay used to provide voltage to the vacuum pumpmotor, when commanded by the powertrain controller.

Provides a feedback voltage signal relative to the amount ofvacuum available for the vacuum power brake booster.

This typically consists of a vacuum sensor mounted eitherinto the power vacuum brake booster, integrated with the vacuumcheck valve, or in-line within the vacuum hose. The sensor feedbackis typically monitored by the powertrain control module(s).

If equipped with a system to monitor available levels ofvacuum for the brake assist system, the powertrain controlmodule(s) typically perform the primary monitoring function.

The powertrain controller will typically monitor the feedbacksignal of a vacuum sensor, as it relates to available vacuum at thevacuum power brake booster. The powertrain controller uses theinformation to make sure available vacuum remains abovepredetermined levels. If additional vacuum is required, thepowertrain controller may reactivate engine cylinders, if equipped,or command a vacuum pump ON, if equipped, and/or may alter theoperation of various other engine controls and devices, asnecessary.

Enables delivery and retention of source vacuum for vacuumbrake booster.

This typically consists of a vacuum check valve and a vacuumhose or pipe. If a vacuum pump is used, additional check valves maybe used.

Brake system input force from the driver is multiplied by thebrake pedal and transferred by the pedal pushrod to the hydraulicbrake master cylinder. Effort required to apply the brake system isreduced by the operation of the vacuum brake booster.

When brake system force is applied, vacuum to the rear of thediaphragm(s) is cut off, and air at atmospheric pressure isadmitted in its place. The vacuum acts to pull the diaphragm(s)forward, while the atmospheric pressure acts to push from behind.As a result, the amount of effort required by the driver isreduced. When input force is removed, vacuum again replacesatmospheric pressure within the vacuum power brake booster to helpreturn the booster to rest. Return springs maintain the system in arest position.

If the vehicle is equipped with a vacuum monitoring system,the powertrain control module(s) typically will alter powertrainfunctions and/or command the vacuum pump ON, if equipped, toprovide for the vacuum needs of the brake assist system, asoperating conditions warrant.