Chevrolet Trax: Brake booster vacuum assist description and operation

Hydraulic Brakes Block Diagram

Fig. 193: Hydraulic Brakes Block Diagram

In order to assure that vacuum is available to the vacuum brake booster, the car can contain a vacuum pump either in addition to the normal intake manifold vacuum source or as stand-alone. The pump provides negative pressure when the engine cannot properly accommodate the requirement, e.g. cold start, heavy throttle, high altitude and turbo pressure.

Auxiliary Brake Booster Pump

The auxiliary brake booster pump is a secondary vacuum supply to the brake booster to maintain sufficient vacuum needed for brake assist.

Vacuum Brake Booster

Uses source vacuum to decrease effort required by driver when applying the brake.

When brake system input force is applied, air at atmospheric pressure is admitted to the rear of both vacuum diaphragms, providing a decrease in brake pedal effort required. When input force is removed, vacuum replaces atmospheric pressure within the booster.

Vacuum Source

Vacuum is supplied by engine vacuum or by the auxiliary brake booster pump.

Brake Booster Vacuum Sensor Without J41

The brake booster vacuum sensor is mounted on the vacuum brake booster and provides feedback to the electronic brake control module relative to the amount of vacuum available for the vacuum brake booster.

Brake Booster Vacuum Switch With J41

The low vacuum switch controls the 12 V to the relay coil in the brake vacuum assist pump. When more vacuum is needed the vacuum switch closes. The relay coil closes the relay contact and connects the electric motor to ground. The electric motor is fed with 12 V. When sufficient vacuum is reached the switch opens and the pump stops.

BRAKE WARNING SYSTEM DESCRIPTION AND OPERATION

Hydraulic Brakes Block Diagram

Fig. 194: Hydraulic Brakes Block Diagram

The purpose of the brake warning system is to warn the driver of the park brake being applied while the vehicle is being driven, a brake electronic brake distribution (EBD) failure and/or a low brake fluid level condition.

• When the ignition switch in the ON position and park brake is applied, the brake warning indicator lamp is illuminated. While the ignition switch is turned to the ON position, the battery voltage is provided to the brake warning indicator on the instrument panel cluster (IPC). When the park brake is applied, the park brake switch is grounded and the brake warning indicator is illuminated.
• EBCM monitors the EBD system. If EBCM detects EBD failure condition, EBCM sends a signal to IPC and IPC illuminates the brake warning indicator.
• Brake fluid level indicator switch is negative thermal coefficient (NTC) type. When the brake fluid level is too low, the brake warning indicator is illuminated by being grounded through the brake fluid level indicator switch.

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