ABS Description and Operation. Chevrolet Prizm 2001

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2001 🢒 Prizm 🢒 Brakes 🢒 Antilock Brake System 🢒 ABS Description and Operation

System Description

This vehicle is equipped with the Lucas/Sumitomo hybrid non-integral Antilock Brake System (ABS). The system employs a single valve per channel, 4-channel system to reduce the tendency of any wheel to lock-up. This improves driver control of the vehicle during braking. The purpose of the ABS is to minimize wheel lockup during heavy braking on most road surfaces. The ABS performs this function by monitoring the speed of each wheel and then controlling the brake fluid pressure to each wheel independently during a braking maneuver. This allows the driver to retain directional stability and allows the driver better steering capability.

The purpose of the ABS is to minimize wheel slipping during braking, thus improving vehicle stability and steerability. The ABS accomplishes this objective by controlling the hydraulic pressure applied at each front wheel brake and both rear wheel brakes as a pair.

The ABS operation is available from approximately 6.3 km/h (4 mph) to the maximum vehicle speed. During braking the ABS is available from the maximum vehicle speed to 5 km/h (3 mph).

Electronic Brake Control Module (EBCM)/Brake Pressure Modulator Valve (BPMV)


(1)	Master Cylinder
(2)	BPMV Wiring Harness Connector
(3)	EBCM/BPMV Assembly
(4)	EBCM/BPMV Mounting Bracket
(5)	Brake Vacuum Booster

The BPMV assembly is a compact integrated unit that contains the following components:

•

An EBCM

•	Four solenoid valves (one for each wheel brake hydraulic channel)

•	Four flow control valves in-series with each wheel brake hydraulic channel (one for each solenoid valve)

•	Buffer chambers

•	A pump motor

•	Check valves

The BPMV assembly is located on the left rear corner of the engine compartment just below the master cylinder. The BPMV assembly is mounted on a bracket.

The controlling element of the ABS is a microprocessor based EBCM. The inputs to the system include the following components:

•	The four wheel speed sensors

•	The stoplamp switch

•	The ignition switch

•	The battery voltage

•	The OBD2 Data Link Connector (DLC)

The outputs include the following components:

•	The four solenoid valves

•	The pump motor

•	The ABS indicator

•

The DLC

The EBCM monitors the speed of each wheel. If any wheel begins to slip during braking, the EBCM actuates the solenoid valves and the pump motor to modulate hydraulic pressure to the wheel brake(s) approaching slip. Once the wheel regains traction the hydraulic pressure is increased until the wheel again begins to slip. This cycle repeats until any of the following happens:

•	The vehicle comes to a stop.

•	The brake pedal is released.

•	No wheels approach slippage.

Additionally the EBCM monitors each input and each output for proper operation. The EBCM sets a Diagnostic Trouble Code (DTC) when it detects a system malfunction. The DTC will not clear when the battery is disconnected because the EBCM stores DTCs in nonvolatile memory. The EBCM is an integral part of the BPMV assembly and is not serviceable separately.

Front Wheel Speed Sensors and Rings


(1)	Front Wheel Speed Sensor
(2)	Front Wheel Speed Sensor Ring

The front wheel speed sensors are of a variable reluctance type. Each sensor is attached to the knuckle assembly in close proximity to a toothed ring. The toothed ring is pressed onto the outer Constant Velocity (CV) joint. As the toothed ring rotates, the wheel speed sensor generates an AC voltage. The magnitude and the frequency are proportional to the speed of the wheel and both will increase with increased speed. The sensor is not repairable nor is the air gap adjustable.

Rear Wheel Speed Sensors and Rings


(1)	Rear Wheel Speed Sensor
(2)	O-Ring
(3)	Brake Drum
(4)	Rear Hub and Bearing Assembly

The rear wheel speed sensors operate in the same manner as the front wheel speed sensors. The rear wheel speed sensors are mounted in the rear suspension knuckles. The rear wheel speed sensor reluctor ring is part of the rear hub and bearing assembly. Replace the rear hub and bearing assembly when the rear wheel speed sensor ring is damaged.

Wheel Speed Sensor Pigtail Harness

Each wheel speed sensor has a pigtail harness made up of a highly flexible twisted pair wiring. Any repair to pigtail harness will result in stiffening and eventual failure due to wire fatigue. For this reason the wheel speed sensor pigtail harness is not repairable and the wheel speed sensor must be replaced. Do not attempt to solder, splice or crimp the wheel speed sensor pigtail harness, as eventual failure will result.

Wiring Harness

The wiring harness is the mechanism by which the BPMV assembly is electrically connected to the following components:

•	The power and ground circuits

•	The wheel speed sensors

•

The fuses

•	The switches

•	The ABS Indicator

•	The Data Link Connector (DLC)

The components considered part of the wiring harness are the wires that provide electrical interconnection and the connectors and/or terminals that provide an electrical and/or mechanical interface from the wire to a component.

ABS Indicator

The ABS indicator turns ON to alert the driver of a malfunction within the system. When the ABS indicator remains ON after the 3 second bulb check the ABS is disabled but normal (non-antilock) braking will remain.

Fuses

The ABS power distribution system consists of fuses and the ignition switch. The fuses consist of the following:

•	The ABS fuse (50A) at the fuse and relay box

•	The STOP fuse (15A)

•	The GAUGE fuse (15A) at the junction block

The fuse and relay box is located on the left hand front of the engine compartment left of the air cleaner. The junction block 1 is located on the lower left hand shroud behind the kick panel.

System Operation

Normal Braking Mode


(1)	Right Rear Flow Control Valve
(2)	Left Front Flow Control Valve
(3)	Left Front ABS Solenoid Valve
(4)	Right Rear ABS Solenoid Valve
(5)	Buffer Chamber
(6)	Proportioning Valve
(7)	Pump Inlet Check Valves
(8)	Left Rear ABS Solenoid Valve
(9)	Right Front ABS Solenoid Valve
(10)	Right Front Flow Control Valve
(11)	Left Rear Flow Control Valve
(12)	Pump Outlet Check Valves
(13)	Master Cylinder

Antilock Braking Mode

An ABS stop occurs when the EBCM determines that one or more wheels are about to lose traction during braking. During an ABS stop the EBCM commands hydraulic pressure reduction at the wheel brake that is about to lose traction. The EBCM activates the solenoid valve for the affected wheel brake hydraulic channel. The solenoid valve triggers the adjoining flow control valve which directs hydraulic pressure into a buffer chamber. The result is a reduction in hydraulic pressure at the wheel brake thus reducing the tendency of wheel slip.

When the wheel is no longer slipping the EBCM deactivates the solenoid valve. This action allows the flow control valve to increase hydraulic pressure at the wheel brake.

This operation continues for all wheels until the wheels are no longer slipping for the duration of the stop. Although the ABS can modulate hydraulic pressure to each wheel brake it cannot increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.

The driver will notice a slight brake pedal pulsation during an ABS stop. This sensation is related to ABS component operation feedback and is considered normal.

System Self Test (Initialization)

The ABS performs a series of tests to the ABS components for proper operation and readiness. The initialization starts when the ignition switch is turned from the LOCK to the ON position. The EBCM turns ON the ABS indicator for 3 seconds. When the ABS indicator turns OFF a slight mechanical noise can be heard. This condition is normal. This noise comes from the BPMV assembly as the EBCM tests solenoid valves and the pump motor.

A slight pulsation may be felt when stepping on the brake pedal while the EBCM is testing the solenoid valves and the pump motor. This condition is considered normal brake pedal feedback.

ABS Indicator Operation

The ABS uses an indicator located in the instrument panel gauge cluster. When turning the ignition switch from the LOCK to the ON position the ABS indicator illuminates for three seconds. If the ABS is operating properly, the indicator turns OFF. If the ABS detects a malfunction, the indicator will stay ON to warn the driver that the ABS is disabled and it needs service.

Tires and ABS

Using the compact spare supplied with the vehicle will not affect the operation of the ABS. The ABS compensates for the smaller compact spare tire. However the driver will notice increased stopping distances due to the reduced size of the compact spare tire.

Replacement Tires

The tire size is important for proper performance of the ABS. When replacing the original tires use the following replacement guidelines:

•	Use a tire of the same size.

•	Use a tire of the same load range.

•	Use a tire with the same construction as the original tires.

Replace the tires in axle sets and only with tires of the same Tire Performance Criteria (TPC) specification number. Use of any other tire size or type may seriously affect the ABS operation.