GM: Electra/Park Avenue/Ninety-Eight 1990-1993

General Description

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The Teves mk iv systems used on 1991-1993 vehicles. The system allows individual modulation of braking force at each wheel as well as providing traction control at the drive wheels if the vehicle is so equipped. The abs system employs a conventional diagonally-split braking system and additional abs components. The system allows the operator to maintain directional control during heavy braking situations by preventing locked-wheel skidding.

On vehicles equipped with the Traction Control System (tcs), wheel spin at the drive wheels is reduced by selective application of the wheel brakes if vehicle speed is below 25 mph (40 km/h). The tcs system is designed to improve traction on loose or wet surfaces and aid in getting the vehicle moving from rest.

SYSTEM OPERATION



Anti-Lock System

Braking is performed by the conventional brake system until the Electronic Brake Control Module (ebcm) detects a wheel beginning to lock or the brake pedal has traveled beyond a specified limit. The ebcm will then command the system into anti-lock mode.

Electric signals are received by the ebcm from each wheel speed sensor. By comparing these signals to each other and to pre-programmed values, the ebcm can determine that one or more wheels is approaching lock-up. The ebcm activates the Pressure Modulator Valve (pmv) to control fluid pressure to the wheels. The pmv assembly has 2 valves per hydraulic circuit; the ebcm operates these valves electrically to control brake pressure. The valves may be placed into 3 modes: pressure increase, pressure reduce or pressure hold. By switching rapidly between these 3 modes, the ebcm can reduce pressure at the locking wheel, slow the most rapid wheel to the average or maintain the wheels just below the point of lock-up.

During the pressure increase mode, the inlet valve within the pmv is open, allowed to enter the particular hydraulic circuit. As this mode cycles, pressure and fluid is reduced within the master cylinder, causing the brake pedal to drop nearer the floor. When the pedal travel exceeds a pre-determined level, the ebcm will activate the pmv pump motor. Pump pressure is applied to the wheel circuit(s) in need and/or the master cylinder hydraulic circuits. With pressure applied to the master cylinder hydraulic circuits, the pedal will rise until the brake travel switch is de-activated, switching the pump off.

During vehicle operation, the ebcm performs a series of self-tests, checking both electronic and hydraulic systems for vaults. If detectable problems exist, the ebcm will set a fault code and/or illuminate the antilock dash warning lamp. The antilock warning lamp is in addition to the normal brake warning lamp which warns of problems in the conventional brake system.

Traction Control System (TCS)

The traction control system is additional to the abs system and is not found on all vehicles with abs. With traction control, brake pressure is increased to reduce wheel spin; with abs, line pressure is reduced to allow greater wheel spin. The ebcm monitors the speed of the drive wheels through the wheel speed sensors; if wheel slip is detected below 25 mph with the brakes not applied, the ebcm enters the traction control mode.

Once in traction control mode, the ebcm commands two isolation valves in the pmv into operation. The isolation valves close to separate the non-driven wheels and the master cylinder circuits from the drive wheels. Once isolated, brake fluid pressure may be applied to the drive wheels without affecting the other circuits. The ebcm turns on the pmv pump motor and begins cycling the inlet and outlet valves to slow the slipping wheel(s).

Since the pump motor supplies more fluid than required, two pressure relief valves allow excess fluid to r