System Description

TEVES MARK 20e SYSTEM DESCRIPTION
This information covers the physical and operational descriptions, and the diagnostic service procedures for the Teves Mark 20e Antilock Brake System. It is the only antilock brake system (ABS) available on this vehicle.

The purpose of the antilock brake system is to prevent wheel lockup under braking conditions on virtually any type of road surface. Antilock braking is desirable because a vehicle that is stopped without locking the wheels retains directional stability and some steering capability. This allows the driver to retain greater control of the vehicle during braking.

All vehicles equipped with ABS use Electronic Variable Brake Proportioning (EVBP) to balance front-to-rear braking when the brakes are applied in the partial braking range.

A Controller Antilock Brake (CAB) module is used to monitor wheel speeds and to modulate (control) hydraulic pressure in each brake channel when ABS is actuated. The CAB also provides a vehicle speed signal (VSS) to the powertrain control module via PCI BUS.

During a non-ABS stop, the system functions as a standard diagonally split configuration. The primary hydraulic system supplies brake fluid pressure to the right front and left rear brakes, and the secondary hydraulic system supplies the right rear and left front brakes. A conventional proportioning valve is not used. This system uses the existing ABS solenoids to replace and perform the same functions that the proportioning valves do. The CAB has a special software program that monitors the wheel speeds and when certain criteria are met the software will enable the solenoids to perform the same brake fluid management control as the proportioning valves.

During an ABS stop, the system still uses the diagonal hydraulic split; however, the brake system pressure is further split into four control channels. During ABS operation, all wheels are controlled independently and are on four separate control channels.

During an antilock stop, "wheel lock-up" does not necessarily mean that the wheel has locked, it means only that the wheel is turning slower than the vehicle speed. This is called "wheel slip" and is indicated as a percentage. 0% slip means that the wheel is rolling free and 100% slip means that the wheel is locked. The antilock system maintains an average of approximately 20% wheel slip.

It is important to remember that the antilock brake system does not shorten the vehicle stopping distance under all driving conditions, but provides improved control of the vehicle while stopping. Vehicle stopping distance is still dependent on vehicle speed, weight, tires, road surface, and other factors.

PEDAL FEEL/VEHICLES CHARACTERISTICS
There are several pedal feel/vehicle characteristics that are considered normal for antilock braking that may require further explanation.

When stopping conditions activate the antilock brakes, the driver may feel some vibrations/ pulsations in the brake pedal and may hear the solenoid valves clicking and the pump motor running. The vibrations/pulsations are caused by the isolating, building and decaying of brake fluid pressure within the brake lines. The ABS system prevents complete wheel lock-up, but some wheel slip is required for the best braking performance. This slip may result in some tire chirping, depending on the road surface. This chirping should not be interpreted as total wheel lock-up. Total wheel lock-up leaves black tire marks on dry pavement. Antilock braking may leave some light marks.

At the end of an ABS stop, the ABS may function all the way down to near O km/in (O mph). There may be a slight brake pedal drop anytime the ABS is deactivated.

In case of braking on a bumpy surface, the ABS system may detect wheel locking tendencies due to wheel hop and cycle the ABS. In that event the brake pedal may pulsate with a perceived loss of deceleration. ABS braking may also be activated at times while on dry pavement with sand, gravel? or other loose debris on the road.

It should be noted that the pulsating pedal feel characteristic will not illuminate the brake warning lamps or set a trouble code that is stored in the Controller Antilock Brake (CAB). When investigating a hard pedal feel, inspect the sensor and tone wheel teeth for chips/broken teeth, damaged sensor pole tips, excessive runout of the tone wheel, or excessive air gap.