This vehicle uses the Continental Teves MK25e elec-
tronic brake control system. The system includes ABS
(Anti-lock Brake System), EVBP (Electronic Variable
Brake Proportioning), TCS (Traction Control System),
BAS (Brake Assist System), ERM (Electronic Roll Mit-
igation) and ESP (Electronic Stability Program). All six
systems work together to enhance vehicle stability and
control in various driving conditions and are commonly
referred to as ESP. ESP is standard

The electronic brake control system uses the following
components to operate:

•

Integrated Control Unit (ICU) – The ICU is a
combination of the Electronic Brake Controller
(EBC) and the Hydraulic Control Unit (HCU) (4)

•

Wheel Speed Sensors (WSS) - Four sensors
(one at each wheel)

•

Dynamics

Sensor

–

The

Dynamics

Sensor

includes a yaw rate sensor, (The Dynamics Sen-
sor is located under the center console near the
center of the vehicle).

•

lateral accelerometer and, on 4x4 vehicles with a low range transfer case (245 T-Case), a longitudinal accel-
erometer.

•

Steering Angle Sensor (SAS) – The SAS is part of the clock spring assembly in the steering column.

•

Brake Pressure Sensor – The brake pressure sensor is located in the HCU and is not serviceable separate
from the HCU.

•

ALL-SPEED TRACTION CONTROL

The TCS is an all-speed traction control system that functions up to the maximum allowed vehicle speed. TCS
enhances vehicle stability and mobility by reducing wheel spin when accelerating on slippery surfaces. TCS controls
wheel spin by applying the brakes and/or reducing engine power.

ANTILOCK BRAKE SYSTEM (ABS)

The purpose of the antilock brake system (ABS) 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

ELECTRONIC VARIABLE BRAKE PROPORTIONING

Vehicles equipped with ABS use EVBP to balance front-to-rear braking. The EVBP is used in place of a rear brake
proportioning valve. The EVBP system controls the slip of the rear wheels during braking at low to moderate decel-
eration, up until the point where ABS control is necessary. The brake pressure at the rear wheels is controlled by
using the inlet and outlet valves located in the hydraulic control unit (HCU).

EVBP activation should not be perceptible by the customer because there is no pump motor noise and almost no
brake pedal feedback.

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ELECTRONIC STABILITY PROGRAM

The ESP system enhances directional control and stability of the vehicle under various driving conditions. ESP cor-
rects for over/under steering of the vehicle by applying the brake of the appropriate wheel to assist in counteracting
the over/under steer condition. Engine power may also be reduced to help the vehicle maintain the desired path.
ESP uses sensors in the vehicle to determine the vehicle path intended by the driver and compares it to the actual
path of the vehicle. When the actual path does not match the intended path, ESP applies the brake of the appro-
priate wheel to assist in counteracting the oversteer or understeer condition

•

Oversteer – when the vehicle is turning more than appropriate for the steering wheel position.

•

Understeer – when the vehicle is turning less than appropriate for the steering wheel position.

The “ESP/TCS Indicator Light” located in the instrument cluster, starts to flash as soon as the tires lose traction and
the ESP system becomes active. The “ESP/TCS Indicator Light” also flashes when TCS is active.

BRAKE ASSIST SYSTEM (BAS)

The BAS is designed to optimize the vehicle’s braking capability during emergency braking maneuvers. The system
detects an emergency braking situation by sensing the rate and amount of brake application and then applies opti-
mum pressure to the brakes. This can help reduce braking distances. The BAS complements the antilock brake
system (ABS). Applying the brakes very quickly results in the best BAS assistance.

ELECTRONIC ROLL MITIGATION (ERM)

This system anticipates the potential for wheel lift by monitoring the driver’s steering wheel input and the speed of
the vehicle. When ERM determines that the rate of change of the steering wheel angle and vehicles speed are
sufficient to potentially cause wheel lift, it applies the appropriate brake and may reduce engine power to lessen the
chance that wheel lift will occur. ERM will only intervene during very severe or evasive driving maneuvers.

ERM can only reduce the chance of wheel lift occurring during severe or evasive driving maneuvers. It can not
prevent wheel lift due to other factors such as road conditions, leaving the roadway or striking objects or other
vehicles.

OPERATION

ANTILOCK BRAKE SYSTEM WITH TRACTION CONTROL

ABS

There are a few performance characteristics of the MK25E Antilock Brake System that may at first seem abnormal,
but in fact are normal. These characteristics are described below.

NORMAL BRAKING

Under normal braking conditions, the ABS functions the same as a standard base brake system with a diagonally
split master cylinder and conventional vacuum assist.

ABS BRAKING

ABS operation is available at all vehicle speeds above 3–5 mph. If a wheel locking tendency is detected during a
brake application, the brake system enters the ABS mode. During ABS braking, hydraulic pressure in the four wheel
circuits is modulated to prevent any wheel from locking. Each wheel circuit is designed with a set of electric sole-
noids to allow modulation, although for vehicle stability, both rear wheel solenoids receive the same electrical signal.
Wheel lockup may be perceived at the very end of an ABS stop and is considered normal.

During an ABS event, the integrated control unit (ICU) regulates hydraulic pressure at all 4 of the vehicle’s wheels.

The hydraulic pressure at each front wheel is controlled independently (relative to the amount of slip at each wheel)
in order to maximize the braking force generated by the front brakes. The rear wheels are controlled such that the
hydraulic pressure at either rear wheel does not exceed that of the highest slip rear wheel in order to maintain
vehicle stability.

The system can build and release pressure at each wheel, depending on signals generated by the wheel speed
sensors (WSS) at each wheel and received at the Antilock Brake Module (ABM).

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BRAKES - ABS SERVICE INFORMATION

NOISE AN BRAKE PEDAL FEEL

During ABS braking, some brake pedal movement may be felt. In addition, ABS braking will create ticking, popping,
or groaning noises heard by the driver. This is normal and is due to pressurized fluid being transferred between the
master cylinder and the brakes. If ABS operation occurs during hard braking, some pulsation may be felt in the
vehicle body due to fore and aft movement of the suspension as brake pressures are modulated.

At the end of an ABS stop, ABS is turned off when the vehicle is slowed to a speed of 3–4 mph. There may be a
slight brake pedal drop anytime that the ABS is deactivated, such as at the end of the stop when the vehicle speed
is less than 3 mph or during an ABS stop where ABS is no longer required. These conditions exist when a vehicle
is being stopped on a road surface with patches of ice, loose gravel, or sand on it. Also, stopping a vehicle on a
bumpy road surface activates ABS because of the wheel hop caused by the bumps.

TIRE NOISE AND MARKS

Although the ABS system prevents complete wheel lockup, some wheel slip is desired in order to achieve optimum
braking performance. Wheel slip is defined as follows: 0 percent slip means the wheel is rolling freely and 100
percent slip means the wheel is fully locked. During brake pressure modulation, wheel slip is allowed to reach up to
25–30 percent. This means that the wheel rolling velocity is 25–30 percent less than that of a free rolling wheel at
a given vehicle speed. This slip may result in some tire chirping, depending on the road surface. This sound should
not be interpreted as total wheel lockup.

Complete wheel lockup normally leaves black tire marks on dry pavement. The ABS will not leave dark black tire
marks since the wheel never reaches a fully locked condition. However, tire marks may be noticeable as light
patched marks.

START-UP AND DRIVE-OFF CYCLES

When the ignition is turned on, a popping sound and a slight brake pedal movement may be noticed. The ABS
warning lamp will also be on for up to 5 seconds after the ignition is turned on.

When the vehicle is first driven off, a humming may be heard or felt by the driver at approximately 12–25 mph
(20–40 km/h). All of these conditions are a normal function of ABS as the system is performing a diagnosis check.

PREMATURE ABS CYCLING

Symptoms of premature ABS cycling include: clicking sounds from the solenoid valves; pump/motor running; and
pulsations in the brake pedal. Premature ABS cycling can occur at any braking rate of the vehicle and on any type
of road surface. Neither the red BRAKE indicator lamp, nor the amber ABS indicator lamp, illuminate and no fault
codes are stored in the ABM.

Premature ABS cycling is a condition that needs to be correctly assessed when diagnosing problems with the
antilock brake system. It may be necessary to use a scan tool to detect and verify premature ABS cycling.

Check the following common causes when diagnosing premature ABS cycling: damaged wheel bearings (causing
tone wheel issues); damaged wheel bearing housings where wheel speed sensors mount; and loose wheel speed
sensor mounting bolts.

After diagnosing the defective component, repair or replace it as required. When the component repair or replace-
ment is completed, test drive the vehicle to verify that premature ABS cycling has been corrected.

ALL-SPEED TRACTION CONTROL

Traction control systems sense impending wheel spin based on a model of the rate of change of wheel speed under
normal traction conditions. The All-Speed Traction Control uses signals from the same wheel speed sensors as ABS
to determine when to apply the brakes to one or more wheels and when to reduce engine torque output using the
electronic throttle control (ETC) to prevent wheel slip during acceleration. Throttle control makes the vehicle less
reliant on brake application alone to maintain traction, increasing the operating speed range and more closely mod-
ulates speed, resulting in smoother operation. With All-Speed Traction Control reducing engine torque as well as
applying the brakes, it is possible to achieve almost seamless torque application at the wheels.

If the wheel slip is severe enough to require throttle intervention, All-Speed Traction Control will reduce engine
torque and sometimes upshift the transmission to avoid the condition. In milliseconds, All-Speed Traction Control
interrogates the engine control system to determine the current torque output, determines how much the torque
output the current conditions will allow, and signals this requirement to the engine control system, which reduces the
torque by partially closing the throttle. With execution of the torque reduction, the brake system reduces brake pres-

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