Dodge Nitro. Manual — part 220

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 STABILITY PROGRAM (ESP)

The ESP system enhances directional control and stability of the vehicle under various driving conditions. ESP
corrects 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 appropriate 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 optimum 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 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 deceleration, 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.

OPERATION

ANTILOCK BRAKE SYSTEM (ABS)

There are a few performance characteristics of the MK25e anti-lock brake system that may, at first, seem
abnormal but in fact are normal. These characteristics are described below.

NORMAL BRAKING

2007 Dodge Nitro R/T

2007 BRAKES ABS Service Information - Nitro

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

ABS BRAKING

ABS operation is available at all vehicle speeds above 5-8 km/h (3-5 mph). If a wheel locking tendency is
detected during brake application, the brake system enters ABS mode. During ABS braking, hydraulic pressure
in the four wheel circuit is modulated to prevent any wheel from locking. Each wheel circuit is designed with a
set of electronic solenoids to allow brake pressure to be modulated at each wheel individually. For vehicle
stability reasons, both rear wheel solenoids receive the same electrical signal input during ABS. Wheel lock-up
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 brake pressure at all four 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 each wheel is the same and does not exceed the pressure appropriate for the
wheel with the highest slip in order to maintain vehicle stability.

ELECTRONIC STABILITY PROGRAM (ESP)

To determine whether the car is responding properly to cornering commands, ESP uses steering wheel angle,
yaw (turning) rate and lateral acceleration sensors (combined into Dynamics Sensor). Using signals from these
sensors, in addition to individual wheel speed sensor signals, the system determines appropriate brake and
throttle actions. Once initiated, ESP operates much like All-Speed Traction Control, except that the goal is
directional stability. If the vehicle yaw response, or rate of turning, is inconsistent with the steering angle and
vehicle speed indications, the ESP system applies the brakes and, if necessary closes the throttle, to restore
control. This occurs whether the vehicle is turning too rapidly (oversteering) or not rapidly enough
(understeering).

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 5-8 km/h (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

2007 Dodge Nitro R/T

2007 BRAKES ABS Service Information - Nitro

designed with a set of electric solenoids 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).

NOISE AND 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 5-6 km/h (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 5 km/h (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

2007 Dodge Nitro R/T

2007 BRAKES ABS Service Information - Nitro

(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
replacement 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 modulates 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 pressure to make the transition smooth, while maintaining forward progress. By reducing engine
power, braking effectiveness is maintained and the system can operate throughout the normal vehicle speed
range. That is why the system is identified as providing "all-speed" traction control.

With AWD, where front-wheel slip can occur, the degree of throttle intervention is relatively less than with
rear-wheel drive. The difference in speed capability and the degree of throttle intervention between rear-wheel
drive and all-wheel drive is due to the fact that non-driven front wheels on a rear-wheel drive vehicle give the
system an accurate vehicle speed reference on which to base responses. With AWD, the possibility that the
front wheels may also be slipping makes appropriate corrective action more difficult to determine, thus limiting
the effective speed range. Offsetting this is the fact that loss of traction is less likely with AWD because torque
is transmitted through all four wheels to begin with. In actual driving situations on snow or ice, the rear-wheel
drive and AWD systems respond in essentially the same way up to the 45 mph (72 km/h) limit of the AWD

2007 Dodge Nitro R/T

2007 BRAKES ABS Service Information - Nitro