ABS Description and Operation W/JL4
Vehicles with RPO JL4 are equipped with an EBC 430EV ABS/DRP/TCS/VSES
module.
This module provides the following vehicle performance enhancement systems.
• | Antilock Brake System (ABS) |
• | Dynamic Rear Proportioning (DRP) |
• | Traction Control System (TCS) |
• | Vehicle Stability Enhancement System (VSES) |
The following components are involved in the operation of the above systems.
• | Electronic brake control module (EBCM) - The EBCM controls the system
functions and detects failures. |
| The EBCM contains the following components: |
- | System relay--The system relay is internal to the EBCM. The system
relay is energized when the ignition is ON. The system relay supplies battery positive
voltage to the valve solenoids and to the ABS pump motor. This voltage is referred
to as system voltage. |
- | Solenoids--The solenoids are commanded ON and OFF by the EBCM to
operate the appropriate valves in the brake pressure modulator valve (BPMV). |
- | Longitudinal accelerometer--The EBCM uses the longitudinal accelerometer
to determine the actual straight-line acceleration of the vehicle. |
• | Brake pressure modulator valve (BPMV)--The BPMV uses a 4-circuit
configuration to control hydraulic pressure to each wheel independently. |
| The BPMV contains the following components: |
- | ABS pump motor and pump |
- | Two TC isolation valves |
- | A master cylinder pressure sensor |
- | A front low-pressure accumulator |
- | A rear low-pressure accumulator |
• | Wheel speed sensors (WSS)--As the wheels spin, toothed rings interrupt
magnetic fields in the wheel speed sensors. This causes each wheel speed sensor to
generate an AC signal. The EBCM uses these AC signals to calculate the wheel speed.
Any imperfections in the toothed ring, such as a missing or damaged tooth, can cause
an inaccurate WSS signal. |
• | Traction control switch--VSES and the engine torque reduction function
of TCS are manually disabled or enabled by pressing the traction control switch. |
• | Lateral accelerometer--The EBCM uses the lateral accelerometer to
determine the sideways acceleration of the vehicle. The lateral accelerometer is packaged
with the yaw rate sensor as a single component. |
• | Master cylinder pressure sensor--The master cylinder pressure sensor
is located within the BPMV. The master cylinder pressure sensor uses a 5-volt reference
and generates an output signal proportionate to the hydraulic fluid pressure which
is present in the front brake circuit at the master cylinder. |
• | Yaw rate sensor--The EBCM uses the yaw rate sensor to determine the
rate of rotation along the vehicle's vertical axis. The yaw rate sensor is packaged
with the lateral accelerometer as a single component. |
• | Steering wheel position sensor--The EBCM receives several inputs
from the steering wheel position sensor. Three digital square wave signal inputs are
wired directly to the EBCM harness connector, however, only signals A and B
are used or monitored. The failure of the index pulse signal does not effect VSES
function. The body control module (BCM), which receives an analog steering position
sensor input, transmits steering position data on the serial data line. The EBCM monitors
the serial data information as an added failsafe for the steering position sensor
circuitry. Battery voltage is supplied to the digital portion of the steering wheel
position sensor from the cruise control fuse. The analog portion of the steering wheel
position sensor is supplied a 5-volt reference from the BCM. This circuit is also
used for a lamp dimming function. |
• | Precharge pump motor and pump--The precharge pump assembly is used
to assist the ABS pump in rapidly building hydraulic pressure needed during certain
TCS or VSES events. |
Antilock Brake System (ABS)
When wheel slip is detected during a brake application, an ABS event occurs.
During antilock braking, hydraulic pressure in the individual wheel circuits is controlled
to prevent any wheel from slipping. A separate hydraulic line and specific solenoid
valves are provided for each wheel. The ABS can decrease, hold, or increase hydraulic
pressure to each wheel. The ABS does not, however, increase hydraulic pressure above
the amount which is transmitted by the master cylinder during braking.
During antilock braking, a series of rapid pulsations is felt in the brake pedal.
These pulsations are caused by the rapid changes in position of the individual solenoid
valves as the electronic brake control module (EBCM) responds to wheel speed sensor
inputs and attempts to prevent wheel slip. These pedal pulsations are present only
during antilock braking and stop when normal braking is resumed or when the vehicle
comes to a stop. A ticking or popping noise may also be heard as the solenoid valves
cycle rapidly. During antilock braking on dry pavement, intermittent chirping noises
may be heard as the tires approach slipping. These noises and pedal pulsations are
considered normal during antilock operation.
Vehicles equipped with ABS may be stopped by applying normal force to the brake
pedal. Brake pedal operation during normal braking is no different than that of previous
non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest
stopping distance while maintaining vehicle stability. The typical ABS activation
sequence is as follows.
Pressure Hold
The EBCM closes the isolation valve and keeps the dump valve closed in order
to isolate the slipping wheel when wheel slip occurs. This holds the pressure steady
on the brake so that the hydraulic pressure does not increase or decrease.
Pressure Decrease
If a pressure hold does not correct the wheel slip condition, a pressure decrease
occurs. The EBCM decreases the pressure to individual wheels during deceleration when
wheel slip occurs. The isolation valve is closed and the dump valve is opened. The
excess fluid is stored in the accumulator until the pump can return the fluid to
the master cylinder or fluid reservoir.
Pressure Increase
After the wheel slip is corrected, a pressure increase occurs. The EBCM increases
the pressure to individual wheels during deceleration in order to reduce the speed
of the wheel. The isolation valve is opened and the dump valve is closed. The increased
pressure is delivered from the master cylinder.
Dynamic Rear Proportioning (DRP)
The dynamic rear proportioning (DRP) is a control system that enhances the hydraulic
proportioning function of the mechanical proportioning valve in the base brake system.
The DRP control system is part of the operation software in the electronic brake control
module (EBCM). The DRP uses active control with existing ABS in order to regulate
the vehicle's rear brake pressure.
Traction Control System (TCS)
Traction is maintained by limiting the amount of torque produced by the drivetrain
and also by applying brake pressure to slipping wheels during acceleration. This causes
power to transfer through the driveline to wheels which are not slipping. The transfer
case used on 4 wheel drive vehicles equipped with vehicle stability enhancement
system (VSES) does not contain a viscous coupling and therefore allows the front and
rear driveshafts to turn at substantially different speeds. This front to rear differential
must be kept within acceptable parameters by the VSES. The 2 methods of traction
control are performed as follows.
Engine Torque Reduction
The electronic brake control module (EBCM) uses a 5-volt pulse width modulated
(PWM) signal to request that the powertrain control module (PCM) reduce the amount
of torque to the drive wheels. The PCM reduces torque to the drive wheels by retarding
spark timing and commanding the throttle actuator control. The PCM uses a 12-volt
PWM signal to report to the EBCM the amount of torque that is being delivered to the
drive wheels. Engine torque reduction is mostly used to reduce vehicle speed during
VSES events and during traction control system (TCS) events when the brakes are in
danger of being overheated or when the driven wheels are slipping at the same rate.
Engine torque reduction can be disabled by pressing the traction control switch.
Brake Pressure Application
The EBCM uses brake pressure application to control traction by transferring
torque through the driveline to wheels which are not slipping. The precharge pump
motor, ABS pump motor, and appropriate valve solenoids are commanded ON and OFF to
apply brake pressure to the slipping wheels. Brake pressure application is used in
an attempt to maintain equal wheel speed sensor (WSS) signals at the driven wheels.
The EBCM does not allow excessive brake pressure application due to the fact
that the solenoid coils or the brakes may become overheated, damaging the EBCM or
reducing the driver's ability to stop the vehicle. Estimated coil and brake temperatures
are determined by a calculation in the EBCM software. Overheated solenoid coils cause
all brake pressure application to become disabled and the stability system disabled
message to be displayed. Overheated brakes cause brake pressure application during
TCS events to disable, yet the VSES remains functional and as long as the engine torque
reduction is enabled, there is no indication to the driver when this occurs and no
DTC sets.
Vehicle Stability Enhancement System (VSES)
Vehicle stability enhancement system (VSES) provides added stability during
aggressive maneuvers. Yaw rate is the rate of rotation about the vehicle's vertical
axis. The VSES is activated when the electronic brake control module (EBCM) determines
that the desired yaw rate does not match the actual yaw rate as measured by the yaw
rate sensor.
The desired yaw rate is calculated by the EBCM using, primarily, the following
inputs.
• | The position of the steering wheel |
• | The speed of the vehicle |
• | The lateral, or sideways acceleration of the vehicle |
The difference between the desired yaw rate and the actual yaw rate is the yaw
rate error, which is a measurement of oversteer or understeer. When a yaw rate error
is detected, the EBCM attempts to correct the vehicle's yaw motion by applying brake
pressure to one or more of the wheels. The amount of brake pressure which is applied
varies, depending on the correction required. The engine torque may be reduced also,
if it is necessary to slow the vehicle while maintaining stability.
VSES activations generally occur in turns during aggressive driving. When braking
during VSES activation, the pedal may pulsate. The brake pedal pulsates at a higher
frequency during VSES activation than during ABS activation.
System Pre-Fill
This vehicle is equipped with a 4-wheel disc brake system. Disc brake calipers
are designed so that when hydraulic pressure is not being applied, the caliper piston
lip seal causes the piston to retract, creating measurable clearance between the brake
pads and the rotor. Since a small amount of brake fluid must be delivered to the calipers
before any actual braking occurs, the vehicle stability enhancement system (VSES)
uses system pre-fill to prevent delayed brake application and enhance system performance.
If the electronic brake control module (EBCM) determines that a brake application
is likely to be needed, the ABS pump motor runs momentarily to take up any clearances
between the brake pads and the rotor. By monitoring the master cylinder pressure sensor
feedback signal, the EBCM can determine when the brake pads are contacting the rotor.
The EBCM then holds this small amount of pressure in the system.
A VSES brake application may or may not occur after pre-fill is complete. If
the EBCM determines that a brake application is no longer pending, the pre-fill pressure
is released and the VSES system returns to the normal, monitoring state.
The reason that we must understand system pre-fill is that pre-fill may lead
to customer concerns. Any time the ABS pump motor is active, the motor draws a large
amount of current, and may cause the vehicle lighting systems to dim noticeably. When
ABS activity occurs, most drivers understand that this activity is the cause of noises
and dimming lights. Likewise, when an actual VSES event occurs, the Stability System
Active message is displayed, which helps drivers understand why these other conditions
occur. Since pre-fill is not an actual VSES event, but preparation for a pending event,
no message is displayed. Also, system noise during pre-fill is very minimal. A customer
may become concerned with what is perceived to be an electrical problem, due to the
intermittent dimming lights, when, in fact, no malfunction exists and the condition
is normal.
Precharge Pump
The traction control module (TCS) and vehicle stability enhancement system (VSES)
are dependant on the precharge pump to assist the ABS pump in building hydraulic pressure
to perform brake pressure application. This is because the passages from the master
cylinder reservoir to the ABS pump inlet are restrictive, and do not supply adequate
fluid to the ABS pump. The precharge pump is used mostly at the beginning of brake
pressure applications since once some pressure is built, the ABS pump is usually able
to continue building pressure and maintain the application. The precharge pump inlet
is fed by a flexible hose which draws fluid directly from a port on the master cylinder
reservoir. When the precharge pump is activated, fluid is pumped into the combination
valve, slightly pressurizing the front and rear brake circuits between the master
cylinder and the brake pressure modulator valve (BPMV). It is important to note that
during this time, the electronic brake control module (EBCM) must isolate of the all
wheels, except for those to which the brake pressure application is directed. The
portion of the pressurized fluid that is not drawn into the ABS pump inlet, passes
through the bypass ports in the master cylinder and returns to the reservoir. Some
of the pressurized fluid is supplied to the ABS pump inlet when the EBCM commands
ON a supply valve in the BPMV. Since the fluid at the ABS pump inlet is slightly pressurized,
the ABS pump is able to function with higher efficiency. The precharge pump, however,
is not always used during TCS or VSES events due to the fact that the precharge pump
motor must be protected from overheating. During a long series of brake pressure applications,
the precharge pump may be disabled by the EBCM for up to 12 seconds. Although
the driver may be able to detect a change in the vehicle stability during this time,
the TCS and VSES do remain functional. No indication is given to the driver if the
precharge pump is disabled due to overheating.
Power-Up Self-Test
The electronic brake control module (EBCM) is able to detect many malfunctions
whenever the ignition is ON. However, certain failures cannot be detected unless active
diagnostic tests are performed on the components. Shorted solenoid coil or motor windings,
for example, cannot be detected until the components are commanded ON by the EBCM.
Therefore, a power-up self-test is required at the beginning of each ignition cycle
to verify correct operation of components before the various control systems can be
enabled. The EBCM performs the first phase of the power-up self-test when the ignition
is first turned ON. The system relay, solenoids and the ABS pump motor are commanded
ON and OFF to verify proper operation and the EBCM verifies the ability to return
the system to base braking in the event of a failure. The master cylinder pressure
sensor performs a self-test by sending a series of specific voltage signals to the
EBCM, each for a predetermined amount of time. This phase of the power-up self-test
may be heard by the driver, depending on how soon the engine is cranked and started
after turning ON the ignition. The second phase of the power-up self-test begins when
the vehicle is driven at a speed greater than 16 km/h (10 mph) and the
EBCM has not detected any traction control module (TCS)/vehicle stability enhancement
system (VSES) related malfunctions thus far. During this phase, the precharge pump
is tested to verify the ability to build adequate pressure to perform brake pressure
application during certain TCS and VSES events. When the brake switch indicates that
the brake is not applied and the master cylinder pressure is detected as being low,
the EBCM proceeds with the test. The EBCM isolates all of the wheels by closing the 4 isolation
valves. The precharge pump is then commanded ON while the EBCM monitors the master
cylinder pressure sensor input. The precharge pump must build approximately 248 kPa
(36 psi) of hydraulic pressure within 1 second or the test is failed.
If the EBCM uses brake pressure application to perform TCS or VSES prior to the second
phase of the power-up self-test, the precharge pump is tested at this time and the
second phase of the test is not required. Due to the fact that all of the wheels are
isolated during the second phase of the test, the test must be aborted if the brake
is applied while the test is being performed. Occasionally, the driver may detect
this by experiencing a momentary hard pedal.
VSES Sensors Initialization
The vehicle stability enhancement system (VSES) sensors values may vary slightly
due to differences in temperature, sensor mounting, connector resistances, manufacturing,
etc. Since VSES is a very sensitive and precise control system, it is imperative that
the electronic brake control module (EBCM) be able to accurately equate a given sensor
voltage with an actual unit of measurement. For example, the yaw rate signal of one
vehicle may be 2.64 volts at +18.0 deg/sec yaw rate while the yaw rate
signal of another vehicle may be 2.64 volts at +17.5 deg/sec yaw rate.
Therefore, at the beginning of each ignition cycle, the EBCM must perform an initialization
procedure to observe how the VSES sensors are correlated with each other and also
to determine what each sensor value is when the applicable unit of measurement equals
0. This voltage is referred to as the sensor bias voltage. Although some activation
of the VSES system may occur if required to prior to full initialization, the system
does not give optimum performance until the sensors are fully initialized.
The following VSES sensors require initialization:
• | The lateral accelerometer |
• | The longitudinal accelerometer |
• | The master cylinder pressure sensor |
• | The steering wheel position sensor |
When the vehicle speed is greater than 25 km/h (15 mph), full
sensor initialization must occur during 3 km (1.8 mi) of driving or
1 km (0.6 mi) of straight and stable driving, whichever occurs first.
Although an attempt at initialization may fail due to driving conditions, such as
driving on a very winding road, failed initialization is usually caused by a sensor
bias voltage which is not within an acceptable range. Often, a DTC sets soon after
a failed initialization attempt. The message center displays the stability system
disabled message when sensor initialization fails.
ECE 13 Response
The electronic brake control module (EBCM) illuminates the ABS indicator when
a malfunction which disables ABS is detected. Usually, the ABS indicator is turned
OFF during the following ignition cycle unless the fault is detected during that ignition
cycle. However, the setting of a wheel speed sensor related DTC causes the ABS indicator
to remain illuminated during the following ignition cycle until the vehicle is operated
at a speed greater than 13 km/h (8 mph). This allows the EBCM to verify
that no malfunction exists, before turning OFF the ABS indicator. This reaction occurs
even if the ABS indicator turns OFF when the scan tool is used to clear the DTCs.
When repairing these vehicles, it is important to ensure that the ECE 13 response
has occurred and that the ABS indicator does not illuminate after returning the vehicle
to the customer. It is also important to verify that ECE 13 is not the cause
of an ABS indicator which is illuminated when no DTCs are set, before attempting to
diagnose other possible causes.
Driver Information Indicators and Messages
The following indicators are used to inform the driver of several different
factors.
Brake Warning Indicator
The instrument panel cluster (IPC) illuminates the brake warning indicator when
the following occurs.
• | The body control module (BCM) detects that the park brake is engaged.
The IPC receives a serial data message from the BCM requesting illumination. The
brake warning indicator flashes at a rate of approximately twice per second when the
park brake is engaged. |
• | The electronic brake control module (EBCM) detects a low brake fluid condition
or a base brake pressure differential and sends a serial data message to the IPC
requesting illumination. |
• | The IPC performs the bulb check. |
• | The EBCM detects an ABS-disabling malfunction which also disables dynamic
rear proportioning (DRP) and sends a serial data message to the IPC requesting illumination. |
ABS Indicator
The IPC illuminates the ABS indicator when the following occurs.
• | The EBCM detects an ABS-disabling malfunction and sends a serial data
message to the IPC requesting illumination. |
• | The IPC performs the bulb check. |
• | The IPC detects a loss of serial data communication with the EBCM. |
• | A DTC is set during the previous ignition cycle which requires an ECE 13
response at the beginning of the current ignition cycle. The EBCM sends a serial data
message to the IPC requesting illumination. |
Stability System Caution Indicator
The IPC illuminates the stability system caution indicator when one or more
of the following conditions exists.
• | A traction control system (TCS) or vehicle stability enhancement system
(VSES) event occurs. The EBCM sends a serial data message to the IPC requesting that
the stability system caution indicator be flashed ON and OFF. |
• | The driver manually disables the VSES and engine torque reduction by pressing
the traction control switch. The EBCM sends a serial data message to the IPC requesting
illumination. |
• | The estimated temperature of any solenoid coil exceeds an acceptable limit.
The EBCM sends a serial data message to the IPC requesting illumination. |
• | The EBCM detects a failed brake switch. The EBCM sends a serial data message
to the IPC requesting this display. A DTC sets when this condition exists. |
• | The EBCM detects that the brake fluid level is low or a base brake pressure
differential exists. These 2 conditions are not distinguishable by the EBCM.
The EBCM sends a serial data message to the IPC requesting this display. |
• | Serial data communication between the EBCM and any of several other control
modules is interrupted. The EBCM sends a serial data message to the IPC requesting
illumination or the IPC displays the indicator when communication with the EBCM is
interrupted. |
• | The PCM is not able to perform engine torque reduction. The EBCM sends
a serial data message to the IPC requesting illumination. DTCs set when this condition
exists. |
• | The EBCM detects an excessively low or excessively high ignition voltage.
The EBCM sends a serial data message to the IPC requesting illumination. |
• | The EBCM sets any one of many VSES-disabling DTCs. The EBCM sends a serial
data message to the IPC requesting illumination. |
Stability System Not Ready Indicator
The IPC illuminates the stability system not ready indicator when the VSES has
failed to initialize in an acceptable amount of time. The EBCM sends a serial data
message to the IPC requesting illumination.
ABS Description and Operation W/O JL4
This vehicle is equipped with an EBC 325EV ABS/DRP module.
This module provides the following vehicle performance enhancement systems:
• | Antilock Brake System (ABS) |
• | Dynamic Rear Proportioning (DRP) |
The following components are involved in the operation of the above systems:
• | Electronic brake control module (EBCM)--The EBCM controls the system
functions and detects failures. |
| The EBCM contains the following components: |
- | System relay--The system relay is internal to the EBCM. The system
relay is energized when the ignition is ON. The system relay supplies battery positive
voltage to the valve solenoids and to the ABS pump motor. This voltage is referred
to as system voltage. |
- | Solenoids--The solenoids are commanded ON and OFF by the EBCM to
operate the appropriate valves in the brake pressure modulator valve (BPMV). |
• | Brake pressure modulator valve (BPMV)--The BPMV uses a 3-circuit
configuration to control hydraulic pressure to each front wheel independently, and
to the rear wheels as a pair. |
| The BPMV contains the following components. |
- | ABS pump motor and pump |
- | A front low-pressure accumulator |
- | A rear low-pressure accumulator |
• | Wheel speed sensors (WSS)--As the wheels spin, toothed rings interrupt
magnetic fields in the wheel speed sensors. This causes each WSS to generate an AC
signal. The EBCM uses these AC signals to calculate the wheel speed. Any imperfections
in the toothed ring, such as a missing or damaged tooth, can cause an inaccurate
WSS signal. |
Antilock Brake System (ABS) Operation
When wheel slip is detected during a brake application, an ABS event occurs.
During antilock braking, hydraulic pressure in the individual wheel circuits is
controlled to prevent any wheel from slipping. A separate hydraulic line and specific
solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase
hydraulic pressure to each wheel. The ABS does not, however, increase hydraulic pressure
above the amount which is transmitted by the master cylinder during braking.
During antilock braking, a series of rapid pulsations is felt in the brake
pedal. These pulsations are caused by the rapid changes in position of the individual
solenoid valves as the electronic brake control module (EBCM) responds to wheel speed
sensor inputs and attempts to prevent wheel slip. These pedal pulsations are present
only during antilock braking and stop when normal braking is resumed or when the
vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid
valves cycle rapidly. During antilock braking on dry pavement, intermittent chirping
noises may be heard as the tires approach slipping. These noises and pedal pulsations
are considered normal during antilock operation.
Vehicles equipped with ABS may be stopped by applying normal force to the brake
pedal. Brake pedal operation during normal braking is no different than that of previous
non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest
stopping distance while maintaining vehicle stability. The typical ABS activation
sequence is as follows:
Pressure Hold
The EBCM closes the isolation valve and keeps the dump valve closed in order
to isolate the slipping wheel when wheel slip occurs. This holds the pressure steady
on the brake so that the hydraulic pressure does not increase or decrease.
Pressure Decrease
If a pressure hold does not correct the wheel slip condition, a pressure decrease
occurs. The EBCM decreases the pressure to individual wheels during deceleration
when wheel slip occurs. The isolation valve is closed and the dump valve is opened.
The excess fluid is stored in the accumulator until the pump can return the fluid
to the master cylinder or fluid reservoir.
Pressure Increase
After the wheel slip is corrected, a pressure increase occurs. The EBCM increases
the pressure to individual wheels during deceleration in order to reduce the speed
of the wheel. The isolation valve is opened and the dump valve is closed. The increased
pressure is delivered from the master cylinder.
Dynamic Rear Proportioning (DRP) Operation
The dynamic rear proportioning (DRP) is a control system that enhances the hydraulic
proportioning function of the mechanical proportioning valve in the base brake system.
The DRP control system is part of the operation software in the electronic brake control
module (EBCM). The DRP uses active control with existing ABS in order to regulate
the vehicle's rear brake pressure.
Power-Up Self-Test
The electronic brake control module (EBCM) is able to detect many malfunctions
whenever the ignition is ON. However, certain failures cannot be detected unless
active diagnostic tests are performed on the components. Shorted solenoid coil or
motor windings, for example, cannot be detected until the components are commanded
ON by the EBCM. Therefore, a power-up self-test is required at the beginning of each
ignition cycle to verify correct operation of components before the various control
systems can be enabled. The EBCM performs the power-up self-test when the ignition
is first turned ON. The system relay, solenoids and the ABS pump motor are commanded
ON and OFF to verify proper operation and the EBCM verifies the ability to return
the system to base braking in the event of a failure. The power-up self-test may be
heard by the driver, depending on how soon the engine is cranked and started after
turning ON the ignition.
ECE 13 Response
The electronic brake control module (EBCM) illuminates the ABS indicator when
a malfunction which disables ABS is detected. Usually, the ABS indicator is turned
OFF during the following ignition cycle unless the fault is detected during that
ignition cycle. However, the setting of a most wheel speed sensor related DTC causes
the ABS indicator to remain illuminated during the following ignition cycle until
the vehicle is operated at a speed greater than 13 km/h (8 mph) or,
occasionally, 64 km/h (40 mph), depending on which DTC sets. This allows
the EBCM to verify that no malfunction exists, before turning OFF the ABS indicator.
It is important to verify that ECE 13 is not the cause of an ABS indicator
which is illuminated when no DTCs are set, before attempting to diagnose other possible
causes.
Driver Information Indicators and Messages
The following indicators are used to inform the driver of several different
factors:
Brake Warning Indicator
The instrument panel cluster (IPC) illuminates the brake warning indicator
when the following occurs:
• | The body control module (BCM) detects that the park brake is engaged.
The IPC receives a serial data message from the BCM requesting illumination. The
brake warning indicator flashes at a rate of approximately twice per second when
the park brake is engaged. |
• | The electronic brake control module (EBCM) detects a low brake fluid condition
or a base brake pressure differential and sends a serial data message to the IPC
requesting illumination. |
• | The IPC performs the bulb check. |
• | The EBCM detects an ABS-disabling malfunction which also disables dynamic
rear proportioning (DRP) and sends a serial data message to the IPC requesting illumination. |
ABS Indicator
The IPC illuminates the ABS indicator when the following occurs:
• | The EBCM detects an ABS-disabling malfunction and sends a serial data
message to the IPC requesting illumination. |
• | The IPC performs the bulb check. |
• | The IPC detects a loss of serial data communication with the EBCM. |
• | A DTC is set during the previous ignition cycle which requires an ECE 13
response at the beginning of the current ignition cycle. The EBCM sends a serial
data message to the IPC requesting illumination. |