Chevrolet Silverado / GMC Sierra. Service manual — part 730

IPC displays the message when communication with the EBCM is interrupted.

The PCM is not able to perform engine torque reduction. The EBCM sends a GMLAN
message to the IPC requesting this display. DTCs set when this condition exists.

The EBCM detects an excessively low or excessively high ignition voltage. The EBCM
sends a GMLAN message to the IPC requesting this display.

Service Stabilitrak Message

The message center displays the service stability system message when any one of many VSES-
disabling DTCs is set. The EBCM sends a serial data message to the IPC requesting this display.

Service Traction Control Message

The message center displays the service traction control system message when any one of many
traction control - disabling DTCs is set. The EBCM sends a serial data message to the IPC
requesting this display.

ABS DESCRIPTION AND OPERATION (WITHOUT JL4)

This vehicle is equipped with an EBC 345 ABS/EBD module.

This module provides the following vehicle performance enhancement systems.

Antilock Brake System (ABS)

Electronic Brake Distribution (EBD)

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.

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

The BPMV contains the following components.

ABS pump motor and pump

Three isolation valves

Three dump valves

A front low-pressure accumulator

A rear low-pressure accumulator

Wheel speed sensors (WSS)-EBCM sends a 12-volt reference voltage signal to each front
wheel speed sensor. As the wheel spins, the wheel speed sensor produces a square wave DC
signal voltage. The wheel speed sensor increases the signal frequency as the wheel speed
increases, but does not increase the signal amplitude.

Antilock Brake System (ABS) Operation

When wheel slip is detected during a brake application, an antilock brake system (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.

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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.

Electronic Brake Distribution (EBD) Operation

The electronic brake distribution (EBD) is a control system that replaces the hydraulic
proportioning function of the mechanical proportioning valve in the base brake system. The EBD
control system is part of the operation software in the electronic brake control module (EBCM).
The EBD uses active control with existing antilock brake system (ABS) in order to regulate the
vehicle 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 antilock brake system
(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 antilock brake system (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 may cause the ABS indicator to

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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 body control module (BCM) 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 antilock brake system (ABS)-disabling malfunction which also
disables electronic brake distribution (EBD) and sends a serial data message to the IPC
requesting illumination.

ABS Indicator

The IPC illuminates the ABS indicator when the following occurs.

The electronic brake control module (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.

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

2008 Chevrolet Silverado 1500

2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado