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.
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
12 km/h (7.5 mph) and the EBCM has not detected any traction control module (TCS)/vehicle
stability enhancement system (VSES) related malfunctions thus far. 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. 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
2008 Chevrolet Silverado 1500
2008 BRAKES Antilock Brake System - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado