Sprinter 3500 L5-2.7L DSL Turbo (2004)
close the BLS circuit and the BLS Output circuit supplies 12 volts at the CAB. When the driver releases the brake pedal, the BLS Output circuit
voltage drops to 0 volts and the CAB senses the brake pedal state. This tells the CAB what position the brake pedal is currently in to make an ABS
event possible. When using the DRBIII in Inputs/ Outputs, the BS and BLS will read opposite switch states. Note: The BS and BLS are in the same
switch housing.
TRACTION CONTROL SYSTEM SWITCH (TCSS): This switch signals the CAB to either turn ON or OFF the TCS. The driver can toggle the
TCSS, which receives 12 volts from the D (+) Relay Output circuit. Depending on the position of the TCSS, open or closed, the CAB receives the
TCSS state voltage on the TCS Switch Sense circuit. When 12 volts are applied to the TCS Switch Sense circuit, the TCS is OFF. When no voltage is
present, the TCS is ON.
WHEEL SPEED SENSORS AND TONE WHEELS: The Bosch 5.7 system uses one passive WSS on each wheel. The sensor measures the wheel
speed by monitoring a rotating tone wheel. As the teeth of the tone wheel move through the magnetic field of the sensor an AC voltage and amperage
is generated. This signal frequency increases or decreases proportionally to the speed of the wheel. The CAB monitors this signal to check for a
sudden change in single or multiple wheel decelerations. If the deceleration of one or more wheels is not within a predetermined amount, the CAB
takes control for antilock action through the HCU. Each WSS has a magnetic inductive pick up coil (WSS) that is mounted to a fixed component.
There is an air gap between the tone wheel and the speed sensor assembly. Diagnostically, the coils of the Wheel Speed Sensors have the same amount
of resistance. When measured across the CAB harness connector terminals, the resistance should be between 1100 1800 ohms. Refer to service
manual for WSS replacement and air gap specifications.
Correct ABS operation is dependent on Tone Wheel speed signal from the WSS. The vehicle wheels and tires should all be the same size and type to
get accurate signals. In addition, all tires should be at recommended tire pressures.
SELF TESTS
The system software includes several self tests that are performed every time the ignition is turned on and the vehicle is driven. Some of the self tests
occur immediately, while others occur under normal driving conditions while not in antilock operation. The CAB checks continuously for a missing or
erratic WSS signals/circuits, tone wheels, solenoids, pump motor or solenoid relay by performing several tests such as: dynamic, static, ohmic, voltage
drop, and timed response. If any component exhibits a fault during testing, the CAB will request to illuminate the ABS and TCS warning indicators.
As an additional check of the ESP system, a road test procedure is available on the DRBIII. This test should be carried out when any ESP component
is replaced in order to ensure proper function. Since the wheel speed sensors are required inputs to the ESP, this test should also be performed if the
wheel speed sensors are replaced.
First, the brakes are applied with the vehicle stationary. Then, the vehicle is driven at approximately 6 MPH. The driver has to make left and right
turns, with a minimum 90 degree steering turning angle. If the indicator lamp goes out, everything is in order. If the lamp remains illuminated, the
DRBIII will display the fault codes that are causing the test to fail. The road test function is set in the ESP control module, and can only be deactivated
once there are no more fault codes detected.
The Steering Angle Sensor must be initialized. A procedure is carried out using the DRBIII to ensure that the module detects the exact position of the
sensor. The sensor must be calibrated any time wheel alignment is changed, the steering column is removed and re installed, or the sensor is replaced.
