The ABS/TC system is rather complex. The codes (one is likely stored if it'* recent) can only be pulled by the dealer. Any of the diagnostics refer to using at Tech II scanner. If you want to check all of the connections in the system, I've posted the description and operation below. The easier way is to have the dealer scan it, and it will point right to where the problem is - perhaps an intermittent wheel speed sensor?
Depending on your options, you may not have all of the following on your car.
BPMV and EBCM
Brake Pressure Modulator Valve (BPMV)
The brake pressure modulator valve (BPMV) is mounted on the left front side of the engine compartment. The BPMV provides brake fluid modulation for each of the individual wheel circuits as required during DRP/ABS/TCS/VSES. During DRP/ABS, the BPMV can maintain or reduce brake fluid pressure independent of the pressure generated in the master cylinder. The BPMV does not provide more pressure than is applied by the master cylinder during braking.
With the exception of the EBCM, the BPMV is an integral, non-serviceable component. The BPMV should never be disassembled.
The BPMV uses a 4 circuit configuration with a diagonal split. Individual circuits are provided for the left front and right rear wheels, and right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.
The BPMV consists of several other components:
* The pump motor
* The ABS valves
* The TCS master cylinder isolation valves (if equipped)
* The TCS prime valves (if equipped)
The BPMV contains a motor driven recirculation pump. The pump serves 2 purposes:
* Transfers fluid from the brake calipers to the master cylinder during DRP/ABS reduce pressure events
* Transfers fluid from the master cylinder reservoir to the front brake calipers during TCS/VSES. The pump and motor are located within the BPMV and are not serviced separately.
BPMV Bracket Bolts and Isolators
The 2 BPMV bracket bolts are used to attach the BPMV to the BPMV bracket. Beneath each BPMV bracket bolt is a rubber isolator. There is also a rubber isolator on the bottom of the BPMV. The isolators reduce the vibration, which is associated with vehicle operation, on the BPMV and EBCM.
The BPMV bracket bolts and isolators are included with a new BPMV or EBCM/BPMV assembly, but may be serviced separately.
The ABS valves decrease or maintain brake fluid pressure at the individual wheel circuits. There are 4 inlet and 4 outlet solenoid valves. The solenoid valves maintain, increase, or decrease brake fluid pressure to the individual wheel circuits. The EBCM commands the valves to their correct position during DRP/ABS/TCS/VSES. During DRP/ABS, the pressure in each hydraulic circuit can be held or released by activating the appropriate valves. The normal state of the inlet valves is open, while the normal state of the outlet valves is closed. This allows direct master cylinder pressure to the brakes during normal braking. The ABS valves are located within the BPMV and are not serviced separately.
TCS Master Cylinder Isolation Valves
With TCS (NW9), there are 2 TCS master cylinder isolation valves within the BPMV. These valves isolate the master cylinder so the pump motor can build brake fluid pressure for the front brakes during a traction event. Unlike the ABS valve solenoids, the isolation valves do not modulate. The isolation valves are normally open and then close during TCS/VSES.
TCS Prime Valves
With TCS (NW9), there are 2 TCS prime valves within the BPMV. These valves allow the pump to draw fluid from the master cylinder reservoir, through the compensating ports in the master cylinder bore. The prime valves do not modulate. The prime valves are closed during normal operation and open during TCS/VSES.
Electronic Brake Control Module (EBCM)
The EBCM performs the following functions:
* Monitor the wheel speed sensor (WSS) inputs
* Determine wheel slip tendencies
* Control the brake system while in antilock mode or a traction event
* Monitor the system for proper operation The EBCM continuously checks the speed of each wheel in order to determine if any wheel is beginning to slip. If a wheel slip tendency is detected, the EBCM commands appropriate valve positions in order to modulate brake fluid pressure in some or all of the hydraulic circuits. This prevents wheel slip and provides optimum braking. The EBCM continues to control pressure in individual hydraulic circuits until a slipping tendency is no longer present. If the EBCM detects an error, the EBCM can perform the following actions:
* Disable the dynamic rear proportioning (DRP)
* Disable the antilock braking system (ABS)
* Disable the traction control system (TCS)
* Disable the vehicle stability enhancement system (VSES)
* Turn ON the ANTILOCK, the TRAC OFF, and/or the LOW TRAC indicators in the instrument cluster
* Turn ON the SERVICE STABILITY SYSTEM message on the DIC The EBCM transmits torque request signals to and receives delivered torque signals from the PCM.
System Enable Relay
The system enable relay provides power to the pump motor during DRP/ABS/TCS/VSES and power to the solenoid valves in the BPMV. This relay is an integral part of the EBCM and cannot be serviced separately.
The electronic brake control module (EBCM) defines a drive cycle as the completion of the EBCM initialization sequence. The EBCM will perform the initialization sequence one time in each ignition cycle. Refer to Initialization Sequence.
Traction Control Switch
With TCS (NW9), the traction control switch is a momentary ON switch that allows the driver to shut off the TCS for personal or diagnostic reasons. Turning the system off places the TCS in passive mode while retaining DRP/ABS/VSES functions. When the TCS system is turned OFF, the TRAC OFF indicator is turned ON. The switch is located on the center console, near the gear shifter.
The stoplamp switch is an input to the EBCM. The EBCM uses the stoplamp switch to tell when the brake pedal is being applied so that traction control can be disabled if necessary.
Wheel Speed Sensors (WSS)
A wheel speed sensor (WSS) is present at each wheel. The sensors transmit wheel speed information to the EBCM by means of a small AC voltage. This voltage is generated by magnetic induction caused by passing the toothed sensor ring (part of the integral hub/bearing assembly) past the stationary sensor. The signal is transmitted to the EBCM through shielded wiring in order to help reduce electro-magnetic interference that can cause false or noisy WSS inputs to the EBCM.
The front wheel speed sensors are located in the hub/bearing assembly and are non-adjustable. Sensor gap is set at the time of assembly.
The rear wheel speed sensors are mounted in the bearing assembly and are non-adjustable. Sensor gap is set at the time of assembly.
Pin E of the EBCM harness connector is a plastic vent tube that vents the cavity between the EBCM and the BPMV to the underhood fuse block.
The lateral accelerometer is a self contained unit which uses a reference voltage of 5 volts. The sensor'* operating range is ±1.5 g, resulting in an output range of 0.25-4.75 volts. Zero lateral acceleration results in an output signal of 2.5 volts. The lateral accelerometer is located under the rear driver'* side seat cushion, attached to the number 4 bar.
Yaw Rate Sensor
The yaw rate sensor is a self contained unit which uses a reference voltage of 5 volts. The sensor'* range is ±75 degrees/second, resulting in a signal proportional output of 0.25-4.75 volts . Zero yaw rate is 2.5 volts . The yaw rate sensor is located behind the rear compartment trim, under the rear package shelf.
Steering Wheel Position Sensor (SWPS)
The steering wheel position sensor (SWPS) sends dual analog signals to the EBCM. The EBCM determines steering wheel position and rotation from these signals.
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