Antilock Brakes / Traction Control Systems: Description and Operation

Anti-Lock Control-Anti-Wheel spin Control
The Crown Victoria and Grand Marquis are equipped with a 4-wheel Anti-Lock Brake System (ABS) with optional Traction Control (TC).

The anti-lock brake system:
^ prevents wheel lock-up by automatically modulating brake pressure during an emergency stop.
^ allows the driver to maintain steering control and stop the vehicle in the shortest possible distance under most conditions.

The traction control system, if equipped, controls Wheel spin by modulating engine torque and applying then releasing the appropriate rear brake to restore traction when driving on slippery or loose surfaces.

Brake Fluid

WARNING: of any other than approved DOT 3 brake fluid win cause permanent damage to brake components and will render the brakes inoperative.

WARNING: Brake fluid contains polyglycol ethers and polyglycols. Avoid contact with eyes. Wash hands thoroughly after handling. If brake fluid contacts eyes, flush eyes with running water for 15 minutes. Get medical attention if irritation persists. If taken internally, drink water and induce vomiting. Get medical attention immediately.

CAUTION: Brake fluid is harmful to painted or plastic surfaces. If brake fluid is spilled onto a painted or plastic surface, immediately wash it with water.

Use clean, fresh Ford High Performance DOT 3 Motor Vehicle Brake Fluid C6AZ-19542-AB or equivalent meeting Ford specification ESA-M6C25-A.
^ Do not reuse brake fluid drained or bled from the system.
^ Do not use brake fluid that has been stored in an open container.
^ Do not use contaminated brake fluid.

Electronic Brake Distribution (EBD)
The Electronic Brake Distribution (EBD) controls rear brake pressure and acts as an electronic proportioning valve. It is controlled by the anti-lock brake control module. When EBD is disabled, the brake warning indicator will illuminate.

Anti-Lock Brake System
The Anti-Lock Brake System (ABS) operates as follows:
^ When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the Hydraulic Control Unit (HCU) inlet ports. This pressure is transmitted through the normally open solenoid valves contained inside the HCU, then through the outlet ports of the HCU to each wheel.
^ The primary (rear) circuit of the brake master cylinder feeds the right front and left front brakes on vehicles with ABS.
^ The secondary (front) circuit of the brake master cylinder feeds the left rear and right rear brakes on vehicles with ABS and TC.
^ The primary (rear) circuit of the brake master cylinder feeds the left rear and the right rear brake on vehicles without TC.
^ The secondary (front) circuit of the brake master cylinder feeds the left front and the right front brake on vehicles without TC.
^ If the anti-lock brake control module senses a wheel is about to lock, based on wheel speed sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.
^ The anti-lock brake control module then looks at the anti-lock brake sensor signal from the affected wheel again.
^ If that wheel is still decelerating, it opens the normally closed solenoid valve for that circuit to reduce hydraulic pressure.
^ Once the affected wheel comes back up to speed, the anti-lock brake control module returns the solenoid valves to their normal condition allowing fluid flow to the affected brake and the ABS pump motor deactivates.
^ The anti-lock brake control module monitors the electromechanical components of the system.
^ Malfunction of the anti-lock brake system will cause the anti-lock brake control module to shut off or inhibit the system. However, normal power-assisted braking remains.
^ Malfunctions are indicated by the yellow ABS warning indicator on the Hybrid Electronic Cluster (HEC).
^ The 4-wheel anti-lock brake system is self-monitoring. When the ignition switch is fumed to the RUN position, the anti-lock brake control module will perform a preliminary self-check on the anti-lock electrical system indicated by a three second illumination of the yellow ABS warning indicator in the HEC.
^ During vehicle operation, including normal and anti-lock braking, the anti-lock brake control module monitors all electrical anti-lock functions and some hydraulic operations.
^ Each time the vehicle is driven, as soon as vehicle speed reaches approximately 12 km/h (7.5 mph), the anti-lock brake control module turns on the pump motor and valves for approximately one-half second. At this time, a mechanical noise may be heard. This is a normal function of the self-check by the anti-lock brake control module.
^ Most malfunctions of the anti-lock brake system and traction control system, if equipped, will cause the yellow ABS warning indicator to illuminate.

Traction Control
The traction control system, consists of or uses the following components:
^ Anti-lock brake control module
^ Powertrain Control Module (PCM)
^ Front wheel speed sensors
^ Rear wheel speed sensors
^ Traction control switch

The traction control system:
^ Is operational when the ignition switch is in the RUN position.
^ Can be disabled by the driver pressing the traction control switch. The traction control system will reset when the ignition switch is cycled or when the traction control switch is pressed again.
^ Is controlled by the anti-lock brake control module.
^ Applies and releases the appropriate rear brake to reduce Wheel spin and aid traction if one or both rear wheels lose traction and begin to spin during acceleration.
^ Interacts with the PCM to reduce engine torque if one or both rear wheels lose traction and begin to spin during acceleration.
^ If a hydraulic brake system malfunction occurs, engine torque modulation remains enabled.
^ Automatically stops traction control system cycling if the brakes are manually applied during traction control system operation. Engine torque modulation remains enabled.
^ When the traction control system is disabled either by the driver or by the anti-lock brake control module, rear brake modulation is disabled.
^ With the traction control system on, brake modulation to the spinning wheel is achieved by the anti-lock brake control module closing the isolation valves to the non-affected wheels and running the pump motor that provides hydraulic pressure for brake modulation to the spinning wheel.
^ Engine torque modulation is achieved by the anti-lock brake control module interacting with the PCM to regulate fuel, spark and cylinder.

Hydraulic Control Unit
The hydraulic control unit is located in the engine compartment on a bracket attached to the frame rail. The brake pressure control valve block and pump motor are installed as an assembly. It consists of the following components:
^ brake pressure control valve block
^ pump motor

Operation of the hydraulic control unit is as follows:
^ During normal braking, fluid passes through four normally open inlet valves, one to each wheel.
^ If the anti-lock brake control module senses a wheel is about to lock, it pulses the appropriate inlet valve which closes that valve. This prevents any more fluid from entering the affected brake.
^ The anti-lock brake control module then looks at that wheel again. If it is still decelerating, it opens the normally closed outlet valve which decreases the pressure trapped in the line.

Anti-Lock Brake Control Module
The anti-lock brake control module is mounted to the hydraulic control unit.
It is an on-board diagnostic, replaceable unit consisting of two microprocessors and the necessary circuitry for their operation. The anti-lock brake control module monitors system operation during normal driving as well as during anti-lock braking and traction control cycling, if equipped.
Anti-lock brake control module operation is as follows:
^ Under normal driving conditions, the microprocessor produces short test pulses to the solenoid valves that check the electrical system without any mechanical reaction.
^ Impending wheel lock conditions trigger signals from the anti-lock brake control module that open and close the appropriate solenoid valves. This results in moderate pulsations in the brake pedal.
^ During normal braking, the brake pedal feel will be identical to a standard brake system.
^ Most faults which occur to the anti-lock brake system and the traction control will be stored as a Diagnostic Trouble Code (DTC) in the keep-alive memory of the anti-lock brake control module. The DTC'S can be retrieved by following the on-board diagnostic procedures.

Warning Lamp Indicators
The anti-lock brake system uses one yellow ABS warning indicator to alert the driver of malfunctions in the system.
The yellow ABS warning indicator will illuminate for numerous reasons. It warns the driver that the ABS and traction control have been turned off due to a symptom that exists in the system. Normal power assisted braking remains but the wheels can lock during a panic stop while the yellow ABS warning indicator is illuminated.
The Electronic Brake Distribution (EBD), system will only function if the anti-lock brake system is operational. If there is an ABS fault, the EBD system is disabled and the brake warning indicator and the ABS warning indicator will illuminate.
The traction control indicator will flash when TC activates while the vehicle is being driven. The traction control indicator will remain illuminated if the driver turns TC off or if there is a fault in the TC system.

Anti-Lock Brake Sensor
The anti-lock brake system uses four variable-reluctance sensors to determine vehicle speed. The anti-lock brake sensors operate on magnetic induction principles. As the teeth on the anti-lock brake sensor indicator rotate past the stationary anti-lock brake sensor, a signal proportional to vehicle speed is generated and sent to the anti-lock brake control module.

Front
The front anti-lock brake sensors are non-adjustable. The front anti-lock brake sensors and the front anti-lock brake sensor indicators are replaced separately.
The front anti-lock brake sensors are attached to the front wheel spindles. Front anti-lock brake sensor indicators are pressed onto the wheel hubs.

Rear
The rear anti-lock brake sensors are attached to the rear axle housings and the rear anti-lock brake sensor indicators are pressed onto the axle. Both are replaced separately.