# 4-Wheel Anti-lock Brake System (ABS)

## General Information

The 4-Wheel Anti-lock Brake System (ABS) is an electronically operated, all wheel brake control system. Major components include the power brake booster, master cylinder, the wheel speed sensors, and the Hydraulic Control Unit (HCU) which contains the control module, a relay, and the pressure control valves.

The system is designed to retard wheel lockup during periods of high wheel slip when braking. Retarding wheel lockup is accomplished by modulating fluid pressure to the wheel brake units. When the control module detects a variation in voltage across the wheel speed sensors, the ABS is activated. The control module opens and closes various valves located inside the HCU. These valves, called dump and isolation valves, modulate the hydraulic pressure to the wheels by applying and venting the pressure to the brake fluid circuits.

## Diagnosis and Testing

The ABS module performs system tests and self-tests during startup and normal operation. The valves, wheel sensors and fluid level circuits are monitored for proper operation. If a fault is found, the ABS will be deactivated and the amber ANTI LOCK light will be lit until the ignition is turned OFF. When the light is lit, the Diagnostic Trouble Code (DTC) may be obtained. Under normal operation, the light will stay on for about 2 seconds while the ignition switch is in the ON position and will go out shortly after.

The Diagnostic Trouble Codes (DTC) are an alphanumeric code and a scan tool, such as Rotunda NGS Tester 007-00500 or its equivalent, is required to retrieve the codes. Refer to the manufacturer's instructions for operating the tool and retrieving the codes.

The data link connector (DLC) for the ABS is the OBDII connector located under the driver's side of the instrument panel, underneath the steering column.

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## Speed Sensors

### REMOVAL & INSTALLATION

#### Front

Wheel speed sensor mounting—4 X 2 models

Wheel speed sensor mounting—4 X 4 models

1. Raise and safely support the vehicle securely on jackstands.
2. Remove the wheel and tire assembly.
3. On 4 X 4 models except for F-250SD, F-350 and F-Super Duty models, remove the disc brake rotor shield.
4. On 4 X 4 F-250SD, F-350 and F-Super Duty models, remove the disc brake rotor.
5. Detach the front anti-lock brake sensor electrical connector.
6. Separate the sensor cable from the brake hose clips.
7. Remove the front anti-lock brake sensor bolt and the front anti-lock brake sensor.
8. The installation is the reverse of the removal.

#### Rear

Detach the connector on the speed sensor

Remove the sensor hold-down bolt and ...

Remove the sensor

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The sensor is located on the rear axle housing.

1. Raise and safely support the vehicle securely on jackstands.
2. Carefully clean the axle surface to keep dirt from entering the housing.
3. Detach the connector on the speed sensor.
4. Remove the sensor hold-down bolt.
5. Remove the sensor.
6. If a new sensor is being installed, lubricate the O-ring with clean engine oil. Carefully push the sensor into the housing aligning the mounting flange hole with the threaded hole in the housing. Tighten the hold-down bolt to 30 ft. lbs. (41 Nm)—If the old sensor is being installed, clean it thoroughly and install a new O-ring coated with clean engine oil.
7. Attach the connector on the speed sensor.
8. Lower the vehicle.

## Tone (Exciter) Ring

### REMOVAL & INSTALLATION

#### Front

##### 4 X 2 MODELS

1. Raise and support the front end on jackstands.
2. Remove the wheels.
3. Remove the caliper, rotor and hub.
4. Using a 3-jawed puller, remove the ring from the hub. The ring cannot be reused; it must be replaced.

To install:

5. Support the hub in a press so that the lug studs do not rest on the work surface.
6. Position the new sensor ring on the hub. Using a cylindrical adapter 98mm IDx106mm OD, press the ring into place. The ring must be fully seated!
7. The remainder of installation is the reverse of removal.

Front wheel sensor ring removal and installation—4-wheel ABS

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##### 4 X 4 MODELS

The exciter ring is integral to the hub assembly. Refer to Section 7.

#### Rear

The exciter ring is located in the differential case inside the axle housing on the rear gear. The rear differential must be disassembled to replace the ring. Refer to Section 7.

## Hydraulic Control Unit

### REMOVAL & INSTALLATION

Disconnect and plug the hydraulic brake lines

Remove the HCU retaining bolts and remove the HCU

1. Disconnect the negative battery cable.
2. On Super Duty models, remove the air cleaner assembly.
3. On Super Duty models, remove the EVAP canister.
4. Detach the anti-lock brake control module electrical connectors.

CAUTION
Brake fluid contains polyglycol ethers and polyglycols. Avoid contact with the eyes and wash your hands thoroughly after handling brake fluid. If you do get brake fluid in your eyes, flush your eyes with clean, running water for 15 minutes. If eye irritation persists, or if you have taken brake fluid internally, IMMEDIATELY seek medical assistance.

5. Disconnect and plug the hydraulic brake lines.
6. Remove the HCU retaining bolts and remove the HCU.
7. If necessary, remove the HCU bracket.

To install:

8. If removed, install the HCU bracket.
9. Position the HCU.
10. Install and tighten the retaining bolts.
11. Connect the hydraulic brake lines.
12. Connect the anti-lock brake control module electrical connectors.
13. On Super Duty models, install the EVAP canister.
14. On Super Duty models, install the air cleaner assembly.
15. Connect the negative battery cable.
16. Bleed the 4-wheel ABS.

## Control Module

### REMOVAL & INSTALLATION

Remove the module retaining screws and remove the anti-lock brake control module

WARNING
Electronic modules are sensitive to static electrical charges. If exposed to these charges, damage may result.

1. Disconnect the negative battery cable.
2. Detach the anti-lock brake control module electrical connectors.
3. Remove the module retaining screws and remove the anti-lock brake control module.
4. The installation is the reverse of the removal.

## Bleeding the ABS System

CAUTION
Brake fluid contains polyglycol ethers and polyglycols. Avoid contact with the eyes and wash your hands thoroughly after handling brake fluid. If you do get brake fluid in your eyes, flush your eyes with clean, running water for 15 minutes. If eye irritation persists, or if you have taken brake fluid internally, IMMEDIATELY seek medical assistance.

If equipped with the 4 wheel anti-lock brake system and the Hydraulic Control Unit (HCU) has been replaced or is suspected of containing trapped air, bleed the brake system using the procedure below. Conventional brake system bleeding cannot remove the air trapped in the lower portion of the HCU.

If a spongy brake pedal is present and air in the hydraulic control unit is suspected, use the following procedure:

1. Bleed the brake system as outlined in the conventional bleeding procedure.
2. Connect a New Generation Star (NGS) tester or equivalent scan tool, to the serial data link connector below the instrument panel as though retrieving codes.
3. Make sure the ignition switch is in the RUN position.
4. Follow the instructions on the NGS screen. Verify correct vehicle and model year go to the "Diagnostic Data Link" menu item, choose ABS Module, choose "Function Tests", and choose "Service Bleed".

WARNING
Do not allow the brake master cylinder to run dry of brake fluid during the brake bleeding procedure. Only use new DOT 3 or equivalent brake fluid from a closed container.

5. Bleed the right-front wheel as follows:
   1. Open the caliper bleed screw and pump the brake pedal for 3 seconds. Repeat the procedure again.
   2. When the fluid runs clear, begin the program and continue to pump the brake pedal.
   3. Continue bleeding for approximately 1 to 2 minutes after the program ends and then tighten the bleed screw.
6. Repeat the bleeding procedure to the left-front, left-rear and finally the right-rear wheel.
7. Remove the pressure bleeding device and adjust the brake fluid level.
8. Road test the vehicle and check for proper brake system operation.