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1) This is a typical antilock braking system. (1) Master Cylinder and distribution block, (2) ABS warning light, which illuminates at engine start and during a malfunction only, (3) wheel sensors, (4 and 5) wheel sensor as it relates to the reluctor (trigger wheel), (6) electronic control unit, (7) electronic controller and hydraulic control unit.

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2) An antilock braking system is conventional in scope. This is the power brake booster and master cylinder, which are located ahead of the ABS system. You apply brakes and braking hydraulic pressure goes to all four brakes via the ABS controller. The connector shown here is not related to the ABS.

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3) If you’re searching for the ABS good luck because most are well hidden. This is a 2011 Ford Expedition/F150 engine compartment where ABS is hidden down below at the frame rail. The air intake system must be removed for access.

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4) With everything out of the way, you can see the ABS electronics and hydraulic all contained in one place as an integral unit. Not all systems are like this. Some have a separate electronic controller and relays.

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5) The electrohydraulic controller has six brake lines — two from the master cylinder going in for front and rear brakes, and four out to four brakes. The hydraulic side of the control unit has an electric motor, which runs (pulses) the antilock valving.

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6) This is an exploded view of a Ford ABS control unit. (1, 2, and 3) are the electronic control module and fasteners, (4) is the brake line manifold, (5 and 6) are the insulated mounts and fasteners, (7) is the brake hydraulic control unit and motor, (8 and 9) are fasteners and mounts. Because the ABS unit can get noisy, rubber mounts are paramount to isolate noise on the rare occasion they are needed.

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7) Not all brake sensors are easy to find let alone see. Because they require protection, they tend to be hidden in the brake assembly. Just follow the wire from the chassis plug to the sensor.

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8) This brake sensor is hidden beneath the rubber boot, which keeps moisture and road debris out.

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9) Here’s a front disc brake spindle and brake sensor. Notice the accumulated debris and metal shavings on this front disc brake sensor. It should be cleaned with brake cleaner for proper operation.

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10) The brake sensor interacts with this reluctor or trigger wheel, which makes and breaks the signal with steady precision. When this reluctor suddenly slows or stops, the ABS goes to work pulsing the brakes until wheel rotation returns to normal.

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11) Here’s a Ford 8.8-inch rear axle with the brake sensor incorporated into the differential housing. The sensor is located in the housing as shown. The reluctor wheel is located on the ring gear inside. (1) is the sensor plug, (2) is the sensor retaining bolt, (3) is the brake or speed sensor, (4) is the o-ring seal and sensor opening, (5) is the axle housing.

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12) This is an up-close look at the rear axle brake/speed sensor and related parts. (1) is the sensor port, (2) is the sensor, (3) is the sensor sealing o-ring, (4) is again the speed sensor.

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13) Inside the Ford rear axle is a reluctor (trigger) wheel with teeth that pass the sensor as you roll down the road. Ford wants .005 to .045-inch clearance between sensor and reluctor.

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14) When you are troubleshooting your ABS, begin at wiring and sensors. Follow sensor wiring harnesses and check for breaks and shorts to ground.

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15) Dirty brake fluid is never acceptable and indicates contamination. Flush your brake hydraulic system every two years when you flush the cooling system.