2021-2024 Ford Bronco ABS Light On: Common Causes and Fixes

By Core Brake Parts Tech Team — Circleville, OH warehouse

An amber ABS light on a 2021-2024 Ford Bronco means the ABS module has found a fault and switched anti-lock braking off. Ford's owner's manual says the Bronco keeps normal braking without the ABS function, so you can still stop. The usual causes are a wheel speed sensor, its wiring, or the rear tone ring, and a scan for C-codes will narrow it down.

What the ABS Light Means on a Bronco

The Bronco's dash has two brake warnings, and they mean different things. The amber ABS lamp comes on briefly when you switch the ignition on, as a bulb check. Ford says that if it lights up while you drive, the anti-lock system has a malfunction. If it does not light at key-on, or it flashes at any point, Ford says to have the system checked.

The red brake system warning lamp is the more serious one. It comes on when the parking brake is applied with the ignition on. If it stays lit while you drive and the parking brake is released, Ford says the brake fluid is low or the brake system needs service. You may also see a "Brake Fluid Level Low" or "Check Brake System" message. Ford's advice for "Check Brake System" is to have it checked before you keep driving.

If the ABS and red brake lamps are both on, don't treat it as a sensor problem. Check the fluid level first and get the vehicle inspected before you drive it normally.

How the Bronco Knows Something Is Wrong

Each wheel has a speed sensor aimed at a toothed or magnetic target ring that turns with the hub or axle. Bosch, which makes these sensors for many carmakers, explains that modern active sensors use a Hall-effect chip. The chip reads the changing magnetic field from the passing encoder ring and turns it into digital pulses that track wheel speed, down to a near stop. Both ABS and electronic stability control depend on that signal.

The ABS module constantly compares all four wheel speeds. If one signal drops out, goes erratic or doesn't make sense, the module stores a C-code, turns on the ABS lamp and disables anti-lock braking. Stability control uses the same wheel speed data, so the traction or stability control light often comes on too. On a Bronco, trail features can also show faults, because many of them apply the brakes at individual wheels.

Common Causes of an ABS Light on the 2021-2024 Bronco

Rear tone ring damage or movement (early 2021 builds)

Ford issued Special Service Message SSM 50296 for some 2021 Bronco and Ranger vehicles built from June 15, 2021 through August 15, 2021. On those trucks, the ABS lamp with codes C003A, C0036, C0037 and/or C0039 may be caused by damage to the rear axle's ABS tone ring or the ring moving out of position. Ford tells technicians to remove the ABS sensor and inspect the ring. If it has moved or been damaged, the repair is an axle shaft replacement under the workshop manual procedure. If the ring looks fine, they go on to normal ABS diagnosis. That is why a new sensor alone may not fix the light on an affected truck.

Mud, rust and metallic debris on the sensor

Brake and Front End, a technical magazine for the repair trade, notes that metallic particles can stick to the magnetic tip of a wheel speed sensor and interfere with the signal. That causes false ABS codes. An off-road truck like the Bronco collects plenty of mud, grit and rust scale around its hubs. Pulling the sensor, cleaning the tip and cleaning the mounting bore is a reasonable first check before you buy parts.

Sensor air gap problems

The same source says the gap between the sensor tip and the ring is critical. Too wide a gap gives a weak or erratic signal, and too tight a gap can damage the sensor. Anything that changes the gap can set a code, such as a sensor not fully seated after brake work, rust buildup under the sensor, or a worn wheel bearing that lets the hub move.

Wiring and connector damage

Sensor leads on a Bronco run near the suspension and are exposed to rocks, brush and water. Brake and Front End points out that loose or corroded connectors and damaged wiring produce the same weak signals as a failing sensor. Before replacing the sensor, test continuity from the sensor to the harness so you know which part has failed.

Tire size and modifications

Many Bronco owners change tires and wheels. In the stability control section, Ford warns that changes to the braking system, suspension, steering, tire construction and wheel or tire size can affect how the stability control system performs. Elsewhere the manual warns that dissimilar tire sizes affect four-wheel-drive shifting. If the light came on right after a lift, a new tire size or a mismatched spare, include that in the diagnosis.

Low fluid or other brake faults

Worn pads let the fluid level drop in the reservoir as the caliper pistons move out. Low fluid, or a leak, turns on the red brake lamp, and some brake faults also set ABS codes. Check the reservoir level against the MIN and MAX marks with the vehicle parked on level ground. Ford says the reservoir cap should stay in place and fully tight unless you are adding fluid.

How to Diagnose It Step by Step

1. Read the codes. A generic engine-code reader often cannot see ABS codes. You need a scan tool that reads the ABS module. The code points to a circuit or a wheel position.
2. Check the fluid. Confirm the level is between MIN and MAX and look for wet spots at each wheel and along the lines.
3. Look at the flagged wheel. Look for torn or pinched sensor wiring, a sensor that has backed out, and mud or rust packed around it.
4. Remove, clean and inspect. Clean the sensor tip and its bore. On a rear-wheel code, look at the tone ring through the sensor hole for cracks, missing teeth or signs it has moved. That is the SSM 50296 check.
5. Test the circuit. Check the wiring and connectors before you condemn the sensor. A scan tool that shows live wheel speed data will show which wheel drops out.
6. Check bearing play. A loose hub can open the air gap. If you find play, repair the bearing before you replace the sensor.
7. Clear and road test. After the repair, clear the codes and drive to confirm the light stays off.

Fixes, Parts and What to Replace Together

The fix follows what the diagnosis finds. A dirty sensor may only need cleaning. A failed sensor or damaged lead gets replaced. A damaged or displaced rear tone ring on an early 2021 truck is a dealer-level axle shaft repair under Ford's procedure. A worn front hub needs a hub assembly, because the sensor reads from it.

ABS faults often show up during or after a brake job, because the sensors sit right next to the calipers and rotors. When you do front or rear brakes on a Bronco, route the sensor wiring back into its original clips and keep it clear of the rotor and caliper. Don't pry on the sensor body. The rear brakes also carry the electric parking brake, and Ford's manual has its own warning lamp and troubleshooting section for that system.

If the pads are near the end, replace them and check the rotors at the same visit. Worn pads lower the fluid level and can trigger brake warnings of their own. Browse brake pads and brake rotors, or brake hardware kits so the new pads slide freely in the brackets. If the diagnosis finds a leaking caliper or damaged hose, see our brake calipers and brake hoses. When you top off or flush, Ford recommends DOT 4 Low Viscosity (LV) High Performance brake fluid meeting WSS-M6C65-A2 or ISO 4925 Class 6. Use fluid only from a sealed container.

How Hard Is the Repair?

Reading codes, checking fluid and cleaning a sensor are driveway jobs if you have a scan tool that reads ABS. Replacing a wheel speed sensor is usually one bolt and a connector. A rusted-in sensor can break on removal, though, so soak it with penetrant and work it out slowly. Hub bearing replacement takes more tools and time. Rear axle shaft work for a damaged tone ring, and any ABS module or electronic brake booster diagnosis, are best left to a shop with Ford's diagnostic software. Before any warranty or dealer visit, ask whether open recalls or service messages apply to your VIN.

Frequently Asked Questions

Is it safe to drive a Ford Bronco with the ABS light on?

Ford's manual says the vehicle keeps normal braking without the anti-lock function, so it will stop. The wheels can lock in a panic stop or on slick surfaces, though, and stability control may be limited too. Drive carefully and get it diagnosed soon. If the red brake lamp is also on, have the brakes checked before normal driving.

Why did my ABS light come on after a brake job?

The most common reasons are a sensor wire that got stretched, pinched or left unclipped, a sensor knocked out of position, or a connector left unplugged. Recheck the sensor at every wheel you worked on before buying parts.

Does SSM 50296 apply to my 2022-2024 Bronco?

No. Ford's SSM 50296 lists 2021 Bronco and Ranger vehicles built from June 15, 2021 through August 15, 2021. Later trucks with the same codes follow normal ABS diagnosis. The service message is also not a recall, so a dealer can tell you how it would be handled on your VIN.

Can bigger tires cause an ABS or stability control light?

Ford warns that changing wheel and tire size can affect how the stability control system performs. If a warning appeared right after a tire change, include the new size in the diagnosis and ask the dealer or a shop whether the vehicle needs to be reprogrammed for it.

Will disconnecting the battery clear the ABS light?

Some ABS faults clear on their own once the signal returns, but a hard fault comes back as soon as the module sees the problem again. Fix the cause, then clear the code with a scan tool that reads the ABS module.

Sources

1. Ford - 2021 Bronco Owner's Manual - ABS lamp, red brake lamp, electric park brake lamp and messages, fluid check, DOT 4 LV fluid spec, tire size and modification warnings
2. NHTSA - Ford SSM 50296, 2021 Ranger/Bronco Illuminated ABS Warning Lamp - affected build dates, codes C003A, C0036, C0037, C0039, rear tone ring inspection and repair
3. Bosch Mobility - Wheel-Speed Sensor - how Hall-effect wheel speed sensors and encoder rings work; use by ABS and stability control
4. Brake and Front End - Tech Tip: Wheel Speed Sensor Service - debris on sensor tips, air gap, wiring and connector faults, tone ring damage