How do I know if my ABS relay is bad?

Yes. Common signs include the ABS warning light staying on, the brake/ABS pump failing to run when braking, or an abnormal relay click or no click at all. You can verify with a combination of visual checks, relay swapping, electrical testing, and diagnostic codes from an OBD scanner.

What the ABS relay does

The ABS relay (often called the ABS pump relay) supplies power to the hydraulic pump and the valves that modulate brake pressure during an ABS event. In many vehicles, it sits in the engine bay fuse/relay box or near the ABS module. If the relay sticks, overheats, or fails, the pump may not run when the system activates, compromising anti-lock braking control. Understanding its role helps distinguish relay problems from sensor or module faults.

Common symptoms of a failing ABS relay

Signs that the ABS relay could be failing are best understood as a cluster of symptoms rather than a single telltale signal. The following indicators often appear together when the relay is at fault, though other ABS components can mimic them.

• The ABS warning light is illuminated on the instrument cluster, even if wheel-speed sensors show no obvious issues.


• The ABS pump does not run when you start the car or apply the brakes during a situation that would normally trigger ABS.


• You hear an unusual noise, click, or buzzing from the fuse/relay area, or there is no audible click when the system should energize the pump.


• A fuse for the ABS circuit is repeatedly blowing, or the relay tends to overheat and has a burnt smell or crust on the terminals.


• Intermittent ABS operation or abrupt, inconsistent braking feel that coincides with relay cycling.

These symptoms suggest the relay could be at fault, but they can also be caused by wiring problems, a faulty pump, or sensor issues. A systematic check is necessary to confirm.

How to test the ABS relay

To systematically determine whether the ABS relay is contributing to the problem, follow these steps. Always observe safety precautions when working around the braking system and electrical components.

1. Locate the ABS pump relay in your vehicle’s fuse/relay box. Check the owner’s manual or a labeling diagram on the box lid to confirm the exact position and coil rating.


2. With the ignition off, disconnect the vehicle battery negative terminal to prevent shorts and shocks while handling electrical components.


3. Visually inspect the relay and sockets for signs of damage, corrosion, discoloration, or melted plastic. If you see damage, replacement is recommended even if tests pass.


4. Conduct a swap test: if you have an identical relay (same part number and coil rating) in another circuit, swap the two relays temporarily. If the ABS issue follows the relay to the new socket, the relay is likely faulty; if the issue remains in the same circuit, the problem is elsewhere (pump, wiring, or control module).


5. Reconnect the battery and start the car. Listen for the ABS pump to engage when you move the vehicle or apply the brakes under conditions that would normally trigger ABS. If the pump does not run, the relay could be the culprit or there could be a separate power/ground issue.


6. Test the relay coil with a multimeter: remove the relay and measure resistance across the coil terminals (often labeled 85 and 86). Compare the reading to the manufacturer’s specification. A coil resistance that is open (infinite) or near zero typically indicates a bad coil.


7. Check the pump/valve circuit for proper voltage: with the relay energized (coil energized), probe the power feed to the ABS pump terminal. You should see battery voltage (typically ~12V). If there is no voltage, the issue could be the relay contact, wiring, or the control circuit rather than the coil itself.


8. Inspect the ground path for the ABS pump and relay: a poor ground can mimic relay failure. Ensure the ground strap or wire is clean, tight, and free of corrosion.


9. If available, use an OBD-II scanner to check ABS-related codes. Codes pointing to the pump, pump power circuit, or relay-controlled circuits can help confirm whether the relay or another component is at fault.

After these tests, you should have a clearer picture of whether the ABS relay is faulty. If the relay tests show an open/short coil, poor contact, or the swap test moves the problem with the relay, replacement is warranted. If tests show the relay is fine but the pump or wiring has issues, focus on those components.

Other possible causes and how to differentiate

Even with a faulty relay, other parts of the ABS system can create similar symptoms. Wheel speed sensors, wiring harnesses, the ABS control module, or the hydraulic pump and valves themselves can fail. To avoid misdiagnosis, use the relay test as one part of a broader diagnostic approach that includes:

• Inspecting wheel speed sensors for damage, dirt, or misalignment


• Checking for damaged wiring or corroded connectors in the ABS circuit


• Reading ABS diagnostic trouble codes (DTCs) to see whether they point to the pump circuit, sensors, or module


• Testing the ABS pump independently if the vehicle’s service manual provides a safe procedure

When in doubt, consulting a qualified technician familiar with your vehicle’s ABS system is recommended, especially if the car is under warranty or you lack the specialized tools for high-current electrical testing.

Using a scanner to read ABS codes

Modern vehicles often provide ABS-specific codes that help pinpoint a fault within the pump circuit, wheel sensors, or the control module. A generic code reader may not access ABS data in all models; in some cases, you’ll need a dedicated or OEM-level diagnostic tool. If codes reference the pump power circuit or relay, that strengthens the case for testing or replacing the ABS relay.

When to seek professional help

If you’re uncomfortable performing electrical tests, or if the ABS warning light persists after relay checks and basic diagnostics, have a professional diagnose the system. ABS work involves high-current electrical components and critical braking functions, so incorrect handling can compromise safety.

Summary

The ABS relay powers the hydraulic pump and valves that regulate brake pressure during ABS events. Common signs of a bad relay include an illuminated ABS light, no pump operation, unusual relay sounds, or overheating signs. To diagnose, inspect the relay, perform a swap test with an identical unit, measure coil resistance, verify voltage to the pump with the relay energized, and check grounds and wiring. Use an ABS-focused code reader to corroborate findings. If tests indicate a faulty relay, replacement is typically straightforward; otherwise, the issue may lie with the pump, sensors, or the ABS module, which may require professional service.

How to test if an ABS module is bad?

Symptoms of a bad ABS module include the illuminated ABS warning light on the dashboard, spongy or unresponsive brake pedals, brake lock-up, and other warning lights like the check engine or traction control lights. Other signs can include erratic ABS activation, a pulsating brake pedal, or a stuck caliper causing a brake to drag. You should address these issues immediately as they can compromise braking performance and safety. 
Common symptoms 

• Illuminated ABS warning light: This is a common and direct indicator that the system has detected a fault. 
• Spongy or unresponsive brake pedal: The brake pedal may feel soft or require more pressure to achieve the same level of braking. 
• Erratic ABS activation: The ABS may engage unexpectedly and erratically, or the brake pedal may pulsate without a hard brake application. 
• Brake lock-up: The wheels may lock up during braking because the anti-lock function is not working correctly. 
• Other warning lights: The check engine light or traction control light may also illuminate, sometimes along with the ABS light. 
• Brake drag: A stuck caliper or other brake component, potentially caused by the ABS module's fault, can cause a brake to drag and overheat. 

What to do

• Do not drive the vehicle if possible: A failing ABS module can compromise your braking ability and other safety systems. It's best to have the vehicle towed to a mechanic to avoid further damage or risk. 
• Have it diagnosed immediately: A professional can use an OBD-II scanner to read specific diagnostic trouble codes from the ABS module and identify the problem. 
• Perform a visual inspection: Look for physical damage, loose connections, or corrosion around the ABS module and wiring before assuming a component failure. 

What happens when the ABS control module goes bad?

When an ABS module goes bad, it can cause the ABS warning light to turn on, leading to issues like longer stopping distances, brake pedal problems, and potential wheel lock-up during hard braking. In some cases, a faulty ABS module can also affect the speedometer, make strange noises, or cause the ABS pump to run constantly. The vehicle's normal braking function remains, but the safety benefit of the anti-lock system is lost.
 
This video explains the symptoms of a failing ABS control module: 53sCar FixYouTube · Apr 7, 2025
Common symptoms

• ABS warning light: The ABS light on the dashboard will illuminate, often disabling the ABS system completely. 
• Brake pedal issues: The brake pedal may feel unresponsive, requiring more force, or feel hard to press. 
• Wheel lock-up: During hard braking, the wheels may lock up and skid, which the ABS system is designed to prevent. 
• Increased stopping distance: The vehicle may take longer to come to a complete stop than it should. 
• Strange noises: You may hear grinding, buzzing, or other unusual noises from the braking system. 
• Speedometer problems: The speedometer may stop working correctly, show the wrong speed, or display 000 mph. 
• Constant pump noise: The ABS pump may run constantly even when you are not braking, which can drain the battery and lead to pump failure. 
• Traction control issues: Since traction control often relies on ABS sensors, it may also malfunction. 

You can watch this video to learn about the symptoms of a bad ABS module and how to diagnose it: 54sEasyAutoFixYouTube · Aug 13, 2022
What to do

• Have the vehicle diagnosed by a professional immediately.
• If the issue is severe, it's best to pull over safely and have the vehicle towed.
• Do not drive with a malfunctioning ABS module, as it compromises your vehicle's safety features. 

What are the symptoms of a bad ABS relay?

Check for these signs of a failing ABS.

• Unresponsive brake pedal. When you hit the brakes, does your car slow down?
• Applying more force to achieve the same level of braking.
• Your ABS warning light turns on.
• Your brakes are locking.

How do I know if my ABS fuse is blown?

A blown ABS fuse can cause the ABS warning light to illuminate on the dashboard, and it will disable the anti-lock braking system, meaning the wheels could lock up during sudden stops. Other symptoms include an increased braking distance, a firm or unresponsive brake pedal, and potentially erratic braking behavior.
 
Common symptoms

• Illuminated ABS warning light: This is the most common and direct sign, as the light on the dashboard will come on to indicate a system fault. 
• Wheel lock-up: Without power from a working fuse, the ABS cannot prevent wheels from locking up during hard braking or on slippery surfaces. 
• Increased stopping distance: The anti-lock system is designed to improve braking performance; a blown fuse will reduce or eliminate this benefit, potentially leading to longer stopping distances. 
• Hard or unresponsive brake pedal: A blown fuse can cause the brake pedal to feel unusually firm or slow to respond, requiring more pressure to slow the vehicle. 
• Erratic braking: In some cases, the system may behave strangely or inconsistently before the fuse fails completely. 

What to do

• Do not ignore the problem: A blown ABS fuse compromises your vehicle's safety systems. Driving with a failed ABS can increase your risk of losing control. 
• Inspect the fuse: Visually check the fuse in your vehicle's fuse box. A blown fuse will have a visibly broken wire inside. 
• Replace the fuse: If the fuse is blown, replace it with one of the same amperage rating. Ensure the vehicle is turned off before doing so. 
• Seek professional help: If the new fuse blows immediately or if the symptoms persist, there is likely a larger problem in the electrical system, such as a short circuit or a failing ABS component, that needs to be diagnosed by a mechanic.