The ABS light is one of the most common dash lights to come on at higher mileage, closely followed by the dreaded Check Engine light. Dealerships know that they can’t sell a car with either of them illuminated. Owners know that getting them turned off usually means big money, or some quality time in the garage. Here are three starting-points for ABS light diagnosis that will guide you in the right direction to finding the problem and fixing it right the first time.
1: Severed ABS Sensor Wire
Cars are meant to be driven, and this means four-season operation for many owners. Road hazards like ice chunks, rocks, and construction debris will enter a vehicle’s wheel well at least a few times a year, and the ABS sensor wire is the most fragile item in this area.
Look for slices in the ABS sensor’s jacket or bright bare copper exposed along the wire when inspecting the system.
2: Bad Wheel Bearing
A wheel bearing isn’t often considered an ABS component, but it directly involves it and if failed, will throw the system into error mode. If a wheel bearing is significantly worn to the point where the wheel can wobble about its axis, more than likely an ABS speed sensor code will be stored. Why?
Tone rings (or reluctor rings depending on the vehicle) are often mounted to the axle shaft of front-wheel and all-wheel drive vehicles. If the wheel speed sensor is mounted on the vehicle’s hub, it is spaced a specific distance away from the spinning ring on the axle. When the wheel bearing has failed catastrophically, the axle and therefore the ring will wobble around, altering this specification and causing the speed sensor to exhibit brief periods of no signal. In extreme cases, the axle can come in contact with the wheel speed sensor, effectively damaging it beyond usability.
3: Bad ABS Module
The ABS module is the main brain of the ABS system. It receives speed signals from each ABS sensor, knows when the Brake pedal is depressed, and can modulate the Brake pressure at all four wheels individually in a panic stop. With this clever ability comes a bit of complexity. The circuit board in an ABS module is jam packed with components and pins from each of the sensor inputs. Extreme heat and cold in a vehicle’s engine bay expands and contracts the internals of the ABS module, sometimes causing vital electronic solder joints to crack and become disconnected. If the entire ABS system looks good, but there’s a bad wheel speed sensor or ABS pump fault code, consider the ABS module.
Anti-lock Brakes are one of the many systems on a vehicle that are all-or-nothing. This means that like an airbag system, if one part of the system is faulty, the entire feature will disable itself in the name of safety.
An illuminated ABS light can indicate a multitude of failures just as a check engine light would. A good place to start diagnosis is at the ABS wheel speed sensors.
Physical Sensor Damage
Without a scan tool capable of reading ABS codes, a visual inspection is the easiest thing to do when diagnosing an ABS light. ABS sensor wiring can be inspected from underneath a vehicle that is safely supported on ramps – you may not even need to take the wheels off. If any sensor wires are frayed, corroded, or completely broken – problem found.
Dirty Sensor
ABS sensors can accumulate ferrous deposits or dirt that will impede their ability to read speed information. Removing the sensor is the best way to clean it, and in most cases, chemicals are unneeded. When cleaning fails, testing via multimeter or ABS scan tool is the next step.
Testing Sensors
If all looks good, it is still possible for an ABS sensor to fail internally. With an ABS sensor disconnected you can probe the terminals with a multimeter, eliminating the need to remove the sensor from the vehicle. Both passive (2-wire) and active (2 or 3-wire) ABS sensors can be tested for basic functionality with a multimeter. Research which type of sensor your vehicle has before proceeding.
Most vehicles allow access to the ABS sensor harness inside the cabin, rather than having to jack the car up and take a wheel off. For front sensors, check near the inner strut towers – this is where the ABS sensor wires usually intrude into the engine bay. For rear sensors, under the rear seat cushion or inside the trunk are the common junction points.
On a passive ABS sensor, measuring resistance across the signal and ground leads generally produces a reading of 800-2000 ohms. A steady reading within this range indicates a good sensor. If the resistance is constantly changing or increasing on the meter, the sensor is faulty. An internal short, a cracked housing, or moisture intrusion are just a few reasons why a sensor may have failed.
If the multimeter indicates an open (no resistance) or short circuit, this is another indication that the sensor is faulty. A replacement Holstein ABS sensor should be purchased prior to removing the bad sensor to keep the vehicle drivable. Holstein Sensors match the fit form and function of OE sensors at a more competitive price than the Dealer.
Diagnose and test first
An ABS light can indicate many things from pump failure to a dirty wheel speed sensor. A DIY’er can save money on parts and labor by gathering a successful diagnosis through proper testing and inspection procedures. Before taking a vehicle to the dealer, consider the DIY approach – most ABS faults can be fixed easily on your own for a fraction of dealer or independent shop rates.
Vehicles have become increasingly more complex in the last ten years, with new technology being flooded into our cars at an astonishing rate. In the early nineties it was strange to see an airbag implemented into a vehicle, now, it is hard to find a new car without a backup camera and anything less than six airbags installed.
When unnecessary electronics fail in a vehicle, there are always owners that express their desire to own a simple vehicle that isn’t equipped with these extraneous features. When things like heated seats or air pumps fail in older European vehicles, that is likely the end of it. The cost to fix such items often exceeds what the owner is willing to spend. If the car gets them from point A to point B, it has done its job. If ABS fails, is there an urgent need to repair the system, or can it be left with an illuminated ABS light for the life of the vehicle?
ABS should be repaired, eventually
Anti-lock Brakes became a staple of the automotive spec-sheet in the early 2000s, no longer becoming an option but a standard feature. Today, it is hard to find anything without anti-lock Brakes, as it is a mandatory safety feature on all new cars. With so many vehicles equipped with ABS, eventual failure of these components is imminent. If many state inspections don’t require the ABS system to be functional to pass, don’t assume that this system isn’t as important as the engine or suspension.
A common ABS error is a wheel speed sensor fault. Unlike an oil light or temperature gauge indicating an overheat condition, there is no need pull over immediately and park the vehicle. The great part about anti-lock Brakes is that the car is always utilizing the hydraulic braking system no matter what state the ABS is in. As long as the mechanical Brake hardware is intact and safe, (calipers, pads, rotors) the Brakes should always work towards bringing the vehicle to a stop.
Working Brakes without ABS?
When an ABS fault is indicated by an illuminated dash light, there is no need to panic, but action should eventually be taken. For example, if an ABS sensor has a broken wire, the entire ABS system will be disabled since the initial self-test will not succeed. Depending on the season and frequency of poor surface conditions in your area, this will matter to some more than others. In the winter, braking on any slippery surface will be as if the vehicle isn’t equipped with ABS at all: Locked wheels, no steering, and decreased control. But, the Brakes still have all the functionality they were equipped with from the factory, just no electronic ability to help the driver in a bad situation.
The ABS light is yellow for a reason – it indicates that caution should be taken while driving the vehicle, but there is no imminent need to stop. It is wise to get the system checked out sooner than later, but waiting until your next paycheck isn’t a bad timeframe. Just be aware of your vehicle’s limitations with the ABS system disabled and drive accordingly.
The anti-lock Brake system is a complex configuration of computers and sensors. When all of the components are working in perfect harmony, it ensures a quick, reactive system that can improve braking control under all surface conditions. Faults in this system are often first indicated by illuminated lights in the gauge cluster. On most vehicles, only the ABS light will illuminate when a fault is detected. What if your car or truck has both the ABS & Brake lights illuminated?
Two Different Lights, Two Different Meanings
The “Brake” light has always meant one simple thing: There is a fault with the braking system. Most commonly, this light is triggered by low Brake fluid or an engaged parking Brake. However on some vehicles, it can simply indicate a problem elsewhere in the system and can be illuminated immediately if there is an ABS fault.
The ABS light differs from the Brake light as it is usually controlled by a computer module. When this light is on, there are often trouble codes stored to help the owner or a technician diagnose the source of the fault in the anti-lock braking system.
The Brake light on most vehicles is activated by a simple circuit involving only one or two components. Usually, the Brake fluid level sensor and the parking Brake are the only two items that can activate the Brake light. But, not all vehicles are the same, and some of the earliest ABS systems would trigger both lights simultaneously for any ABS fault. Common Triggers
It is important to know what to look for when diagnosing the cause of one or both of these lights illuminating on your vehicle. Each light has their own set of triggers; and some shared between the two, and some not.
ABS light:
- Low battery voltage (computer not getting enough voltage)
- Broken wheel speed sensor wire
- Bad wheel bearing
- Dirty tone ring Bad ABS module
Brake light:
- Low Brake fluid
- Low Brake pads
- Parking Brake set
- Any ABS fault (illuminated in tandem with ABS light on certain vehicles)
Depending on the year of the vehicle, most ABS codes can be read by OBDII-based diagnostic tools on ‘96+ vehicles. On older vehicles or in special cases, a make-specific tool must be used, often owned by dealerships or independent shops.
No matter which light is on, don’t ignore it for too long. An illuminated ABS or Brake light is not only a minor annoyance but can affect resale and trade-in value, as well as raise a few eyebrows when it comes time to get the vehicle inspected. (State laws may vary) With a keen eye and a DIY approach, most ABS and Brake system repairs can be done at home.