ABS Sensors and ABS Wheel Speed Sensors
ABS sensors are the wheel speed sensors that tell your anti-lock braking system how fast each wheel is turning, and Easy Life Markets sells them as front and rear replacements listed by vehicle, position and part number. If your ABS warning light is on, the traction control light has come on with it, or a scan tool shows a wheel speed fault, a failed sensor or its wiring is one of the most common causes.
What should you buy? Find the sensor for your exact vehicle and the corner that has the fault: front or rear, left or right. Our current range includes ABS sensors for BMW 3 Series, 4 Series, 2 Series and X3 models, Mercedes-Benz W220 and W221, Honda Civic and Acura EL, and a pair for Audi Q7, Porsche Cayenne and Volkswagen Touareg. Each listing gives the part numbers, so you can compare them with the sensor on your vehicle.
What ABS Sensors Do
An anti-lock braking system stops the wheels locking under hard braking, so you can still steer. To do that, the ABS control unit needs to know the speed of every wheel, many times a second. Each wheel has a sensor that reads a toothed or magnetic ring turning with the hub, driveshaft or axle. The control unit compares the signals. If one wheel slows much faster than the others, it is about to lock, and the unit briefly eases the brake pressure on that wheel. You can read more about the system on the anti-lock braking system page on Wikipedia.
The same signals feed other systems. Traction control, stability control, hill start assist and, on some cars, the speedometer and the tyre pressure warning use wheel speed data. That is why one failed sensor can switch on several warning lights at once.
When a sensor fails, the brakes still work as normal brakes. What you lose is the anti-lock function and the systems that depend on it. That is still a safety issue, and it should be fixed promptly.
Types of ABS Sensors
All ABS sensors do the same job, but they are built in two main ways. Knowing which kind your car uses helps when testing and ordering.
Passive (inductive) ABS sensors
A passive sensor has a magnet and a coil of wire. As the teeth of a metal tone ring pass the tip, they create a small alternating voltage. The faster the wheel turns, the higher the frequency. Passive sensors are simple and were common on older vehicles. They have two wires and need no power supply. At very low speeds their signal is weak, which is one reason newer cars moved to active designs.
Active (Hall effect or magnetoresistive) ABS sensors
An active sensor is powered by the control unit and gives a clean digital signal, even at walking pace. It reads either a toothed ring or a magnetic encoder ring built into the wheel bearing seal. Most modern cars use active sensors. They can be more sensitive to the gap and to damage on the encoder ring, so when you fit one, inspect the ring as well.
Front and rear ABS sensors
Front sensors usually mount in the steering knuckle or hub. Rear sensors mount in the hub carrier, the axle housing or near the differential, depending on the vehicle. Front and rear parts are rarely the same. Some sensors fit left or right on the same axle, while others are made for one side only. Our listings state this clearly, for example the 34526791225 rear ABS sensor for BMW fits rear left or right, while the Civic front left ABS sensor is for the front left only.
Our Current ABS Sensor Range
This collection lists ABS parts by vehicle and part number. Examples in our current range:
- BMW E46 rear ABS sensor 34526752683 for 3 Series E46 models, rear left or right.
- BMW E83 X3 front ABS sensor 34523420330 for X3 2004-2010, front left or right.
- BMW rear ABS sensor 34526791225 for models including 230i, 320i, 328i, 330i, 335i and 430i.
- Mercedes-Benz W220 front ABS sensor 2205400117, also listed for W215 models.
- Mercedes W221 rear ABS sensor 2215400117 for 2007-2010 models.
- 7P0927807 ABS sensor pair for Audi Q7, Porsche Cayenne and VW Touareg.
- Civic front left ABS sensor 57455S5D013 for Honda Civic 2001-2003 and Acura EL 2001-2004.
We plan to add more ABS sensors and related parts over time. Always read the full product page for the models and positions covered.
ABS Sensor Types Compared
| Feature | Passive (inductive) | Active (Hall or magnetoresistive) |
|---|---|---|
| Power supply | None, makes its own signal | Powered by the ABS control unit |
| Signal | Alternating voltage that rises with speed | Digital square wave |
| Low speed reading | Weak near standstill | Reads down to very low speed |
| Typical wires | Two | Two, sometimes three |
| Reads | Toothed metal ring | Toothed ring or magnetic encoder in the bearing |
| Common on | Older vehicles | Most modern vehicles |
| Testing | Resistance and AC voltage with a meter | Best checked with a scan tool or oscilloscope |
Signs of a Faulty ABS Sensor
Wheel speed sensors live in a harsh place, close to the brakes, the road and the water. These are the usual signs of trouble:
- ABS warning light on. The most common sign. Traction or stability lights often come on too.
- Warning light that comes and goes. This often points to a damaged cable or a loose plug rather than the sensor tip.
- ABS working when it should not. A pulsing pedal at low speed on a dry road can mean a sensor is giving a false reading.
- Speedometer or cruise control problems. On some vehicles, these use the same wheel speed data.
- A fault code for one wheel. A scan tool will usually name the corner, which tells you which sensor to check first.
Not every ABS light means a bad sensor. Damaged wiring, a dirty or cracked tone ring, too large an air gap, a worn wheel bearing or a problem in the control unit can cause the same warning. Read the fault code first. Our diagnostic equipment section is the place to look for scan tools.
How to Choose the Right ABS Sensor
- Read the fault code. It tells you which wheel to work on, and whether the fault is in the signal, the circuit or the sensor.
- Confirm the vehicle. Match the make, model, chassis code and year range. For BMW and Mercedes-Benz, the chassis code (such as E46, E83, W220 or W221) is the clearest guide.
- Confirm the position. Front or rear, and left, right or either side.
- Compare part numbers. Most ABS sensors carry a number on the body or the plug. Our listings show the numbers from the product page.
- Check the cable length and plug. Sensors for the same corner can come with different cable lengths for different variants.
- Look at the tone ring. If the ring is cracked, rusted or missing teeth, a new sensor alone will not fix the fault.
If you are unsure, send us your vehicle details and the old part number through our contact page before you order.
Testing ABS Sensors Before You Buy
A quick check before ordering can save money and time. The goal is to find out whether the sensor itself has failed, or whether the problem is the wiring, the ring or something else.
Visual check
Raise the vehicle safely and look at the sensor at the faulty corner. Follow the cable from the sensor to its plug. Look for cuts, melted insulation near the exhaust, stretched sections and corrosion in the plug. A cable that has been pulled tight by a worn suspension part is a common find. Check that the sensor is fully seated in its hole.
Scan tool check
A scan tool that reads ABS live data shows the speed of each wheel while you drive slowly. A healthy set of ABS sensors shows four similar readings. A sensor that reads zero, drops out or jumps around is suspect. This is the most useful test for active sensors, because their signal is hard to read with a basic meter.
Meter check for passive sensors
Passive sensors can often be checked with a multimeter. Measure the resistance across the two pins and compare with the figure in the vehicle's service information. With the wheel raised, spin it by hand and measure AC voltage. A reading that rises as the wheel turns faster shows the sensor is producing a signal. Do not use a meter on an active sensor without the correct procedure, as some testing methods can damage the circuit.
Tone Rings and Encoder Rings
The sensor is only half of the pair. It reads a ring that turns with the wheel. On many older cars this is a toothed steel ring pressed onto the driveshaft, hub or brake disc. On many newer cars, it is a magnetic encoder built into the wheel bearing seal, which you cannot see without removing parts.
Rings fail too. Steel rings can crack, rust and swell, or collect metal dust from the brakes. A magnetic ring can be damaged by a magnet, by impact or by a bearing fitted the wrong way round. If a new sensor does not fix the fault, the ring is the next thing to check. When fitting a new bearing on a car with a magnetic encoder, make sure the encoder side faces the sensor.
Replacing ABS Sensors
Replacing a wheel speed sensor is often a simple bolt-out, bolt-in job, but it sits on a safety system. We recommend professional fitting if you are not confident, and a professional should check the ABS system afterwards if any warning remains.
General good practice when replacing ABS sensors:
- Disconnect the plug first and follow the cable back to see how it is routed and clipped.
- Old sensors can seize in the hub. Use penetrating oil and patience. Twisting hard can break the sensor and leave the tip stuck.
- Clean the mounting hole of rust and dirt so the new sensor sits fully home. A raised sensor increases the air gap.
- Use a small amount of the grease or anti-seize the service manual recommends, if any, on the sensor body. Keep it off the tip.
- Route the new cable exactly like the old one, through every clip and grommet, clear of moving parts.
- Clear the fault codes with a scan tool, then test drive. Some vehicles clear the light on their own after a short drive.
While the wheel is off, take a look at the brake hose and the pads. Our brake lines section, pads section and calipers section carry related parts.
Care and Prevention
- Keep sensor cables clipped in place. A loose cable can rub on a tyre or flex until it breaks.
- Be careful when working on brakes and suspension. It is easy to pull or pinch a sensor cable.
- Wash mud and salt from the wheel arches. Corrosion around the mounting can push the sensor out of place.
- Replace a noisy wheel bearing promptly. A worn bearing lets the ring wobble and upsets the signal.
- After fitting new rotors or hubs, check that the sensor cable and plug are refitted correctly.
- Use only matched tyre sizes. Very different tyre sizes on one axle can confuse wheel speed readings.
ABS Sensors and the Wider Brake System
An ABS sensor is a small part of a larger system. The control unit and pump modulate pressure in the brake lines. The calipers and pads do the actual stopping. The rotors and hubs carry the tone rings on many cars. A healthy anti-lock system needs all these parts in good order. Browse the full brakes collection for the rest of the system, and our rotors and discs section if your discs are due as well.
Wheel speed sensors are also part of the car's electrical system. For other sensors, such as oxygen, camshaft and crankshaft position sensors, see our sensors section and the wider electrical collection. A good overview of how these parts read wheel speed is on the wheel speed sensor page on Wikipedia.
Who Shops for ABS Sensors at Easy Life Markets
Our customers include home mechanics with a scan tool, independent workshops and owners who order the part and have a mechanic fit it. Many drive European cars, where part numbers are the most reliable way to match a sensor. We list those numbers wherever the product page has them, so you can buy with confidence.
The current price and availability are shown on each product page. If you cannot find a sensor for your vehicle yet, browse the main auto parts catalogue or ask us.
Buying Tips
- Read and note the fault code before ordering.
- Photograph the old sensor, its plug and any numbers on it.
- Check the tone ring and the wiring while you are there.
- Order for the correct corner. A left-only part will not suit the right side.
- Read our shipping policy and return and refund policy before you order.
- Keep the new sensor in its packaging until you are ready to fit it, to protect the tip.
Frequently Asked Questions
Can I drive with the ABS light on?
Your normal brakes usually still work, but the anti-lock function and related systems may be off. Have the fault checked and fixed promptly, and drive with extra care until then.
How do I know which ABS sensor has failed?
A scan tool that reads ABS codes will usually name the wheel. Without one, inspect the cables and plugs at each corner for damage.
Are front and rear ABS sensors the same?
Usually not. Front and rear sensors differ in shape, length and plug. Some fit left or right on the same axle, others are side-specific. Check the listing.
Should I replace ABS sensors in pairs?
It is not usually required. Replace the faulty one. If both sensors on an axle are old and corroded, replacing both at once can save a second job. Our 7P0927807 sensors are sold as a pair.
Will a new sensor turn off the warning light?
If the sensor was the fault, the light should go out after the codes are cleared or after a short drive. If it stays on, check the wiring, the tone ring and the wheel bearing.
Can I fit ABS sensors myself?
Many owners can, with basic tools and care. Seized sensors and electrical faults can be tricky, so use a professional if you are unsure.
How do I check fitment?
Match the vehicle, chassis code, years, position and part numbers. Our FAQ page covers ordering, and you can contact us for help.