How do I know which ABS sensor needs replacing?

Identify the faulty ABS sensor with a diagnostic scan and live data. The wheel-speed sensor tied to the fault is the likely replacement, but you should confirm by inspecting wiring, the tone ring, and data from all wheels.

How the fault is identified

When the anti-lock braking system triggers a fault, the vehicle’s onboard computer (the ABS control module) stores trouble codes and often reports live wheel-speed readings. The combination of a code that points to a wheel (front left, front right, rear left, rear right) and suspicious live-data readings helps you zero in on the sensor that’s failing. If the code is ambiguous or the data isn’t clearly pointing to a single wheel, a systematic check is required to rule out wiring, connectors, and the tone ring in addition to the sensor itself.

To locate the faulty sensor, follow these diagnostic steps:

• Use an ABS-capable scan tool to pull DTCs from the ABS/ESP module and note the wheel location indicated by the code.


• View live wheel-speed data while the car is stationary and then during a controlled rotation of each wheel (or a road test) to see which wheel’s data is absent, erratic, or out of sync with the others.


• Clear the codes, drive or test again, and check if the fault code reappears to confirm persistence.

When the codes and live data consistently point to a specific wheel, that location is the primary candidate for further inspection and possible sensor replacement. If no single wheel clearly stands out, you’ll need to perform more thorough physical and electrical checks described below.

Interpreting codes and data

Codes that reference a wheel location or a sensor circuit usually indicate the suspect sensor or its wiring. Live data should show a stable reading from all wheels except the suspected one, which may show zero, infinite, or highly erratic readings. Modern systems may also flag a sensor circuit fault even if the wheel data looks nominal until load, speed, or turning conditions reveal the issue.

Physical inspection and environmental checks

Even if the code points to a sensor, environmental factors often cause faults. Inspect the entire wiring harness for abrasion, corrosion, or loose connections; check connectors for moisture or dirt; and examine the tone ring (reluctor) for cracks, chips, excessive rust, or misalignment, which can produce faulty signals even with a good sensor.

Physical and electrical checks to perform

Beyond the diagnostic codes, a hands-on inspection can reveal problems that software alone can miss. Use these checks to confirm the faulty location before purchasing a replacement sensor.

• Inspect wiring and connectors at the suspected wheel for damage, corrosion, or loose pins.


• Check the tone ring for damage, debris, or misalignment that could affect sensor readings.


• Measure sensor resistance with a digital multimeter if the sensor is of a passive type; compare against the vehicle’s service manual specifications (range varies by model). An open circuit or a resistance well outside spec usually indicates a failed sensor.


• Verify sensor power and ground continuity from the ABS control module using the appropriate wiring diagram and a test light or a multimeter while ensuring the ignition is off when probing.


• Look for abnormal wear or damage around the mounting area that could cause incorrect sensor positioning or vibration.

If any of these checks reveal a compromised wiring, a damaged tone ring, or a poor connection, fix those issues first. A sensor can read fine in isolation but still produce faults if the wiring or ring is compromised.

Replacement: when and how to replace the sensor

Once you’ve identified a faulty wheel-speed sensor, replacement generally follows a straightforward process, though exact steps vary by vehicle. Always consult your service manual for location-specific instructions and torque specs. If you’re unsure at any point, consider professional help, as ABS systems are critical to safe braking performance.

1. Prepare the vehicle: park on a level surface, engage the parking brake, chock wheels, and detach the negative battery terminal if recommended by your manual.


2. Lift the vehicle and remove the wheel on the suspected corner to access the sensor.


3. Disconnect the sensor wiring harness at the connector, then remove the sensor mounting bolts or housing. Some sensors thread into the hub/knuckle; others snap into place.


4. Inspect the mounting area and strip any old adhesive or debris from the sensor seat. Install the new sensor, ensuring proper orientation and alignment with the tone ring.


5. Reconnect the wiring harness securely, reinstall the wheel, and torque the lug nuts to spec. Lower the vehicle and reconnect the battery if it was disconnected.


6. Use the scan tool to clear ABS codes, then conduct a road test to confirm the warning light does not return and that wheel-speed data reads normally from all corners.

After replacement, perform a thorough test: a slow, controlled stop from various speeds to confirm the ABS engages correctly and that there are no lingering fault codes. If codes persist after replacement, re-check wiring and tone ring, or consider a more comprehensive ABS diagnostic.

What to watch for after replacement

Even with a new sensor, faults can recur if related components are neglected. Common culprits include damaged wiring, corroded connectors, a dirty or damaged tone ring, or a failing ABS control module. If the warning light comes back or if live data again shows irregular wheel speeds, re-run the diagnostic flow focusing on the suspect corner and verify there are no intermittent connections or mechanical misalignment.

Summary

Pinpointing the exact ABS sensor that needs replacing starts with an ABS-capable diagnostic scan to read fault codes and observe live wheel-speed data. Use the code location and data patterns to identify a suspect wheel, then verify with physical inspections of wiring, connectors, and the tone ring. If a replacement is necessary, follow a careful, vehicle-specific procedure and test thoroughly after installation to ensure the ABS system functions correctly and the warning light remains off. When in doubt, consult a qualified technician to avoid compromising braking safety.

How to find out which ABS sensor is faulty?

You can tell which ABS sensor is bad by using a diagnostic scanner to read fault codes or check live data, or by manually testing the sensor with a multimeter. A scanner will show a specific code for a failing sensor or a live data feed where one wheel's speed reading is incorrect (like staying at 0 mph while the others move). A manual test involves checking the sensor's resistance or voltage output with a multimeter, which will be out of specification or inconsistent for a bad sensor. 
Method 1: Using a diagnostic scanner

• Connect the scanner: Plug a compatible diagnostic scanner into your vehicle's OBD-II port. 
• Read fault codes: Access the ABS or chassis control module and read the diagnostic trouble codes (DTCs). The code will often point to a specific wheel speed sensor that is malfunctioning. 
• Check live data: Go to the "live data" or "data stream" option, specifically looking for wheel speed sensor readings (often labeled RPM sensors). 
• Spin the wheels: While a friend watches the scanner, have them spin each wheel (or, if possible, drive the car slowly). 
• Identify the faulty sensor: The sensor that shows a reading that is incorrect (e.g., stuck at 0 mph or an erratic number) is the one that is bad. 

Method 2: Using a multimeter

• Locate the sensor and disconnect it: Follow the wire from the wheel to its connector and unplug it. 
• Check for resistance: 
  • Set your multimeter to the "ohms" (Ωcap omegaΩ) setting. 
  • Connect the probes to the terminals on the harness side of the plug. 
  • You may need to use a specific tool or insert small wires to make contact if the terminals are deep. 
  • A good sensor will have a specific, steady resistance reading (often between 1.5 and 1.7 kiloohms, or 1500−1700 Ω1500 minus 1700 space cap omega1500−1700 Ω). 
  • If you get an "open" reading (OL) or a reading that is significantly different from your other sensors, the sensor is likely bad. 
• Check for AC voltage: 
  • If the resistance test passes, set the multimeter to the AC voltage setting. 
  • Reconnect the sensor's wiring connector. 
  • Spin the wheel manually as fast as you can. 
  • A good sensor will generate a voltage reading that fluctuates with the speed of the wheel. If the voltage remains at 0 or doesn't change, the sensor is likely bad. 

How do you know if you need a new ABS sensor?

How Can I Tell if My ABS Sensor Is Bad?

1. Your ABS light is on.
2. Your car is pulling to one side or veering when you brake.
3. Your brakes feel spongy or unresponsive.
4. You're experiencing longer stopping distances.

How to tell which brake sensor is bad?

You can tell which brake sensor is bad by diagnosing the specific symptoms it causes, using an OBD scanner to read trouble codes, and performing manual tests with a digital multimeter. Common signs include brake warning lights, non-functioning brake lights or cruise control, a stiff brake pedal, and longer stopping distances. An OBD scanner can directly tell you which wheel speed sensor is at fault, while a multimeter can confirm a bad wear sensor by checking for continuity.
 
This video demonstrates how to identify a bad brake pad wear sensor: 1mYOUCANICYouTube · Jan 21, 2022
By symptoms

• Brake and ABS warning lights: A lit dashboard light indicates a fault, and an OBD scanner can provide a specific code that points to a particular sensor. 
• Brake light issues: If your brake lights don't turn on, or they stay on all the time, the brake light switch (also called the brake pedal position sensor) is likely the culprit. 
• Cruise control problems: A faulty brake pedal position sensor can prevent your cruise control from working. 
• Stiff or long-travel brake pedal: A bad brake booster sensor can cause the brake pedal to feel hard to press, or the vehicle's stopping distance to increase. 

Using an OBD scanner 

• An OBD scanner is the most direct way to identify a faulty wheel speed sensor. 
• Plug the scanner into your vehicle's diagnostic port and read the codes. The code will often specify which sensor is failing, for example, "front left wheel speed sensor circuit," notes Quora users. 

This video explains the symptoms of a bad brake light switch: 49sEasyAutoFixYouTube · Aug 17, 2022
Using a digital multimeter 

• For brake pad wear sensors:
  • Unplug the sensor and set your multimeter to measure resistance or continuity (look for a beeping sound).
  • Touch the two leads of the sensor with the multimeter probes.
  • A beep (or continuity reading) means the sensor is good. No beep means the wire is broken, and the sensor is bad.
• For ABS wheel speed sensors:
  • Unplug the sensor and connect the multimeter probes to the sensor's terminals.
  • Set the multimeter to measure resistance (Ohmcap O h m𝑂ℎ𝑚, Ωcap omegaΩ).
  • A good sensor will show a steady resistance reading within a specific range (often 800-2000 Ωcap omegaΩ).
  • A reading that is constantly changing, higher than expected, or infinite (no reading) indicates a bad sensor. 

Can a scanner tell you which wheel speed sensor is bad?

A scanner watching live data when driving and replicating the concern will pinpoint which sensor is at fault. However it will need to be diagnosed first, as other components can and will cause issues.