How To Check If The ABS Speed Sensor Is Damaged?

Checking whether ABS speed sensor are damaged is a key step to ensure the vehicle's braking system is working properly. The following are systematic, professional inspection process and methods:
1.Initial observation and diagnosis
Instrument panel malfunction light inspection
Phenomenon: After the vehicle starts, if the ABS fault indicator continues to go on (it doesn't go out), it may indicate a sensor or system failure.
Note: ABS failure lights on some models may be shared with brake system warning lights (such as "BRAKE" lights) and need to be judged in conjunction with other symptoms.
Braking performance test
Emergency braking test: Emergency braking at higher speeds (e.g. 40-50km/h) on safe, clear routessuch as closed roads.
Normal performance: When ABS works, the brake pedal vibrate quickly, the steering wheel jiggles slightly and the wheels don't lock completely.
Abnormal performance: If the wheels are locked, the vehicle has a noticeable slip or loss of control, indicating a possible ABS malfunction and sensor problems.
Brake distance comparison: Emergency braking distance can increase significantly when ABS breaks down, especially if the road is slippery.
2. Physical inspection
Sensor appearance checks
Location: ABS sensors are usually installed near wheels (such as wheel hub bearings and steering knuckles).
Inspection content:
Are there oil, iron filings, mud or other contaminants on the surface of the sensor that may affect the transmission of the signal?
Is the sensor housing cracks, damaged or deformed?
Are sensor plug loose, corroded or in poor contact?
Teeth ring (signal wheel) inspection
Location: gear ring are usually combined with wheel bearing or semi-axles.
Inspection content:
Is the gear ring missing teeth, deformation or dirt, which may lead to abnormal sensor signals?
Is the clearance between the gear ring and the sensor up to (usually 0.5-1.5 mm)? Too large or too small a gap can affect the signal.
Wire harness checks
Inspection content:
Are wiring harness damaged, broken or aging?
Does the wiring harness rub against the wheel or chassis components, causing the insulation layer to wear out?
Are plug connection secure, any looseness or corrosive?
3. Electrical inspection
Resistance measurement
Tool: Multimeter.
Method:
Disconnect the sensor plug and measure resistance value at both ends of the sensor.
Standard values: sensor resistance value values may vary from model to model, usually ranging from a few hundred to a few thousand Ohm (e.g., 800-1500 Ω).
Judgement: If the resistance value above the standard range or infinite (open circuit), it means the sensor is damaged or destroyed.
Voltage measurement
Tool: Multimeter.
Method:
Connect sensor plug, start vehicles, measure voltage between sensor signal line and ground wire.
Normal: Voltage should fluctuate within a range (e.g. 0.5-5V) when the wheels rotate.
Abnormality: If the voltage does not fluctuate or remains at 0 volts, the sensor or circuit may fail.
Signal waveform check
Tools: oscilloscopes.
Method:
Connect the oscilloscope probe to sensor signal line and observe the signal wave as the wheel rotates.
Normal waveform: It should be a square wave or sine wave, the frequency is proportional to the speed of the car.
Abnormal waveform: If the waveform is missing, distorted or abnormal in frequency, the sensor or gear ring may fail.
4. Diagnostic instrument detection
Read fault code.
Tools: OBD-II diagnostic instrument.
Method:
Connect the diagnostic device and read the fault code (DTC) of the ABS system.
Common fault codes:
C0035: Left front wheel speed sensor circuit fault.
C0040: Abnormal speed sensor signal for right front wheel.
C0265: ABS pump motor failure (may indirectly affect sensors).
Verdict: Find specific fault components according to the fault code.
Data flow analysis
Method:
Check the real-time data flow of the ABS system, such as the speed of each wheel, the status of sensor signal, etc., through the diagnostic instrument.
Judgment: If the wheel speed data is abnormal (such as continuous zeros or excessive fluctuations), it may be related to sensor failure.
V. Replacement test
Sensor replacement
Method:
If sensor damage is suspected, try replacing it with a known good sensor.
After replacement, retest the brake test and diagnostic test to observe if the fault is disappeared.
NOTE: When replacing sensors, make sure the model and specification are the same as the original vehicle.
Replace ring gears
Method:
If the ring is damaged, the entire wheel bearing or half-shaft assembly needs to be replaced.
After replacement, re-check sensor signal and braking performance.
VI. Overview of common fault causes.
Possible manifestations
Sensor contamination or damage ABS fault light, brake wheel locks, signal waveform abnormal.
Ring gear missing or deformed, ABS fault light on, wheel locks during braking, abnormal signal frequency.
Wire harness open or short circuit ABS fault indicator light, signal voltage does not fluctuate, diagnostics instrument reports circuit fault.
sensor gap is too large or too small. ABS fault indicator light, signal waveform distortion, brake performance reduced.
ABS control unit fault ABS fault indicator light on, multi-sensor signal abnormal, diagnostics report control unit failure.
VII. Maintenance recommendations.
Cleaning sensors and ring gears
If the sensor or ring gear is contaminated, wash it with detergent and make sure it is dry before reinstalling.
Replace damaged parts.
If the sensor, ring gear or wiring harness is damaged, the original part should be replaced in a timely manner.
Adjust sensor gap.
If the gap is too large or too small, it should be adjusted to a standard value in accordance with the maintenance manual.
Professional maintenance
If the cause of the fault cannot be determined, it is recommended to go to a professional repair shop to avoid taking it down yourself, causing further problems.
VIII. Preventive measures
Regular inspections
Check the status of ABS sensors and ring gear regularly to remove contaminants.
Avoid bad road conditions.
Try to avoid driving at high speed in bad road conditions such as mud and sand to reduce the wear and tear of sensors and ring gear.
Timely maintenance
If the ABS fault indicator light is found to be on, it should be repaired in time to avoid affecting driving safety.
Through these steps, you can check ABS speed sensor thoroughly and systematically for damage and take appropriate maintenance measures. ABS system is an important part of vehicle braking safety. Regular maintenance and inspections are recommended to ensure its proper operation.