C0125

Code

Generic C — Chassis

Right Rear Wheel Speed Sensor Circuit Malfunction

Brand: Generic

Type: C — Chassis

Views: UK: 15 EN: 24 RU: 12

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Page language: EN

Causes

Damaged or failed right rear wheel speed sensor
Broken, chafed or shorted wiring between sensor and ABS control module
Corroded/loose connector at the sensor or harness
Damaged or missing tone ring (reluctor ring) on hub/axle
Contaminated sensor (metal debris, grease) or sensor air gap out of specification
Faulty ABS/traction control module or poor module ground/power

Symptoms

ABS warning lamp illuminated on dash
Traction control or ESP/Stability warning lamps may illuminate or system disabled
ABS may not operate correctly under heavy braking (possible wheel lockup)
Inconsistent or zero wheel speed reading from right rear in scan tool live data
Possible reduced traction control performance or disabled cruise control

What to check

Read all stored DTCs and freeze frame data with a scan tool; note related codes
Check live wheel speed sensor PIDs at low speed and compare all four wheels
Visually inspect right rear wheel sensor, tone ring, hub, and connector for damage, corrosion or debris
Wiggle the sensor harness while watching live data for intermittent changes
Measure sensor resistance with multimeter (ohms) at connector and compare to spec or same-side sensor if available
Probe sensor connector for reference voltage/supply and ground (for active/Hall sensors) with ignition on

Signal parameters

Passive (VR) sensor: AC voltage waveform; amplitude increases with wheel speed (typical 0.1–1.5 VAC at low speed, higher at higher speed)
Active (Hall/effect) sensor: DC square wave or pulsed 0–5 V (sometimes 0–12 V depending on vehicle); has a reference (typically 5 V) and ground
Typical passive sensor resistance (varies by vehicle) often in the hundreds to thousands of ohms — compare to service spec or opposite wheel
Signal frequency increases linearly with wheel speed; loss of signal or missing pulses indicates a fault
Connector types commonly 2-pin (VR) or 3-pin (active) — check for proper pin voltages on 3-pin sensors (Vref, signal, ground)

Diagnostic algorithm

Verify C0125 is current; record freeze frame and any other related codes (ABS, wheel sensors, communications).
Connect scan tool and observe all four wheel speed sensor PIDs while slowly rotating the wheel (or road test at low speed) to confirm right rear shows no or erratic signal compared with other wheels.
Perform visual inspection: remove wheel if needed, inspect sensor tip and tone ring for damage, contamination, missing teeth, or excessive air gap. Clean if contaminated and recheck.
Inspect and flex the harness and connector while watching live data for intermittent changes. Repair/replace damaged harness or connector terminals as required.
Measure sensor resistance at the sensor leads (with harness disconnected) and compare to specification or opposite sensor. If open/shorted, replace sensor.
For passive sensors, spin the wheel and measure AC voltage across sensor leads; for active sensors, check Vref (with ignition on), ground, and signal while rotating wheel. Replace sensor if no proper output.
Perform continuity tests from sensor connector back to ABS module to detect opens, shorts to power or ground. Repair wiring faults as needed.
If wiring and sensor check good, verify ABS module power and ground circuits and test for stored module faults. If module is suspected, consult manufacturer procedures for module testing/reprogramming.
After repairs, clear codes, perform a road test or perform ABS activation tests using a scan tool and re-scan to confirm the fault does not return.