C0039 — Right Rear Tone Wheel (Subfault)

Causes

• Damaged or missing teeth on the right-rear tone wheel (reluctor ring).
• Contaminated tone wheel (metal debris, heavy rust, brake dust) preventing clear signal.
• Right-rear wheel speed sensor (ABS sensor) failed or out of position / loose.
• Connector corrosion, broken wires, or poor ground in the sensor circuit.
• Faulty ABS/ESC control module or internal circuit fault.
• Excessive wheel bearing play or damaged hub affecting tone wheel clearance.

Symptoms

• ABS, ESC or traction control warning lamp illuminated.
• Loss of ABS or traction control function for events involving the right-rear wheel.
• Inconsistent or erratic wheel speed reading for the right-rear wheel on a scan tool.
• Brake pedal pulsation or unusual brake behavior under ABS activation (rare).
• Possible noise or play from the rear hub/wheel bearing area.

What to check

• Read and record all stored codes and freeze frame data with a proper scan tool.
• Visually inspect the right-rear tone wheel/reluctor ring for damage, missing teeth, or heavy contamination.
• Inspect the wheel speed sensor for damage and correct seating; check sensor air gap to tone ring per service manual.
• Check sensor connector for corrosion, bent pins, water intrusion, or loose fit.
• Perform a wiggle test on the wiring from the sensor to the ABS module while monitoring the wheel speed signal for dropouts.
• Measure sensor resistance and compare to manufacturer specification (or check for open/short).

Signal parameters

• Identify sensor type from service data (Hall-effect/active type or passive/variable reluctance).
• Hall/active sensor: has a reference supply and produces a square/switching signal (logic-level pulses). Expect a supply reference (typically 5 V or vehicle-specific) and a pulsed output when wheel rotates; check service manual for levels.
• Variable reluctance sensor: generates an AC sinusoidal voltage whose amplitude increases with wheel speed; no supply line — measured as AC voltage across sensor terminals.
• Typical checks: with wheel off ground, spin wheel slowly and observe live data for a steady increasing pulse rate and stable amplitude; use an oscilloscope to confirm waveform and amplitude if available.
• Refer to OEM service manual for exact resistance, voltage and waveform specifications before replacing components.

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