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DTC codes / C00xx · Brakes, steering and suspension / C0039

C0039Right Rear Tone Wheel

C0039 indicates that the anti-lock brake system (ABS) control module has detected a fault with the right rear tone wheel, which is the toothed ring mounted on the hub or axle that the wheel speed sensor reads. The module monitors the signal from the right rear wheel speed sensor and sets this code when the tone wheel's teeth are damaged, missing, or contaminated, causing an erratic or absent signal.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • ABS warning light illuminated on the dashboard
  • Traction control or stability control warning light may also be on
  • Often no symptoms besides the warning light, with normal braking performance
  • ABS may deactivate, leading to wheel lockup during hard braking
  • Possible intermittent operation of the speedometer or cruise control if the signal is erratic

Common causes, most likely first

  1. Corroded or dirty tone wheel, especially from road salt and debris
  2. Damaged or missing teeth on the tone wheel from impact or wear
  3. Loose or improperly installed tone wheel
  4. Wheel speed sensor air gap incorrect due to bent tone wheel or mounting issue
  5. Debris stuck between the tone wheel and sensor
  6. Failed wheel speed sensor (though usually sets a sensor-specific code)
  7. Wiring or connector issue at the right rear sensor

How to diagnose and fix it

  1. Inspect the right rear tone wheel for debris, corrosion, or damage after removing the wheel
  2. Clean the tone wheel and sensor area with brake cleaner and a soft brush
  3. Check the air gap between the sensor and tone wheel with a feeler gauge and compare to specification
  4. Test the wheel speed sensor with a multimeter for resistance and AC voltage output while spinning the wheel
  5. Inspect the sensor wiring and connector for corrosion or damage
  6. Replace the tone wheel if teeth are damaged or missing
  7. Clear the code and perform a road test to verify the repair

Tone wheel faults often misdiagnosed

  • A dirty tone wheel is a far more common cause than a failed sensor, so clean the ring before condemning any parts.
  • The right rear tone wheel is often damaged by road debris or improper wheel removal, so check for bent or missing teeth.
  • A worn wheel bearing can cause excessive play that alters the air gap and sets this code, so inspect bearing condition.
  • Corrosion under the sensor mounting surface can lift the sensor and change the air gap, mimicking a tone wheel fault.
  • Some vehicles use a magnetic encoder ring in the hub that can be contaminated by metallic debris, requiring hub replacement.

Can I keep driving with C0039?

The vehicle remains safe to drive under normal conditions because the base brakes still function, but avoid hard braking or slippery surfaces where ABS would normally engage. Have the fault diagnosed soon to restore full ABS and stability control operation.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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