Tone Wheel
The toothed or magnetically striped ring that turns with the hub and gives a wheel speed sensor something to count. Also called a reluctor ring, exciter ring or ABS ring.
It is half of the wheel speed measurement and it is the half people forget, which is why sensors are so often replaced twice on one fault. The sensor is only a pickup; if the ring is damaged the signal is wrong no matter how good the sensor is.
How it fails is mechanical, and visible. A ring pressed onto a hub or driveshaft can be lifted and split by rust forming underneath. A tooth can be knocked off while a driveshaft or hub is refitted. Debris packed between the teeth reads exactly like a missing tooth.
The modern kind is easy to damage and easy to miss. Many are a magnetic encoder moulded into the back of the wheel bearing seal — a black band that looks like rubber. It can be wiped, scratched or demagnetised during a bearing change, and there is nothing to see afterwards.
Look before buying. Turning the wheel slowly by hand while watching the live sensor reading finds a damaged ring in minutes: the fault repeats at the same point in every revolution.
Also known as: reluctor ring, exciter ring, abs ring, tone ring, pulse ring, trigger wheel, encoder ring, magnetic encoder
Referenced by 39 codes
Codes involving this component (39)
- C0030 Left Front Tone Wheel Moderate
- C0031 Left Front Wheel Speed Sensor Moderate
- C0033 Right Front Tone Wheel Moderate
- C0034 Right Front Wheel Speed Sensor Moderate
- C0036 Left Rear Tone Wheel Moderate
- C0037 Left Rear Wheel Speed Sensor Moderate
- C0039 Right Rear Tone Wheel Moderate
- C003A Right Rear Wheel Speed Sensor Moderate
- C003C Rear Tone Wheel Moderate
- C003D Rear Wheel Speed Sensor Moderate
- P215C Output Shaft Speed - Wheel Speed Correlation Moderate
- C0500 Left Front Wheel Speed Sensor A Circuit/Open
- C0501 Left Front Wheel Speed Sensor A Range/Performance
- C0502 Left Front Wheel Speed Sensor A Circuit Low
- C0503 Left Front Wheel Speed Sensor A Circuit High
- C0504 Left Front Wheel Speed Sensor A Intermittent/Erratic
- C0505 Left Front Wheel Speed Sensor A Correlation
- C0506 Right Front Wheel Speed Sensor A Circuit/Open
- C0507 Right Front Wheel Speed Sensor A Range/Performance
- C0508 Right Front Wheel Speed Sensor A Circuit Low
- C0509 Right Front Wheel Speed Sensor A Circuit High
- C050A Right Front Wheel Speed Sensor A Intermittent/Erratic
- C050B Right Front Wheel Speed Sensor A Correlation
- C050C Left Rear Wheel Speed Sensor A Circuit/Open
- C050D Left Rear Wheel Speed Sensor A Range/Performance
Other components in Braking, Steering and Suspension
- Brake Booster 92
- Wheel Speed Sensor 72
- ABS Hydraulic Modulator 69
- Brake Pressure Sensor 42
- Yaw Rate Sensor 28
- Brake Pedal Position Sensor 23
- Steering Angle Sensor 21
- Electric Power Steering Motor 13
- Ride Height Sensor 7
- Tyre Pressure Sensor 5
- Electric Park Brake Actuator 4
- Park Brake Control Module 4
- Air Suspension Compressor 3
- Brake Fluid Level Sensor 2
- Brake Pad Wear Sensor 2
- Traction Control Switch 2
- Brake Caliper 1
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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