C0669 indicates the ABS/ESC module has detected an abnormally high voltage, open circuit, or high resistance in the right rear wheel speed sensor "B" circuit. The module therefore cannot trust the wheel speed signal, which can disable ABS, traction control, and stability control. The problem is most often in the sensor, its wiring, or the connector rather than the control module itself.
An internal open, short, or high-resistance failure inside the sensor can raise circuit voltage and prevent a clean speed signal. This is the single most common cause for this code.
Chafing, pinching, corrosion, or a poor pin connection can create a short to voltage, an open, or excessive resistance in the harness between the sensor and the ABS/ESC module.
A cracked, chipped, or contaminated reluctor ring, or an incorrect air gap, can produce a weak or erratic signal that the module interprets as a circuit fault.
Loose, spread, or pushed-back terminals at the sensor or module connector can intermittently raise circuit resistance and set a high-circuit code.
A rare internal failure of the ABS/ESC module can misread a normal sensor signal as high voltage; this should only be considered after the sensor, wiring, and connectors have been ruled out.
The vehicle usually remains drivable, but ABS, traction control, and stability control may be disabled or behave abnormally. It should be diagnosed and repaired as soon as practical.
Usually no. This code is most often caused by a wheel speed sensor, wiring, or connector problem. Replacing the ABS/ESC control module is rarely the correct fix and should only be done after thorough electrical testing rules out everything else.
The "B" designation typically refers to a specific circuit, signal path, or a secondary sensor on that corner. The exact meaning varies by manufacturer, so consult the service information for your vehicle.
"Circuit High" means the voltage or resistance in the sensor circuit is above the expected range. This commonly results from an open wire, high-resistance connection, or an internal sensor fault rather than a true over-voltage condition.