Speed Wheel Sensor RR Input Open Circuit
The right rear wheel speed sensor isn't sending a signal to the engine computer, like a disconnected speedometer cable. This breaks the anti-lock brake system and traction control because the ECU can't monitor that wheel's speed.
The ECU monitors AC voltage pulses from the rear right wheel speed sensor as the wheel rotates. It expects a continuous signal within a specific frequency range proportional to vehicle speed. An open circuit produces zero signal or sporadic pulses below the minimum detection threshold.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Wheel speed sensor voltage | 0.5-2.0V AC (varying frequency) | No signal or <0.1V sustained |
| Signal frequency | 10-200 Hz depending on speed | Zero Hz or below minimum threshold |
Code C1166 is classified as a serious fault. If your check engine light is flashing — not just steady — pull over safely and do not continue driving. A flashing CEL indicates an active misfire or critical failure that can cause catalytic converter damage within minutes or permanent engine harm within miles. Contact a certified mechanic immediately. Do not attempt roadside repairs on high-severity codes unless you are trained to do so.
Once the fault is repaired, C1166 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.
The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.