Wheel Speed Sensor Center Tone Ring Missing Tooth Fault
Your wheel speed sensor detects a missing tooth on the tone ring, like a gear with a chunk broken out of it. The ABS system can't read speed properly at that wheel, causing safety and traction control issues.
The ECM monitors pulse patterns from the wheel speed sensor as the tone ring rotates past the magnetic pickup. It counts teeth per revolution and detects missing or irregular tooth spacing. When a tooth gap is identified, the sensor signal becomes erratic, triggering the fault.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Tooth count per revolution | Expected consistent pattern (typically 48 teeth) | Missing tooth detected; irregular pulse intervals exceed tolerance |
| Sensor signal frequency variance | <5% variation | >10% variation or complete signal dropout during tone ring pass |
Code C1139 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, C1139 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.