PRNDL Input #3 Circuit Failure
The transmission control module can't properly read which gear you've selected (Park, Reverse, Neutral, Drive, Low) because the sensor signal wire is broken or disconnected. It's like a light switch that doesn't send the on/off signal to the bulb.
The ECM monitors the PRNDL (Park-Reverse-Neutral-Drive-Low) input circuit #3 for valid voltage signals from the transmission range sensor. The sensor should produce distinct voltage levels for each gear position. A circuit failure means the ECM detects an open circuit, short, or voltage outside expected parameters.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| PRNDL Circuit #3 Voltage | 0.5–4.5V (varies by gear position) | No signal, continuous high/low, or erratic fluctuation |
| Signal Continuity | Circuit resistance < 5 ohms | Open circuit or > 10 ohms resistance |
Code C1860 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, C1860 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.