Crankshaft Position Sensor B Circuit High Input
The crankshaft position sensor B is sending a voltage signal that's too high, like a microphone stuck at maximum volume instead of reading engine speed normally. The ECU can't trust this signal to properly time ignition and fuel injection.
The ECU monitors the analog voltage output from crankshaft position sensor B, which should oscillate within a normal range as the engine rotates. When the voltage stays abnormally high (near battery voltage) instead of cycling properly, the ECU detects a circuit high condition and sets the fault code.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Output Voltage | 0.2–4.5V (cycling) | >4.5V (sustained high) |
| Signal Frequency | Proportional to RPM | Missing or erratic pulses |
Code P0389 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.
Once the fault is repaired, P0389 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.