Crankshaft Position Sensor A Circuit Intermittent
Your engine's crankshaft position sensor is sending a weak or flickering signal to the computer, like a radio station that keeps cutting in and out. The engine needs this signal to know exactly when to fire the spark plugs, so an intermittent signal causes performance issues.
The ECM monitors the crankshaft position sensor signal voltage and frequency to calculate engine speed and cylinder position. When the signal drops below minimum voltage thresholds or becomes erratic, the ECM logs an intermittent fault. The sensor typically outputs a digital or analog signal that must remain stable within expected ranges.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Signal Voltage | 0.5–4.5V (varies by sensor type) | Below 0.2V or erratic switching |
| Signal Frequency/Continuity | Continuous at engine speed | Dropouts or missing pulses |
Code P0340 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, P0340 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.