Crankshaft Position Sensor A Circuit Low Input
The crankshaft position sensor is sending a weak electrical signal to the engine computer, like a radio station broadcasting too quietly. The ECU can't reliably detect engine position and timing, which disrupts fuel injection and ignition.
The ECU monitors the voltage signal from the crankshaft position sensor as the engine rotates. This signal triggers fuel injection and spark timing calculations. When the voltage drops below the minimum threshold, the ECU sets this fault code because it cannot reliably determine engine position.
| Parameter | Normal Range | Fault Condition |
|---|---|---|
| Sensor Signal Voltage | 0.3V to 5V with AC fluctuation | Below 0.3V or no signal detected |
| Signal Frequency | Engine RPM-dependent pattern | Missing or erratic pulses |
Code P0338 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, P0338 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.