Crankshaft Position Sensor A Circuit High
The Powertrain Control Module (PCM) detected that the voltage signal from the Crankshaft Position (CKP) Sensor 'A' circuit is higher than the manufacturer's specified maximum threshold. This typically indicates a short to voltage in the wiring or an internally shorted sensor that is failing to pull the voltage down during operation.
The crankshaft position sensor is critical for engine timing, spark, and fuel delivery. A failure in this circuit can cause the engine to stall unexpectedly while driving or prevent the vehicle from starting entirely, posing a significant safety risk.
Common symptoms
- Check Engine Light is illuminated
- Engine cranks but fails to start (no-start condition)
- Engine stalls unexpectedly while driving or idling
- Rough idling, misfires, or hesitation during acceleration
- Tachometer drops to zero or behaves erratically while the engine is running
Likely causes
- Faulty Crankshaft Position (CKP) sensor
- Short to voltage in the CKP sensor wiring harness
- Corroded, damaged, or loose connector at the CKP sensor
- Damaged reluctor ring (crankshaft tone ring) or metallic debris on the sensor tip
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Perform a visual inspection of the CKP sensor wiring and connector
Look for: Look for chafed wires, melted insulation, or corrosion in the connector that could cause a short to voltage or poor connection.
Monitor engine RPM data using a scan tool
Look for: Observe the engine RPM data PID while cranking the engine; a reading of 0 RPM indicates the PCM is not receiving a valid CKP signal.
Test the CKP sensor circuit for a short to voltage
Look for: Disconnect the sensor and measure the voltage on the signal wire with the key on; if it reads battery voltage or a steady 5V when it shouldn't, there is a short to power in the harness.
Measure the internal resistance of the CKP sensor (for VR type sensors)
Look for: Compare the sensor's resistance to factory specifications; an out-of-limits reading indicates an internal fault in the sensor.
Analyze the CKP signal using an oscilloscope
Look for: Back-probe the CKP signal wire while cranking to look for a proper waveform; a signal line that remains stuck at a high voltage instead of oscillating confirms the circuit high condition.
This page explains the generic P0338 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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