What Does P0338 Mean?
The crankshaft position sensor A circuit is sending an abnormally high voltage signal to the ECM. The signal voltage exceeds the maximum expected value, which could indicate a short to voltage, sensor failure, or wiring issue. The engine may exhibit misfires, rough running, incorrect timing, or may stall because the ECM cannot accurately determine crankshaft position from the erroneous high signal.
Safety Warning
Do not drive if the engine is misfiring or stalling. A corrupted high CKP signal can cause severely incorrect ignition timing, which may lead to engine damage from detonation or unexpected stalling. Have the vehicle towed if drivability symptoms are significant.
Common Causes
35%
Short to battery voltage in the CKP sensor signal wire due to wiring harness damage
30%
Failed CKP sensor with internal short producing excessive output voltage
15%
Wiring harness routing too close to high-voltage ignition components causing inductive coupling
10%
Faulty ECM pull-down circuit for the CKP sensor input allowing voltage to float high
10%
Incorrect replacement CKP sensor with wrong signal output characteristics for the application
Diagnostic Steps
1
Monitor the CKP sensor voltage on live data — identify whether the signal is constantly high (short to voltage) or intermittently spiking (interference or failing sensor).
2
Disconnect the CKP sensor and measure voltage on the signal wire at the ECM connector — if voltage is still high with the sensor unplugged, the short to voltage is in the wiring, not the sensor.
3
Inspect the CKP sensor harness for damaged insulation where it routes near the starter motor, alternator, or ignition coils — these are common sources of voltage shorts and interference.
4
With the sensor disconnected, check signal wire resistance to battery positive and to all adjacent wires in the harness — any low resistance reading reveals a short.
5
If wiring checks are clean, test the CKP sensor output with an oscilloscope while cranking the engine — the waveform amplitude should match manufacturer specifications (typically 0.3–1.0V AC for magnetic sensors at cranking speed).
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The crankshaft position sensor A circuit is sending an abnormally high voltage signal to the ECM. The signal voltage exceeds the maximum expected value, which could indicate a short to voltage, sensor failure, or wiring issue. The engine may exhibit misfires, rough running, incorrect timing, or may ...
The most common cause of P0338 (Crankshaft Position Sensor A Circuit High Input) is: Short to battery voltage in the CKP sensor signal wire due to wiring harness damage
Typical repair costs for P0338 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Do not drive if the engine is misfiring or stalling. A corrupted high CKP signal can cause severely incorrect ignition timing, which may lead to engine damage from detonation or unexpected stalling. Have the vehicle towed if drivability symptoms are significant.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0338 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Ignition System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
