Quick Answer: P0339 means the PCM is getting an intermittent signal from the crankshaft position sensor. On the Jeep JK this usually causes random stalling or hard starting, and the fix is almost always a new crankshaft position sensor.
Technical scope and sources
A diagnostic trouble code identifies a condition the vehicle detected; it does not, by itself, prove that one component must be replaced. Confirm related codes, symptoms, wiring/connectors, operating data and the exact vehicle configuration before selecting a repair. If a warning is flashing, the vehicle stalls, loses safe operation, or the diagnosis is uncertain, stop and seek qualified help. For basic vehicle information and maintenance context, consult 2018 Jeep Wrangler JK Owner’s Manual and Mopar’s JK maintenance schedule; use the correct model-year factory service information for diagnostic procedures. See the OffroadMe editorial standards for our technical scope.
What Does Code P0339 Mean?
P0339 (Crankshaft Position Sensor “A” Circuit Intermittent) is set when the crank sensor signal cuts out momentarily. The PCM relies on this signal for spark and fuel timing, so a dropout can cause the engine to stumble, stall, or refuse to start — often when the engine is hot.
Symptoms
- Intermittent stalling, especially once the engine is warm
- Hard starting or an occasional no-start
- A brief tachometer drop to zero while running
- Check-engine light that may come and go
Common Causes on the Jeep JK
- A failing crankshaft position sensor (the usual cause, often heat-related)
- Damaged wiring or a corroded connector at the sensor
- Rarely, a damaged reluctor ring on the crank
How to Diagnose It
- Scan for the signal dropping out, particularly when the engine is hot
- Inspect the sensor connector and harness for damage or corrosion
- Measure sensor resistance against specification
- Recreate the fault with a heat gun near the sensor if it is intermittent
How to Fix It
Replace the crankshaft position sensor and repair any damaged wiring or connector. Clear the code and confirm a stable signal and normal starting when hot.
Recommended Parts & Tools
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- Crankshaft position sensor — the direct fix for P0339
- Contact cleaner + dielectric grease — clean and protect the connector
- Bluetooth OBD2 scanner — watch for the signal dropout live