1999 Dodge Ram 1500 5.9L P1391 and P0340: Understanding CMP/CKP Sensor Issues and Diagnostics
Today I pulled diagnostic codes from a 1999 Dodge Ram 1500 with a 5.9L engine, and the only specific code returned was P1391 — Intermittent loss of Camshaft Position (CMP) or Crankshaft Position (CKP) sensor signal. I'm confirming whether CMP stands for Camshaft Position Sensor and CKP for Crankshaft Position Sensor, as these are critical components in engine timing. I also noticed a generic code P0340: 'Camshaft Position Sensor Circuit.' Given the similarity in symptoms and component involvement, I believe these two codes are likely related. My question is: Could this be pointing to a failing crankshaft position sensor? Or could it be an issue with the camshaft sensor or wiring harnesses? What's the most common root cause for P1391 on this model? Additionally, how should I approach diagnosing such issues without relying solely on generic online advice? Is there a recommended diagnostic method or flowchart system that works effectively for older vehicles like the 1999 Dodge Ram 1500?
I've seen this issue before on the 1999 Dodge Ram 1500 with the 5.9L engine — P1391 and P0340 often point to a failing crankshaft position sensor, especially when the symptoms are intermittent. It's important to note that aftermarket parts from jobbers can be unreliable; many fail quickly due to poor quality or design flaws. Always use OEM or dealer-grade components, particularly on this engine model where early versions of the distributor assembly and cam sensors had known reliability issues. I strongly recommend using a diagnostic system with built-in flowcharts and troubleshooting patterns before replacing any parts. Without understanding how the engine's sensor network works — including signal timing, reference points, and fault logic — you're essentially guessing. A highly recommended resource is d-tips.com, which provides detailed failure patterns for vehicles like this one. While it’s not free, the database is invaluable for diagnosing intermittent issues. The cost of such tools should be factored into your service pricing structure. If you haven’t included diagnostic tool costs in your business model, re-evaluate your operations to ensure profitability and technical accuracy. Using these resources helps avoid guesswork and reduces repair time and failure rates — especially on older vehicles where component degradation is common.