Summary
P0340 means the PCM is not detecting a valid signal from the camshaft position sensor (CMP). The most common causes are a failed CMP sensor (45%), damaged wiring or connector (25%), and a damaged reluctor wheel or tone ring (10%). This code can cause no-start conditions or unexpected stalling, making it a priority to diagnose. The sensor itself is usually inexpensive and accessible.
Severity: High — engine may not start or may stall unexpectedly
Safe to drive: No — stalling risk makes driving unsafe; may not start at all
Repair cost: $20–$300 depending on cause
DIY difficulty: Easy to Moderate
What does P0340 mean?
The camshaft position sensor (CMP) tells the PCM where the camshaft is in its rotation cycle. This information is critical for determining ignition timing and fuel injector sequencing. The sensor reads a reluctor ring (tone ring) attached to the camshaft and generates a signal that the PCM uses to synchronize spark and fuel delivery with each cylinder's position.
P0340 is set when the PCM does not receive any signal from the CMP sensor, or the signal is so corrupted that it cannot be interpreted. This is different from P0341 (range/performance), which means a signal exists but is not within expected parameters.
Without a valid CMP signal, the behavior depends on the vehicle. Some engines will not start at all because the PCM cannot determine which cylinder is on its compression stroke. Others will fall back to using only the crankshaft position sensor, allowing the engine to run but in a degraded "waste spark" mode with sequential injection disabled. In either case, the engine may stall unexpectedly.