Treat P1684 as informational only: it means PCM memory was recently cleared and does not indicate a fault. For P0340 (no cam signal at the PCM during cranking), inspect the camshaft position sensor, target magnet, sensor ground, signal circuit, and 8-volt supply for opens, shorts, stray signals, or intermittent wiring before considering a defective PCM.
The owner of a 2000 Dodge Neon asked what trouble codes 1684 and 0340 mean. An expert explained that P1684 only means the computer memory was recently cleared and is not a problem. P0340 means no camshaft position sensor signal is present at the PCM during cranking, with possible causes including a defective CMP sensor or target magnet, open or shorted signal or ground circuits, an 8-volt supply fault, intermittent wiring, or a defective PCM. Another user noted that clearing the code requires checking those items.
