2005 Mazda 6 2.3L Cranks but Won't Run: U0100 & P0330 Codes, No RPMs, No Spark - Possible Crankshaft Position Sensor or Ground Issue
My 2005 Mazda 6 2.3L with automatic transmission recently experienced a misfire, showing OBD-II trouble codes U0100 and memory code P0335 (along with P0300). I replaced the ignition coil, spark plugs, and wires, which improved the situation slightly—reducing the misfire—but the next morning, the engine cranks over but will not start. There is no spark and no RPMs. Freeze frame data shows normal values; all fuses are intact and relays are functioning properly. I noticed that the ignition coil connector was not fully seated, though it has power and ground connections. The question is: Could a faulty crankshaft position sensor cause the U0100 code to appear? Or could this be due to a wiring issue, poor grounding, or a problem with the Powertrain Control Module (PCM)? I'm seeking clarity on whether the crankshaft position sensor is the root cause or if there's another underlying electrical or mechanical factor.
The U0100 and P0335 codes are likely separate issues. U0100 typically indicates a communication failure between the vehicle’s modules, while P0335 points to a faulty crankshaft position sensor or related wiring. For detailed troubleshooting steps on P0335 in your 2005 Mazda 6, refer to this forum thread for specific causes and solutions.