P0335

What the code means

P0335 flags a fault in the crankshaft position sensor (CKP) circuit. The sensor reads crankshaft speed and position, and the ECM uses that signal to control ignition timing and fuel injection. Without a reliable signal, the control module doesn't know when to fire the spark and deliver fuel.

The code sets when the sensor signal is missing or unreliable during cranking by the starter motor. Causes are both electrical and mechanical: an open or short in the sensor circuit, a poor contact in the connector, a failed sensor, a damaged signal plate on the crankshaft, a weak battery, or a faulty starter motor — the last two distort the signal through low cranking speed and voltage drops.

Symptoms

• Check Engine light is on;
• lack of power or power loss while driving;
• the engine stalls, and starting problems are possible.

Diagnosis and repair

1. Check battery voltage and starter motor operation: a weak battery or a dragging starter motor produces an unreliable signal during cranking and is often the root cause of the code.

1. Inspect the CKP sensor wiring and connector for damaged insulation and corroded contacts. A bad connection is a common cause and can be fixed without replacing the sensor.

1. Measure the sensor winding resistance with a multimeter. Typical value is 500–1200 ohms. A significant deviation means the sensor has failed.

1. Replace the sensor once the fault is confirmed. The BMW part number is 12141703276.

1. Check the signal plate on the crankshaft: bent or missing teeth give an unreliable signal even with a good sensor.

A common diagnostic mistake is replacing the sensor right away without checking the circuit, battery, and starter motor: the code points to the whole circuit, not just the sensor itself.

Secondary problems

• the engine may fail to start or stall suddenly while driving — that creates an accident risk;
• long cranking by the starter motor during start attempts drains the battery and accelerates starter motor wear;
• in some cases, misfires caused by the fault damage the catalytic converter. Don't put off diagnosis: the fault affects basic engine functions and can show up at the worst possible moment.