The crankshaft position sensor is a sensor that monitors the rotational speed and position of the crankshaft. It sends data to the ECU to make necessary adjustments when any kind of malfunction occurs. Bad wiring harness or loose wiring can cause the signal of the crankshaft to be cut off while AUDI A4’s engine is in operational mode. You will notice acceleration issues, reduced gas mileage, rough idling- once after the CPS becomes faulty. Replacement is the most effective solution I guess. Still, prior to replacing the sensor, you should consult a reputable AUDI mechanic and run some tests – for getting a confirmation that the faulty source is the CPS.