I have replaced the crankshaft sensor 3 times in 2 week for the same check engin

did you use a Nissan part? may be an inferior part or you may have a wiring issue to the sensor, may need to take vehicle to a certified Repairpal shop for proper diagnosis

**HANDS-ON** TESTING will be required to determine what the exact failure is .. Trouble codes are merely a guide to begin diagnostic troubleshooting - codes do not indicate a particular part has failed.