Audi 2.7t speed sensor replacement (S4, A6, Allroad)

This is a very common and unpredictable issue faced with Audis and VWs where your car has been running fine, but when you turn it off and try turning it on it cranks and cranks...but doesn't fire up.

The problem could be anything, but a really common issue with the 2.7t and 1.8t engines is of a bad crankshaft speed sensor. Its a hallmark sensor meaning that even if its a little bad it will not operate at all and thus will prevent your car from turning on.

Your check engine light may also come on but not necessarily, when my audi allroad faced this issue it was driving fine only showing me the symptom of a rough idle and one day it suddenly would only crank and not start but the check engine light remained off. After the crankshaft sensor replacement it started up fine.