So yesterday my 1998 a6 2.5tdi v6 started littleknock, When driving faster the engine like "yelled" (no fault codes) Today morning the engine was knocking very strongly. I HAD to drive it to work (5km). After work I started the car and the knocking was very bad. I went to some car shop and bought RVS D6, new oil filter and new oil. Went to home and changed oil. After the oil change the car did not want to start. The knocking sound is like someone hits engine with metal pipe. It does not sound like valve knocking, its very strong, engine runs very badly and the whole engine shakes. After the oil change it started blinking that "glow" light. I stopped the car and checked with vcds whats wrong. It showed me this: Address 01: Engine Controller: 4B0 907 401 P2u Component: 2.5l/4VT EDC G200AG D60 Coding: 01001 Shop #: WSC 00012 2 Faults Found: 01126 - Engine Speed Signal 16-10 - Signal Outside Specifications - Intermittent 00513 - Shareware Version. To Decode all DTCs 27-00 - Please Regi Master/Activate Readiness: N/A I checked the engine speed sensor and cleaned it. Now there is no fault codes. And engine is not starting. I did not remove any wires or anything. I checked every wire, everything seems to be fine. When I try to start car, someone starts hitting my car with that metal pipe again. It does not even try to start. I know the 2.5 tdi v6 is very bad engine but I love the car, its very good like outside. Thers no rust and I keep very good care of it. Also I know also how to fix almost everything about the car, but not engine. And this audi is my first german car so I dont know its engine yet, I have no idea what I do now or what I do next. Also sorry for bad english.