please help me with my 2002 b5 s4. out of nowhere it wont start. crank and cranks, no start tho. the fuel pump relay and fuel pump are good, but what sends the switched ground signal to fuel pump relay to turn it on??? there is constant power going to all the prongs on relay, but the actual one that is switched to engage relay which is a ground, is getting its signal????? and no power to fuel pump fuse. i jumped relay and it engaged fuel pump, but wont do it without me jumping that relay. does the ignition or ecm or what send the switched signal to that relay?? please help so i dont have to take it to the stealership. and by the way i did check for CEL lights and isnt showing any codes. thanx in advance!!!

Try the crank sensor that is kind of what was going on with me, but mine would turn on eventually. It would crank very healthy but no fuel to the engine and yes i still had power to the prongs like you. I tried everything, and sure enough it was the damn crank sensor it only cost 63 off ebay and is very easy to install you should look at some of my other posts on the crank sensor issue. It cured my problem which was getting worse and one day just would not let my car start at all. Here is what happend to me, Id start the car no problems then drive around and do errands park for 10 mins and go to turn it on and crank crank crank no fire up so i would sit there in a parking lot for at least 10 more mins and boom it would fire up. It did this to me intermittenly but eventually got to the point of no start for a whole day then i gave up and changed the crank sensor and it really cured the problem. Hope this helps you.

there a way to test that sensor? will vag cable show a code if i buy that cable and hook it up or will it not notice that sensor being bad?

and if a vag cable is what i need to get to find the problem, can u recommend a decent one off ebay that works?? thanks

Not sure about the vag thing. But I mean you could take the sensor off and clean the tip of it sometimes it will get dirty and see if it helps but if it turns on and still gives issues but the cleaning kind of helped you then just buy a new sensor. That is just what i would check if i were you because my car had me running all over trying to figure out why my fuel pump would not turn on sometimes. remember it is only 63 dollars for a new crank senor. I think that is your problem from what ur telling me. My car did not give me a check engine light when i was having my issues so there wasn't a way for myself to test it.

so where is this sensor located?? and whats easiest way to get it off??? my fuel pump relay isnt getting a signal from the ecu to engage the fuel pump. does that mean the ecu is bad or does that sensor ur talking about tell the ecu not to pump fuel if it goes bad?? thanks for help!!

under the coolant tank deep down in there its tight. its on top of flywheel housing, under the coolant tube with the sensor on it (driver side) all you need is a 10mm wrench and you can get to it from top of engine. easy to install no wd40 needed.