Where abouts is the spark plugs on the 2004 bmw 520i

Fuse Box Diagram BMW 5-Series (E60/E61; 2003-2010)

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Here you will find fuse box diagrams of BMW 5-Series 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 (520i, 520d, 523i, 525i, 525d, 528i, 530i, 530d, 535i, ...

I would have swapped coils first. If the code goes for one to the other, it is the coil. If it stays the same, change that plug and or wire/boot. Next check the wiring . Breaks mostly close the the coil plug. Then head towards the injector.

Do you mean petrol is leaking from the spark plug area?

1. if automatic, try to shift gear to drive then back to park then try to start again. do it twice , if still wont start
2. check battery terminals if lose or with white substance pour clean water until substance is dissolve. then start.
3. check battery
4.

CHECK FUSES

Never rule out sensors, based on the fact they sometimes
work or you have spark

You need an oscilloscope and look for milli second
misses and spikes

Use the scope on everything,fuel pump etc

the exhaust-gas alarm lights on. what should I do?

is it getting spark or fuel

[url=http://safemanuals.com/user-guide-instructions-owner-manual/BMW/520I-_E]This[/url] is the closest thing I can find.
If that isn't it, you should be able to find it on Safemanuals.com.

i would check the fuse for the fuel pump and the relay.