No boost

[arranstone]

Took my S2 out tonight for the first time in about 6 weeks, it last ran perfectly.

For some strange reason I now have very little boost. My gauge is showing about 0.5 bar. Had vagcom in the car while i was out and read the codes there were 4 i think. So cleared them, drove off and had full boost in second gear, changed to third no boost.

Checked the codes again when i got home, they are;
00540 knock sensor
00513 engine speed sensor

Have checked the MAF sensor connector/plug and the WGFV connectors all fine.

Anyone have any ideas?

[k.alle]

I think (not sure) knock will reduce boost.
Had something similar happen after rebuilding my engine which I solved with cleaning the knock sensor connectors behind the engine.
Might be worth a try.

[andyg plym]

I’ve had a knock sensor failure before it cuts boost, can come back when switched off and back on. They are a bit akward to get to

[arranstone]

Found the problem.

[arranstone]

Wheres the best place to get a
new one?

[andyg plym]

That autodoc seems to do a few

[arranstone]

Thanks Andy will have a look there now.

[Monkeymagic]

Bought both of mine recently from bosch

[Greg_S]

Yeah be careful with autodoc, i know other members have had some issues with orders. Bosch dealers should be able to help you though

[arranstone]

Got a new knock sensor from motorparts direct in the end for £38. Fitted it and problem solved. Back on boost