I have 2005 STI UK wide track Subaru.

The original headers went and needed replacing. And aftermarket set has been put on, but ever since I was getting the Check Engine Light with a P0031 code.

I purchased a new lamba sensor and fitted this into the first 02 sensor (the one on the headers as they all meet at the bottom of the car. This now shows a P0134 code.

There is a fitting that is plugged further up the headers where they connect to the bottom of the turbo and the headers I fitted were a up-pipe and headers in one.

I guess first question is do I need a lambda in the top hole ? do I perhaps have a bad lambda in the headers as it doesn't look like a genuine DENSO product.

OR can I have this mapped out of the standard ECU ???

Can see's to run fine.

Any idea's ?

 

This is the lambda I purchased.


http://www.ebay.co.uk/itm/121504808144

 

you should really only ever use genuine sensors when replacing, the ECU is calibrated to work with the original sensor and when you go aftermarket the scaling won't always be matched up. For example 3.80 mA on the stock sensor is 17.23 a/f ratio, but on your aftermarket one it could be 18 or 16 a/f ratio - there's just no easy way to know.

The sensor that goes in the uppipe is usually an EGT probe and you can have that mapped out OK - the primary sensor you need to have working so the car can properly hit closed loop fuel targets and try to give you some MPG when your not horsing it around.