Apologies for bringing up the subject again.

I've been told there are 2 lambda sensors on my 04-05 JDM STI blobeye.
Rear (presume in downpipe) and front (in manifold).

I've only ever replaced the downpipe one on my '99 UK car.

Do I need 2 ? Or are these just alternate locations ?

 

Front lambda sensor is read by the ECU for purposes of fuelling / timing and is critical in the running of the car.

The rear lambda sensor measures catalytic converter efficiency and although the ECU reads from it, nothing happens if it detects a problem (OR IS MISSING) apart from throwing CEL P0420. The running of the car is unaffected.

Corradoboy posted a good diagram on here a couple of days ago


Shaun

 

Link to the pic on t'internet

http://i70.photobucket.com/albums/i9...st-diagram.gif

Shaun

 

many thanks !

 

Mostly true, as the front sensor is wideband, the rear sensor (2 point) is much more accurate at defining Lambda 1 so is used to trim the fueling and also to control a function for 'de-oxygenating' the catalyst after fuel cut events. So if that sensor is removed or U/S then you'll loose those as well as the catalyst efficient check.

Simon