My Sti 7 has two lambda (O2) sensors. 1 in the headers before the up pipe & another to the rear of the down pipe.

What is the reason ?? So that it can be more precise on Mixture Control ??

Thanks

Dean

 

Sure regulations stated that new cars after certain date needed a pre cat and post cat one for emissions. Could be wrong though.

 

Dean

AFAIK one is the "real" lambda sensor to feedback to the ECU on open loop to get a stoichimetric fuel / air mix and the other in the dowpipe is an 02 sensor to see how well the catalytic converter is performing !!

The ECU looks at the one in the down pipe and gives a CEL P0420 if it thinks it's not there as it thinks the catalytic converter is not working!!

Shaun