No Rear O2 Sensor on my S40?

[toddmardent]

I have a May 2000 S40 built in the Netherlands. Distributed in Australia.

There is only one O2 sensor present on the vehicle and there does not appear to be anywhere to install a rear sensor?

Does anyone know if this this common in Australian distributed vehicles

[madspeed50]

Do they come with a catalytic converter? Usually the rear is just to measure the effectiveness of the cat Useless other than that

Sent from my rooted, rommed Galaxy Nexus....

[toddmardent]

yes there is a cat. thought something similar. so basically its the front that sorts it out and the rear is just measuring?

[regent]

That's right, the 'upstream' O2 sensor tells the computer how to solve the air-to-fuel ratio (or the mixture equation), the 'downstream' sensor plays no part in that if all is well. It is there to monitor the Cat's efficiency only. If the upstream sensor fails, then the downstream sensor may take over to maintain AFR.

[jimmy57]

The up one on x40's will be right behind turbo and the rear is stuck into the catalyst that is just under turbo. But some versions in some markets may not have the rear even into the early 2000's.

The rear sensor does have function for fuel trim. Rear O2 sensors were added to comply with catalysts diagnostics rules but since it is there the engineers decided to employ it to also correct fuel trim. The front can oscillate rich-lean but that effectively just keeps the fuel trim between the white lines. Using the rear, after the primary catalyst, allows the fuel trim to be adjusted to keep it centered between the white lines (highway lane analogy). The catalysts last longer if the fuel trim is corrected to a smaller tolerance. That means less warranty costs during the long emissions hardware warranty, especially the states with catalysts covered past 100K miles.