Aftermarket O2 Sensors? 2002 Volvo S80 T6

bronson1111 · Post by **bronson1111** » 10 Jun 2011, 08:20

So I don't know much about cars, but I am learning! I noticed that my T6 has two O2 sensors in the front and two on the catalytic converter. My CEL light is on and I am getting a PO420 code (Catalyst system efficiency below threshold (bank 1)) and I want to fix it!

Now my main question is.. do I need to replace all of my O2 sensors? I hope not.. they are quite expensive. Also, should I buy a cheaper after market brand? Let me know what you think!

Thanks!

Post by **boosted5cyl** » 10 Jun 2011, 11:06

That code is for the sensor after the cat, on the passenger side. If you fllow the "transmission tunnel" from the motor back, you will see the sensor on the to of the exhaust pipe. Assuming your car is LHD that is!
Your car has two fuel banks one covers cyls 1-3 and the second covers 4-6. Each bank has two O2's and one cat. The ones nearest the motor (AKA upstream or pre-cat O2s) are used to monitor the A/F mixture and make on the fly fueling and ignition timing adjustments, amongst other things. The other two sensors (AKA downstream or post cat O2s) are there only to monitor cat efficiency, they have no bearing on the performance of the vehicle.

Hope this helps.