Avensis 2.0 Vvti Oxygen Sensors And Cat

[Normanc Cook]

Hi all,

This is my first post on this fantastic forum, so bear with me!!

I recently bought a '04 Avensis Tourer 2.0VVTi and have to say am really impressed with it. Having come from a Mondy TDCI it took a while to get used to the lack of torque...

I have been having issues with P0420 (Catalyst System Efficiency Below Threshold Bank 1) and P0430 (Catalyst System Efficiency Below Threshold Bank 2) fault codes. I had to replace one of the pre-cat lambda sensors as the heater had failed. Ever since, I have been getting the codes mentioned. (I have Torque on my Android phone with a bluetooth OBDII adapter. Awesome bit of kit.)

However, I can drive for hours / hundreds of miles and not get the fault codes. Then on other days, the MIL comes on and sure enough, P0420 and/or P0430. (Basically the same fault for both cats in the exhaust manifold.)

My question: Are the cats likely to be dead or does my car need the software update I have read about that widens the parameters for the post cat sensors? If it is the parameters, can resistors be fitted in line from the sensors to "mechanically" introduce a wider set of parameters?