Can't fix P0420 error code for Toyota corolla 2005 model. Please help!

Question

HI,

I have Replaced both O2 sensors then malfunction indicator light went off but after driving around 70 to 100 miles lights went on again.

So i was going through forum and find out  that may be i need to replace Spark plugs, Clean throttle body, Head Gasket, Solenoid and charcoal filter, PVC valve.

what is solenoid and charcoal filter and how to clean throttle body


could please suggest something that what should be replace??????

Thanks in Advance...

Answer 1

P0420 Catalyst below threshold 

Thus all depends on what the cause for the catalytic to go below its threshold, The catalytic convertor is capable of going well over 300,000 miles provided that the engine and the transmission maintanance are kept up, The OBD II system was design to maintain fuel control so the catalytic convertor can perfrom its job in keeping harmful emission emitted into the atmoshpere. If you have a scan tool that can read data , with a good working front 02 sensor the rear 02 sensor should read above 650 mlvts.  below that value and its stays below that value for a period of time you need a catalytic convertor.

  This here is a faulty catalytic convertor, this value stay below its threshold, the history of this Toyota was it had a P0171 lean code condition that has left neglected for over a year, until its emission test was required. Not knowing that P0171 was recalled by Toyota for a intake gasket and a new front 02 sensor. as a result a  non functional catalytic convertor