Got a P0420 code

cavaddict

Hmmm, as above really. If i reset it, it comes back on about every 300 miles. Am thinking either a sensor or the cat is on its way. Any ideas guys?

pottsey

i get the same on mine used to come up with the previous cat which was new ,also comes on with my sports cat so im guessing the sensor is goosed

JohnnyN

I used to have this too on my old sport cat but not since my new one fitted 2 years ago. Sensors were fine. There have been reports from other members with this problem.

A blowing flexi has been mentioned. Type in P0420 into the search bar at the top R/H corner of the page to see other threads covering the same problem.

cavaddict

Righty, will try a process of emilination then. Got a spare Vectra here so will try and get to the bottom once and for all my changing one bit at a time until i get it sorted. Do you think i should start with the first lambda? notsure.gif

vocky

P0420 Catalyst System Low Efficiency

so either the cat is duff or the lambda after the cat is duff dunno..

MikeS

easiest way is to get real time display of rear lambda pulsing

the p0420 is not saying the rear lambda is faulty, it saying the cat is not doing its job

it can be caused by many things including a possible lambda problem

i have seen the front lambdas not pulsing correctly and throwing out p0420 codes

cavaddict

What i guess i'm asking, is, where's the best place to start. Got another car here to take bits off of, but it's all time, so would rather start with the most likely cause as the fault only comes on every 300 miles.

MikeS

then replace both lambdas and the cat 🙂

it is all one piece in theory

the p0420 code does little imo

it is just a nag

it does not adjust fueling

cavaddict

Thing is that i could do with knowing which bit is at fault as at some point in time the 'spare' car will be up for sale and i'll still have to find the fault. Is there any more likely part which may be at fault?