P0420 after New cat, help please.

[Col748]

Right here goes if anyone could help with this one it would be great.

I have a 2002 yaris and the engine light came on about a month ago it was a downstream exhaust sensor heater fault, the heater circuit was open circuit in the sensor so the sensor was at fault. I replaced the downstream sensor and while I was at it I replaced the upstream sensor and the cat as well as the cat was rusting away and the hangers had rusted away to the point of snapping off. I replaced the upstream sensor as by time I'd got it out I guessed it would probably fail in a week or two anyway.

So a day after fitting the two sensors and the cat and clearing the codes the light came back on. I had a new code p0420 cat efficiency fault. Long storey short I messed about swapping old sensors about, checking for leaks, eventually putting the old cat back on with the new sensors and the light stays off.

So with the old cat and new sensors I do not get a cat code p0420.

I spoke to the supplier and they have had a concern with Japanese built yaris and new cats bringing this code on, spoke to another supplier and they have a similar concern with Japanese built yaris which this car is.

So has anyone else had this problem, how did you get round it?

I don't want to blank out the light or buy an original cat as it's £1200 just for the part.

Thanks Colin.

[malibuguy]

you have to put on a proper OBD2 converter on there & most likely a "heavy loaded" one at that.

I am damn near willing to bet money the replacement converter that was installed was a replacement for an older vehicle
I see it ALL the time, shops will put on cheaper, incorrect converters & charge top dollar as if it was proper replacement

if you want to bandaid it...use a drilled out spark plug defouler to space out the downstream O2 sensor to fool it into thinking theres more cat on there.

or install the proper converter

[CoryM]

Just to add to what was (correctly) said: The OE cats are designed to last for at least 7yrs for emissions warranty. The cheap aftermarket ones are designed to barely pass the OBD requirements since the material is expensive. I'd say 1-2yrs is the typical life for the cheapest cats and, as you have found, sometimes they just aren't good enough. There are decent aftermarket cats out there, but not sure for the Yaris.

[malibuguy]

All aftermarket cats that i know of are made of 409ss for the shell, same as OE. Some may use aluminized steel for the outer heatshield (like Catco, AP, Eastern) and some will also use aluminized steel necks as well (Dynomax).

The real money is whats inside.

I personally run a 100cell, metal core race cat with a spacer on the O2 sensor. Its still cleaner then a VW, lol

[Col748]

That for the replys chaps.

Looks like I may struggle find a good cheap cat, maybe I'll try one of those spacers. I've never heard of those spacer things until now.

[malibuguy]

Vibrant makes a nice proper one, and a tunable one as well

[ncp13]

Hello

As per the repair manual

DTC P0420 is detected when the vehicle is driven at an average vehicle speed of approximately 50 km/h (31 mph) with a city driving pattern for approximately 30 minutes, and then driven for approximately 15 minutes at a constant vehicle speed of between 70 km/h and 90 km/h (43 mph and 56 mph) with the transmission gear selector lever in the 5th position. (If the engine speed remains 1900 to 3400 rpm and the engine load remains 25 to 50 % after the catalyst is warmed up for 60 seconds or more, the detection for DTC P0420 will be performed)

I havent seen a bad (new) cat but check for a bad (new) sensor B1S1 and B1S2. Pins ok in the plugs ? Maybe loose?

I can post the proccedure if you want but you will a Toyota THS2 or similar to increase or decrease injection volume so you can check the response from the sensors .