Yaris engine code P0420

cbrpaul

My 1.0 litre 05 yaris has the above code , which is

Catalyst Converter Below Efficiency Threshold ( Bank 1 )

Looking at the past years or 2 MOT`s it has failed MOT`s on

Excessive Co2 on idle !!!

Dealt with by using a fuel cleaner and a rant around the block I beleive and passed and by Toyota by replacing the air filter and cleaning the PVC

Looking into the code it seems it could almost be anything , from lamba to Cat to Maf

So has anyone had similar issues ? and solved it ?

Any help or advice greatly appreciated

Thx

forgotmyname

When did it have a proper service? Plugs, Leads fuel filter etc?

Lots of things to check. 1st thing is it running properly? No misfires because of the plugs/leads or coil(s)?

Faulty lambda sensor? CAT itself faulty?

You need a proper mechanic who look at the code and doesnt jump to conclusions and say you need a new CAT.

What can cause that code. Fuelling issues, Timing, Ignition...etc etc..

jcb208

Most likely Cat had the same problem on a Vauxhall new cat then passed emmisions easy and no more p0420 fault

cbrpaul

many thx for the replies , I have it booked into a local non dealer garage for a full diagnostics , where they will also check the lambda and cat !!

fingers crossed its a £50 lambda and not a £200 cat + fitting !!!

sgun

"dealt with fuel cleaner and a rant around the block" Get fuel emissions read. Burn it up and down a fast road for about 30 minutes, REALLY over rev until it feels painful (don't speed though!) Get checked again immediately. If readings are then down its most likely the cat.

If a cat is bad you can hide it for a while but it will always come back to bite you.

cbrpaul

will the diagnostic tests prove its the cat or not ??

sgun

No, it will give you the code that you already have most likely. You can't check the cat as the parts that work are inside. If there is an obvious crack or decay to the outside then there is an obvious problem but they are incredibly hardy on the outside. You can do some checks to the sensors as there is one going in and one going out ( or four, depends) and they can read the up and down lambda readings. However this will not tell you if it is the cat or not.

The catalytic convertor makes fuel "clean" to fulfill EU emissions levels. You can run a car without a cat no worries but it would be illegal. The sensors check the levels. Therefore if a sensor is faulty it might imply the cat is at fault. On a Micra I assume a sensor should only cost about £40 all in fitted but you might find the code coming back in anything up to a year. In which case you know its the cat. Can you give the exact readings from the last MOT? That will give a clue...

forgotmyname

If they are a decent garage they can compare the signal from the lambda sensors to see if they are within range and operating properly.

Lecture on testing them properly will put most people to sleep before its halfway in.

cbrpaul

I only have a pass readout for MOT emissions

it states natural idle test CO limits <= 0.300% actual 0.003%

it also states at fast idle 3000rpm
Lambda limits 0.970-1.030 actual 1.006

Also at fast idle CO limits <= 0.200% actual 0.002%
HC limits <= 200ppm actual 30ppm


Any use ?

colino

Have a good google for P0420. As I've said many times it is an easy way for a dodgy garage to rack up huge bills fixing and it could be anything from a cat on its way out, poor servicing, to a pinprick hole in the exhaust system. The fact that an Italian tune up got your car through an MOT tells you the cat was fine (no snake oil fixes poisoned cats) and the car has to be gone through methodically (after a good service) to find the fault.

forgotmyname

Italian tuneup works wonders if the cars used for mainly short journeys or lots of sitting in heavy traffic.

Good stretch of dual carriageway, Stick it in 2nd or 3rd. Keep the revs between 2000 and 4500rpm.
Accelerate fairly hard then keep it around 4500 for 20 - 30 seconds and slow down to 2000 rpm. Then repeat a few times.

Depending on where the red line is on your rev counter you may want to go upto 5000 or 5500.

Keep it 500rpm below the red and as long as the engines in good condition it wont suffer.

Dont do this with a neglected engine though.