Yaris P0420 code

[ph9]

I have a Mk1 (2001) 1 litre Yaris. If I clear the MIL by disconnecting the battery it stays off for a good few miles then comes back on again.

I've bought a code reader, and it's displaying "P0420 Catalyst system efficiency below threshold bank 1".

On another screen it had status indicators for different components, and from memory I think it said that Oxygen Sensors were OK.

Is the problem likely to be the catalytic convertor or exhaust, and if so, how much will it cost to sort? I've read that some third party cats don't work for long, so perhaps I'd need a genuine Toyota one, which I imagine won't be cheap!

Someone had a nosey in the engine by the other day, and they said that my engine was an earlier one because the exhaust manifold came straight out of the engine block at the front (or something like that!) I'm not sure what the later ones are like - perhaps they have a cover over them or something!

[Bdevo3]

Earlier one crack the welds on the underside of the exhaust manifold around the welds it gives a false oxygen sensor reading

[helix402]

Check exhaust emissions. If they are ok for the mot ignore the light.

[ph9]

Thanks very much, I'll try to check the manifold - is it easy to tell if there's a crack in it?

It passed its MOT last week, although I did clear the MIL beforehand.

I suppose the problem with ignoring the problem is that the MIL light is on constantly, and may be indicating another more serious fault which I wouldn't be aware of.

[E-bmw]

Check engine light won't result in a failure if the readings taken by the tester are within limits IIRC.

[helix402]

Petrol Toyotas of that era are renowned for spurious cat efficiency codes. Toyota’s official remedy is: new cat, lambda probes and software update. Hence my advice. Or you could buy a lamdba sensor spacer and put it post cat if the light annoys you.

[ph9]

Thanks!

It sounds like the official Toyota solution would cost many times what the car is worth! I'm going to take it to a good mechanic I know, and see what he thinks of the car and the few problems it has. I'd not heard of a Lamda sensor spacer before, so that's good to know.

[andyf1140]

Had the same problem on my sons car and it ran fine, we just kept checking the code and clearing it periodically. Eventually we had to scrap it because it had other faults that made it not viable to repair.