Yaris With P0420 Warning

[StephenH]

Driving back home tonight the engine warning light came on. I checked the code when I got home and it was P0420 which I gather is 'Catalyst Efficiency Below Threshold (Bank 1)'

Any suggestions on what to check? A quick google throws up all sort of possibilities.

I don't know if it is relevant but nearly 2 weeks ago I had a new exhaust manifold fitted as the old one had cracked. Might it be either debris from this in the system or the sensor having been damaged or dislodged? Is it worth taking the car back to the garage that did the work for them to check?

Also, is the car OK to drive for a while before getting this seen to? I've not really got a good opportunity to get it looked at unless I have to - I've got an interview tomorrow and am away next weekend.

It's a 2000W 1.0 for reference.

[Madasafish]

answered on hj

[Chris81]

It is almost certainly linked to you getting the exhaust manifold replaced. The exact same code came on on my friends Yaris after the cat was replaced, most probably due to the different tolerances in the aftermarket cat.

P0420 means that the reading take from oxy sensor 2 (after the cat) is too close to the reading taken at oxy sensor 1 (before the cat). This happenned about 2 years ago to my friends car and the P0420 has been on since with no negative effects. Car has passed 2 MOTs no problem.

I'd take your car back to the garage to make sure the new manifold is all sealed up ok, and if so then I wouldnt worry about the code. It may be a bad/damaged sensor, it may be the cat, it may be the sensors don't like the new exhaust manifold but on a 12 year old car do you want to spend hundreds trying to fix a fault code which isn't affecting how the car drives or the emissions.

[Parts-King]

Car has passed 2 MOTs no problem.

I'd take your car back to the garage to make sure the new manifold is all sealed up ok, and if so then I wouldnt worry about the code.

It might not be a worry now but next year it WILL fail the MOT for an engine warning light on, get it sorted out now whilst you have the chance

Kingo

[StephenH]

It won't fail the MOT for engine light on if I use my code reader to clear the fault before taking the car to the garage... ;)

Thanks all, I'll see what the garage says. Hopefully they'll run an emissions test - they do MOTs as well as repairs - so we can at least find out if it is actually a worry.

[Madasafish]

It won't fail the MOT for engine light on if I use my code reader to clear the fault before taking the car to the garage... ;)

Thanks all, I'll see what the garage says. Hopefully they'll run an emissions test - they do MOTs as well as repairs - so we can at least find out if it is actually a worry.

I did that on son's and eventually the light just came on again after about 0.5miles.. So with prolonged idling at MOT station, it is likely to come on again.

Chances are you have a minute hole along the welds in the cat - this can be fixed by exhaust paste but in time pollutes the catalyst and you get a prolonged and permanent failure...

[Chris81]

Car has passed 2 MOTs no problem.

I'd take your car back to the garage to make sure the new manifold is all sealed up ok, and if so then I wouldnt worry about the code.

It might not be a worry now but next year it WILL fail the MOT for an engine warning light on, get it sorted out now whilst you have the chance

Kingo

As far as I'm aware this is incorrect advice. The new MOT rules will check for warning lights relating to SAFETY e.g. airbag lights, stability lights, traction lights, electronic handbrake lights but NOT the engine management lights.

http://www.theaa.com/motoring_advice/car-servicing-repair/mot-changes-2012.html

[Parts-King]

Well its not as simple as that in reality

An engine management light could come on for a number of reasons, for something as simple as a sensor which gives a high CO or HC reading, it could be that somebody has removed the factory catalytic convertor and that has nothing to do with safety but will fail the MOT

What I am saying is you don't want to be presenting your car for MOT with any warning light on, it will most likely (next year now) to fail the MOT

Kingo

[Chris81]

The bottom line is if your engine management light is on, this in itself is NOT a reason for MOT failure. It is wrong to state that this light being on will result in a fail.

Airbag, traction, vehicle stability etc warning lights are a different story. I'm glad VOSA have made the distinction and not just had a blanket fail on all warning lights. There will be tens of thousands of cars going round with the engine management light on which are perfectly safe and well within emissions requirements.

[Madasafish]

The bottom line is if your engine management light is on, this in itself is NOT a reason for MOT failure. It is wrong to state that this light being on will result in a fail.

Airbag, traction, vehicle stability etc warning lights are a different story. I'm glad VOSA have made the distinction and not just had a blanket fail on all warning lights. There will be tens of thousands of cars going round with the engine management light on which are perfectly safe and well within emissions requirements.

NOT if the warning is for a catalyst failure - which is what this is..

[Chris81]

What you're failing to understand is the light itself is NOT a reason for failure. How many times do I have to say it!?

And just because the P0420 light is on, does not necessarily mean the catalyst has failed or the car will fail its emissions. It could mean a sensor is duff, or it could be that the readings are outside the tolerance set by Toyotas ECU but are still within the legal limit. My friend's old 1.0 Yaris has had the P0420 code and engine management light on for over 2 years. The car drives fine, passes emissions fine, and has not received an advisory for the EML being on.

The OP has a 12 year old car. If it passes an MOT is it worth throwing money at it replacing parts that don't need to be replaced, solely to try and get rid of the P0420 code.

[Parts-King]

What you're failing to understand is the light itself is NOT a reason for failure. How many times do I have to say it!?

Ooooh knickers twisted?

You are correct for this year but NEXT YEAR might be a different story, the MOT regs have still not been finalised (well I think they were then changed, then put on hold then changed again) but it is most likely that a permanantly ON engine warning light will fail EVEN IF the emissions pass. Presenting a car with any warning light on NEXT YEAR will be a different story to this year

Kingo

[Chris81]

I'm not wanting to be argumentative, I just don't want people worrying unnecessarily.

The changes on MILs were due to come in on April 1st this year. This still didn't include the engine management MIL, just the MILs for airbags, electric power steering, electric handbrake and the like. However, these changes did not get fully implemented. Instead they were flagged as Advisories only, so if you took a car for an MOT with the airbag MIL on after April 1st 2012 then you'll have got an advisory. If you take it in next year when (or 'if') the new regulations come in, then it will be an MOT fail. But it still won't cover the EML MIL - presumably as VOSA know that there are hundreds of problems this could refer to. If it's a problem that they're concerned about, such as emissions, then this will of course be tested when they do the emissions test. The MOT doesn't care if you have the EML MIL on for things like throttle position sensor or air flow malfunction.