Oxygen Sensors/Cat

Horizon81

Anyone technical, I'd really appreciate your advice.

My friend is having realy bother with a P0420 fault code coming up. The car is a 1.0 Yaris, mark 1. The fault code means 'catalyst system effciiency below threshold'

Now I'm no mechanic but it basically means that the engine is running lean. The car's 7 years old and the garage spotted a big hole in the exhaust prior to the cat so their first port of call was to fit a new cat. Job done (not genuine Toyota but a decent pattern part), engine management light stayed out for about 4 months. Then it came on again, same fault code. Garage turned it off and a month later it came on again. It's now on all the time.

Took it to a different garage for second opinion who say it could either be a dodgy cat or the sensors need to be replaced. Cost of changing the sensors for genuine OEM ones is about £250 but the garage says there's no guarantee of fixing the problem. I haven't driven it yet but the car apparently still runs ok, and as it's running lean I expect it to pass emissions test ok. The second garage say that if we just leave it, the engine could overheat, melt spark plugs, pistons etc.... Is this true? Could an engine running lean lead to that? I can just imagine them spending £250 on new sensors and the problem still being there...

Clark80

Similar issue about 5 years ago although I can't remember the fault code. We had to change the Lambda sensors I think

Lum

Are they saying it's the O2 sensor before the cat that is playing up, or the one after it?

The one before the cat is used to actually adjust the engine mixture and thus can lead to lean/rich problems. The one after the cat is used purely for monitoring and throwing up fault codes. More often the fault is with the bloody sensor rather than an actual fault.

I wouldn't bother with genuine OEM ones for £250. Just get an NTK one for £50. Chances are being a Toyota they use NTK lambda sensors anyway.

Changing an O2 sensor is not much harder than changing a spark plug, only you have to crawl under the car to do it and use a special tool (costs a tenner). If a garage is charging you more than an hours labour then they are ripping you off, unless the Yaris puts them in a stupid place.

Front O2 sensor. Rear O2 sensor. Both £51.02

Note that if your car has VVTi you'll need different ones.


Edit: Just realised they sold you a new cat rather than just welding up the hole. Bet that was expensive!

TiTheRev

Why not just take it to Toyota and get it diagnosed properly???

Most dealers do a fixed fee diagnosis, and if they can sort the problem within the alloted hour (for example) then you walk away with a cheap fix. If the diagnosis shows something else, like the cat or lambda, then you can thank them and take it to your fred in a shed to be fixed with cheap as chips parts more confident that the problem will be fixed. You never know, Toyota may be competitive

I really cannot understand the prejudice and stereotyping that goes on about dealers. Why are all 'independants' not branded cowboys like Watchdog et al might suggest?? There is good and bad in all trades, but at least if you get the diagnosis done at Toyota they will be able to trace the fault to the specific part at fault, rather than just noting the surface problem like the Snap off diagnostics tools.

Horizon81

Lum, it's a 1.0 VVTi engine, original sensors are made by Denso. If you think the first one is the one that is most likely to be at fault then maybe we'll change that one first. They certainly ain't cheap. The cat was £350, I don't think many places offer to weld up exhausts anymore do they.

Horizon81

TiTheRev wrote: »

Why not just take it to Toyota and get it diagnosed properly???

Most dealers do a fixed fee diagnosis, and if they can sort the problem within the alloted hour (for example) then you walk away with a cheap fix. If the diagnosis shows something else, like the cat or lambda, then you can thank them and take it to your fred in a shed to be fixed with cheap as chips parts more confident that the problem will be fixed. You never know, Toyota may be competitive

I really cannot understand the prejudice and stereotyping that goes on about dealers. Why are all 'independants' not branded cowboys like Watchdog et al might suggest?? There is good and bad in all trades, but at least if you get the diagnosis done at Toyota they will be able to trace the fault to the specific part at fault, rather than just noting the surface problem like the Snap off diagnostics tools.

I'm sorry but this is a load of BS. Personally I do take my car to a dealer but in my friends case its not worthwhile. I've actually spoken to Toyota at length for their advice, and basically all they's do is put it on the diagnostic reader and charge £50 to tell me the fault code I already know. They'd then suggest oxygen sensors, and failing that, a new cat. They certainly didn't say that their software is any more in depth than a standard OBDII reader. It's fault code P0420 and Toyota wouldn't be able to tell you any more than that.

Lum

Horizon81 wrote: »

Lum, it's a 1.0 VVTi engine, original sensors are made by Denso. If you think the first one is the one that is most likely to be at fault then maybe we'll change that one first. They certainly ain't cheap. The cat was £350, I don't think many places offer to weld up exhausts anymore do they.

The Denso ones are £48 each from the site I linked! I have no idea which of the two are faulty, it's a 50/50 chance, however a front one is going to actually cause damage so I'd probably start with that one.

As for welding up exhausts, I guess it depends where you live? Plenty of places here in the valleys will do it. I hope you at least insisted on them giving your old cat back, you'd get £40-£60 for it at the right recyclers.

AlexisV

Yes, but have you replaced the lambda sensors? They only last a few years and will need replacing at some point anyway if they've never been done.

colino

P0420 is a dripping roast for garages. Some code readers actually helpfully state, as well as the code, something like "catalytic convertor failure". Rubbish! You need the same technical expertise to diagnose faults as before, and I strongly suspect a huge number of healthy cats and O2 sensors are changed when the car really needed someone of experience to look at the car and find the exhaust leak that often throws up this code.

TiTheRev

Horizon81 wrote: »

I'm sorry but this is a load of BS. Personally I do take my car to a dealer but in my friends case its not worthwhile. I've actually spoken to Toyota at length for their advice, and basically all they's do is put it on the diagnostic reader and charge £50 to tell me the fault code I already know. They'd then suggest oxygen sensors, and failing that, a new cat. They certainly didn't say that their software is any more in depth than a standard OBDII reader. It's fault code P0420 and Toyota wouldn't be able to tell you any more than that.

This post shows a huge lack of understanding, and typical of the stereotyping that is banded around. A dealer diagnosis will not 'just tell you the faultcode you already know', but actually trace the fault and test the offending part, then if that is working to within manufacturers tollerances, will check the next part in the chain or a similar part that may create the fault. THAT is why a snap-off code reader is not as good a genuine, because it just reads the symptom not the underlying cause.

Horizon81

TiTheRev wrote: »

This post shows a huge lack of understanding, and typical of the stereotyping that is banded around. A dealer diagnosis will not 'just tell you the faultcode you already know', but actually trace the fault and test the offending part, then if that is working to within manufacturers tollerances, will check the next part in the chain or a similar part that may create the fault. THAT is why a snap-off code reader is not as good a genuine, because it just reads the symptom not the underlying cause.

All I can say is I've spoken to 2 Toyota dealers service managers, at length, and neither suggested anything different. Neither said that any of their software would be more helpful in detecting the fault. Both just mentioned oxy sensors and cat. Don't you think they'd have extolled the benefits of their software readers if they were somehow better in diagnosing the problem?

My local independent has inspected the full system for leaks (none found), cleaned the MAF sensor (worth a try for free!) so the next port of call is the sensors. They've recorded live data from the car running and the sensors are working but showing unexpected readings. So, it's either the cat has broken again, or the oxy sensors are at fault. Main dealers aren't miracle workers you know.