Hello - I'm new to Audi's and need some help. I recently bought a lovely 2010 Audi S3 Sportback. Gorgeous car. I've not long had it and the engine management light has come on; took it into my local garage and they said it's showing this error code - P0420 Code: Catalyst System Efficiency Below Threshold (Bank 1). [harsh to pay £60 just to get that info]

From what I can deduce; it's either an issue with the Cat or Sensors or both. Although first off; I will use a Cat Cleaner petrol treatment. 

So I have a few questions:

• Any tips on a good cat cleaner petrol additive to use in an Audi? Halfords sell Cataclean; ECP sell TopCat?
• Any other tips on resolving the issue without replacing either Cat or Sensors?
• If I do have to replace either of these; any idea on likely average cost?
• Any tips on a good value code reader to buy? (i won't be shelling out £60 the next time a light comes on)

Thanks in advance. I do very much appreciate any tips

 

Hi Graeme...welcome to the forum

Sorry for the late reply, only just read this post.

I would try a cleaner first, especially if the car is only smoked around town.

Firstly, I believe the fault is with a lazy sensor so a cleaner is a good place to start. I have previously used Halfords own cleaner as it looked the most aggressive with the most amount of Ethanol in it, along with an Italian Tune-up, worked a treat.

Let us know how you get on with it

Cheers  Trevor

Thanks for the response Trevor. I've bitten the bullet with my mechanic and am going to replace the o2 lamda sensors initially. He reckons it's more than likely issue with the converter; and that fuel treatment unlikely to solve the issue (although he would say that wouldn't he). But doing the sensors would be a must-do when doing the convertor anyway. My fuel consumption also seems higher than it should be for motorway driving, so that would probably point to at least a sensor issue. 

Got some longish journeys coming up - so just want a 'sorted' car. One of those things when you can't really look for when you buy a used car privately. 

Keep us updated on the progress and how it runs afterwards,  Cheers

So, here's a quick update. Welcome any one else's thoughts / experiences on this. 

- Didn't bother with the cleaner; reviews online were less than convincing. 

- I've since had both the sensors replaced. Expensive job at roughly £500 for the pair. 

- After 400 miles, the EML has come back on again - though this time i've now got my own code reader. 

- Just spoken to a mechanic; he's advised me that it's a dealer only part (the cat)

He also said a few other things, as follows:

- Do some research online; consider cutting out the cat altogether and having the ecu re-mapped

- Speak to a dealer; this may also be a software glitch (nice of him to tell me that after i've just paid for the sensors to be replaced)

- I'd also spoken to someone else who advised on alternative methods of sorting my CAT

So, to summarise. I'm no further forward; just £500 worse off :-( 

Any tips from anyone??

Should I now bite the bullet and take it into a main dealer?

Hello Graeme,

I'm sure there will be others more knowledgeable than me would be able to advise you, but I would ask what mileage this car has done, since my experience has led me to believe that original equipment catalytic converters are normally long lived components. I mention original equipment since I'm not sure whether you know the full history of this car or not. There has been a spate of cats. being stolen around these parts and I would just want to conform that this hasn't been fitted with an aftermarket replacement one, say due to this reason.

OK, you have been informed that the cats. are main dealer only, but have you actually checked the aftermarket market yourself - even continental aftermarkets? Fuel Parts were one UK supplier who do cats. and it may be worth contacting them for confirmation. Personally, I would be wanting some further confirmation that the cat. is at fault ( if genuine VAG) before throwing more good money at it. 

Back to the O2 sensors. Can we take it that these were genuine VAG replacements? I would hope so judging by the price! I think there might be generic replacements available for these and they can sometimes be of variable quality. 

Nothing concrete here I'm afraid Gaeme, but possibly a bit of background which might help. 

Kind regards,

Gareth.

For the sake of how much a bottle of CAT cleaner is going to cost I would be trying that now before parting with any more money. Get it in and floor it once it's up to temperature. If that doesn't sort it then at least any bigger spends will be more justified.

I am no expert on these sensors but I assume it's calculating the exhaust gases content before and after passing through the CAT matrix (just an educated guess), you have had the sensors changes so likelihood these are now at fault is very slim. So it makes sense that the Matrix needs a clean? Or a new one is needed. Magnets advice is good about trying other suppliers though, Audi will be very expensive.

So here's a quick update. No resolution yet, though too earlier to tell. 

- So, i bought a product called CatAClean. It's a petrol treatment. I'm now on the follow up tank of fuel. I do not however believe this will solve the issue. 

- I believe replacing my sensors was a waste of time and a 'con' by my local garage / mechanic

- Local mechanic now suggests taking car to an Audi dealer and getting a software update. He apparently spoke to a friend at an audi garage and they suggested that there are indeed software updates related to this fault code. 

- I've also just had the car serviced. Waiting to see if the light comes on again, before going to a dealer for a software update - but that is my next step. 

Note: for some folks, TerraClean may be an interesting option. 

Does anyone know anything about getting a software update applied to the car?