MOT Failure
 

Hi guys just looking for some advice with regards my MOT failure. My car failed on exhaust lamba reading high and exhaust carbon monoxide content high after 2nd fast idle.
Does anyone know what I should be replacing to get these readings low enough to pass the MOT

Any help appreciated.

Need more information, oem cats, sports cat, no cat, mods, how far were the readings out etc

Sounds like sports cat, if is 100 cell like mine get it changed for 200 cell. Or try car cleaner.

Thanks for the help much appreciated. It’s got 2 cats on exhaust currently it has recently had a new back box put on with a bigger exit on.
But it passed last year with the same exhaust system with cats and smaller exit. so I’m guessing the cats are on there way out maybe. Would it need a another MAP due to bigger backbox on the car?.

If you have lambda values outside of the limits, it's probably nothing to do with cats etc. Even with a decat my lambda values were in the right range, but CO was way out.

If you have an OBD2 interface, you can read the lambda values as reported with e.g. Torques on a phone (assuming the obd2 interface has bluetooth). If the reported lambda readings are OK, but the MOT says no, then it's probably a lambda (oxygen) sensor issue.

If you can gain access to live data as suggested, check the lambda readings, with the engine off but ign on, they start to be above 1.0 when failing or heading higher,
Where a new sensor reads around the 0.80 mark,

100 cell is going to be a pain to get hot, as it flows so well, I struggle with a 200 cell, but a really good "Italian" tune up before sorts that.

Yeah, I would guess its a sensor issue rather than CAT failure if you still have both CATs in place. Replacing the back box doesn't mean you need a map either. It could be that you need some Cataclean through the system and give the car a good run keeping it in high revs to get the CATs smoking hot to burn off deposits. Either way, it is often the simple things that will make it fail emissions rather than the CAT itself.

I’m hoping it’s something simple lol it’s booked into Subaru but they can’t see me until next week . But in the mean time I can try the cata clean route to see if that helps with the readings
Are obd readers able to read things like that or are they just for lights on a dashboard? Thanks

Wouldn't be going to a main dealer you'll get shafted, find a reputable specialist in your area.

Obd and the likes of btssm can display all values from the ecu such as fkc and timing etc.. Really good actually

I find the main dealer depends on the mechanic working on the car, yes, they will fleece you sometimes, but the main dealer I have used has been really good. The MOT mechanic made a point of heating the car up for me so that it would pass emissions as I have a 200 cell sports CAT and it needs to be glowing hot to work well enough. As it also took so long to get it through, they fitted the 4 tyres I supplied without charge because I had to wait. Not many will go to any effort but I can't say all the deals are pants.

As said above though, the OBD readers are great and display real time info, very handy.

What I have found out after contacting many garages is that a lot of so called specialist garages want nothing to do with Subaru’s. I thought it would be a dream to be let loose on a car like a Scooby but perhaps I’m being biased lol

Then your contacting the wrong garages haha. Where are you? Sure someone can recommend a garage in your area or not far from

I’m based in Wiltshire the nearest specialist that I can see is Subaru’s 4u which is in Newbury but that’s to far for me to drop my car off for someone just to look at it especially now the MOT has run out, maybe there’s someone closer

A good Subaru specialist will save you no end of hassle in the long run, so it's worth driving a little further in my opinion. As long as you have an MOT booked and the car is safe I think it's legal.

http://tetburymotorcentre.co.uk/

They used to be a franchised Subaru dealer back in the day. Unassuming old-school garage. MoT all my cars there and give them my Impreza's when the job is too difficult or I can't be arsed :lol1:
If you book an MoT with them then no issue driving there on the day.