Exhaust emissions, cat replacement ??

[UK Damo]

Ive owned my VW Golf GTi 2.0 (2000) 68K a couple of months, last month i posted on here regarding the exhaust emissions light lit up.

After running VAG COM it came up with the following fault

16806 - Main Catalyst : bank 1 : Efficiency Below Threshold
P0422 - 35-00 - -

After a bit of research i decided to change the front lamba sensor, I did cleared the fault and it didnt return imediatley,

I generally drive my car to and from work every day and a round trip is about 10 miles. The other week I took my car on a longer trip than normal approx 30 mins each way and the emissions light lit up on the way home. anyways didnt think much of it so I cleared the fault.

today took my car on another long run and yet again the light lit up,(Im guessing when the cat gets to a certain temp that it doesnt normaly get to on a daily basis it brings up the fault) I scanned the car again today and it came up with the same previous code and another one to do with engine miss-fire. if im honest the car does smell rather 'fumey'. If it helps the car was MOT'ed in may and passed no probs.

Im no car expert but is the miss-fire likey to be cause by a broken CAT ? any help would be greatly appreciated.

[Devondan]

Hi, not sure about the Golf, but my Punto had that prob abd it turned out to be a leaky exhaust joint, a cheap easy fix! Worth a check esp if you can smell fumes.

dan

[UK Damo]

Ok Cheers, i'l check it all over a bit lata. But I have a feelling its going to be alot more to it than that.

[orienteer]

get a VAG-COM cable and software and check your post cat is working correctly.

If it is it looks like it is indicating a worn out catalytic convertor.

Regards, Ian

[Crasher]

VAG cats rarely fail, if it is below efficiency you need to ask why. If you fit a new (presumably cheap aftermarket) cat and you don’t rectify the cause of the failure, the new cat will fail quickly and will not be covered by the warranty.

[UK Damo]

Im not saying im going to change the cat, it was just an option. After changing the front lamba which i thought would be the most likely fault where do I go from here ?

As Ive said in a previous post im no expert. The car is smelling rather 'fumey' though and whilst im driving im sure I can hear a slight vibration/rattle coming from the exhaust area.

When I scan the car with Vag Com and theres no emission light on I get no faults, when the light is on the only fault I get is 'Bank' 1 below threshold. Also I got a enigine miss-fire fault the last time I scanned when emissions light was on.

The light only ever comes on when the cat gets to a hot enough temp im assuming as I drive it round town and to and from work and no light, take it on a motorway at a consistant speed and 20 mins lata the light appears.

[Crasher]

What is the cars engine code? That fault code you have is detected by the after cat lambda sensor.

[UK Damo]

Aqy

[keithwigley]

Dodgy petrol? If you only buy from one source, especially supermarkets, the quality is minimal for performance engines.

[UK Damo]

Its possible, but id be very suprised. I use many different fuel stations. the fumes the car is producing at the minuate are very strong and are even worse when the car gets warm on longer runs and possibly causing the engine to miss-fire.

[UK Damo]

Has anyone got anymore thoughts ? Any help is greatly appreciated

[Crasher]

I would be inclined to change the after cat sensor to see if it is simply that, we have done a few.

[UK Damo]

Cheers for the speedy reply, I was under the impression the post cat sensor is just a data sensor which would trigger the warnging lamp. If this is the case this wouldnt cause the very fumey smells im getting would it ?

Also i need to change the cam/timing belt as my car has 68K on it and as far as im aware it has never been changed. Ive read on hear some wear that you might aswell change the water pump at the same time, is this true ?

Mines a 2000 X, Golf GTi 2.0 115 bhp AQY engine

[AwesomeSarah]

There can be a few reasons why the cat symbol comes on
It could also be MAF related
If the MAF thinks that there is a certain amount of air going through , then the lamda will adjust the fuelling to suit it
But then.....if the MAF is reading wrong , then it could be over fuelling
So with the coolant temp sensor too (but there is usually a code come up if that is faulty)
But the MAF does not always show a fault
So the fault will then lie with the lambda
I would say get more checks done , and check the MAF while it is running
Sarah

[UK Damo]

Ok cheers, you will have to excuse my ignorance here. But how do you check the MAF whilst running, do you mean VAG COM whilst running or physicaly check ?

[Crasher]

The post cat lambda allows the ECU to monitor the cats performance and apply corrections to make it run cleaner.

[UK Damo]

Ok that could relate to the iffy fumey smell im getting. Im getting the car put on a two pole ramp this week, So hopefully I might beable to pinpoint the problem.

Cheers for all your help

[Crasher]

Yes it could.

[con1981]

did you get the problem sorted my g friends 1.616v is having the same problem and garage is suggesting replacing the cat as well

cheers

[Crasher]

Cats don’t just fail, something makes them fail. Replace a genuine VW cat with a cheap aftermarket unit without finding why the original failed and the new cat will fail very quickly and will not be covered under the cat manufactures warranty.

[kan4u2]

MK4 Gti simular problem emission lamp came but car runs okay no miss firing just worried about warning light how would VW charge for putting on computer ? Steve :confused:

[Crasher]

Could be any one of a dozen common issues, a fault code read at VW will cost about £80, about £30 at a specialists.