MOT Failed - LAMBDA sensor and Catalyst?

[buckaroo]

My VW Golf, has just failed its MOT on the LAMBDA Sensor and catalyst, which I need to replace.

Are these really expensive??

I also need to re-MOT test and service, and just wondered if anyone here would recommend a good garage to do all 3?

 

[Burnerman]

These parts can be cripplingly expensive from a main dealer, but they are available from a motor factors for a much more sensible price. Try the Eurocarparts website, and tap in your registration number.
Use a genuine lambda sensor though (against a universal one) and any independant garage will be able to fit both for you.
John

 

[gblades]

Burnerman, what would be your thoughts on getting the lambda sensor replaced first and then taking the car for a long blast along the motorway?

Could the cat be sooted up do you think?
I know if the mixture is too rich you get unburnt fuel in the cat which does kill them.

The cat is by far the more expensive component so just wondering if that would be worth a try.

 

[Belle427]

post the readings that it failed on and we can give better advice

 

[buckaroo]

On the emissions sheet (and I was told it was the Lambda)

So on the 1st fast idle test and 2nd idle test the CO% and HC ppm say "passed" on both.

In both tests on the Lambda :

1st fast idle test :

Lambda limits : 0.97 / 1.03 Actual : 1.64

2nd fast idle test :

Lambda limits : 0.97 / 1.03 Actual : 1.60

Although the garage said I need both (they would!) but did say I might get away without one?

But here's the Failure Items as listed that i'm to replace to get a good chance of passing the MOT:

1. Exhaust emissions LAMBDA to high Catalyst £325

1. Replacement Catalyst Convertor LAMBDA sensor. £90

Seems a bit steep...

 

[Belle427]

what year is the car? If the engine is in a good state of repair and well serviced, and the exhaust system is leak free i would be inclined to stick a tank of super unleaded in it and take it for an italian tune up
this usually cures a lot of emission related failures

 

[buckaroo]

Hi, the car is year 2000 and has around 90k on the clock, as its not used much probably under 10,000 a year if that (I use wife's company car)

Do these Lambda figures make sense?

So a full tank of Super Unleaded, and an italian tune up means revving it and speeding up the motorway and back?

(have i got that right?)

 

[Belle427]

if your sure there are no exhaust leaks (Particularly around the cat area) then yes a good blast will help. An engine service should help too, always try to make sure the car has been for a decent run before the mot so the cat is red hot

 

[buckaroo]

if your sure there are no exhaust leaks (Particularly around the cat area) then yes a good blast will help. An engine service should help too, always try to make sure the car has been for a decent run before the mot so the cat is red hot

Not exactly sure where the CAT area is? but all i know is that there are no leaks on the drive? (but i suppose this would only occur when its running and pumping out exhaust fumes?)

I could leave running on the drive for a while?

I am due a service in the next month or so as its due in about next 1000 miles according to the onboard computer - but would it be advisable to get this done first? then put in for MOT say the next day but then go for a long run in it?

 

[gblades]

If the CO and HC both pass then I can't see there being an issue with the cat.
The lambda measures the oxygen so is a guide on how efficiently the engine is running. I am not sure which way the scale runs. I would say either your sensor is misreading causing the engine to mistune itself or you have something else wrong with the combustion process. Most likely it is the sensor and once fixed you should notice an improvement in performance and fuel efficiency.

 

[gblades]

If it's not the sensor at fault then maybe a leak in the exhaust manifold (the lambda sensor is normally connected about where the manifold connects to the main exhaust) or a faulty or dirty spark plug causing unburnt fuel and air to enter the exhaust.
There are lots of guides on testing the lambda sensor if you can get to the contacts easily.

So my advise would be to get it serviced first especially if new spark plugs are due and then get the emissions checked and if still out then the lambda tested or just replaced. Normal lifetime for a lambda is apparently about 100k miles but my old BMW did 195k without needing one and a friend changed one on his car which failed at 200k.

 

[jezsherwood]

I would go for Mass Airflow Sensor failing. Oh and new air filter if you haven't already.

Common as poo on VW Audi group. Any decent garage would check it and would be done by driving car and logging g/s reading through obd port.

Lamda's show up faults in the system and when they fail they normally go completely.

As said earlier, cat seems fine, Lamda can be checked with a meter.

 

[Avocet]

The lambda readings suggest that the engine is running weaker than it should. It's hard to tell if te cat is poorly, just from that. The lambda side of things (as has been said) is completely independent of the cat. If CO and HC readings are within limits, it suggests your cat is probably OK.

You need to find out why it's running weak (or why the gas analyser THINKS it's running weak)! I say that because the MOT gas analyser probe goes into the tailpipe - a long way "downstream of the cat". If there is an air leak anywhere in the exhaust, between the lambda sensor and the back of the exhaust tailpipe (which the garage should have spotted), it will fool the gas analyser into thinking that Lambda is wrong. That's the first, and least expensive thing to check.

Assuming it is gas-tight, it could be the lambda sensor itself, or, as has been suggested, the airflow meter. There could be a variety of other reasons too, I'm afraid. Sometimes, it's cheaper (in the long run) to bite the bullet and go to the "main stealer" with proper diagnostic equipment.

 

[jezsherwood]

Nooooo! Don't go to the stealer, they will more than likely charge you a diagnostic fee and want to change the lamda just because the computer says so without bothering to find out why it's readings are out, it's good for a quick buck.

Go to a VW independant who will know what they are doing and are generally cheaper and more sympathetic. I realise there are some very good dealers out there so I apologise to anyone here i might have offended.

I would register with a couple of VW Audi group forums and get recommendations of decent garages.
You can PM me for a couple if you want.

I do appreciate you only have limited time to sort it before you will need a full re test.

 

[buckaroo]

Thanks for all your tips, yes your right time is running out for my re-test!

I have heard of this sort of thing before and think that it sits on the drive whether it was just cold and not used as much?

Also hear of someone (and many others) failing MOT with £800+ of repairs needed.. Then when they took it for a re-test, it passed?!

Maybe I should book my MOT further away and brun off the ommisions just before its re-tested, that way it 'may' pass!

Anyway i'll PM you now..

Thanks you!