MOT emissions fail after secondary cat delete

[markjay]

.....but only if the vehicle does not comply with the emission standards it was designed to meet. This is defined by the MOT test....

This statement is incorrect.

The MOT test does not check your vehicle's emissions against the vehicle manufacturer's original emissions spec.

 

[ALFAitalia]

They do on a derv....the level it has to be under is stamped on a plate in the engine bay.....but not petrol's.

.....the 0.52 on the bottom right on this googled example. 0.5 on my car.

 

[DrNick]

You are not allowed to remove any factory fitted emissions equipment... illegal and an MOT fail with the same fines as above. But yes you are unlikely to be caught.

From the MOT testers manual.

a) Emission control equipment fitted by the manufacturer: missing, obviously modified or obviously defective. That's classed as a major defect and should be an automatic MOT failure.

...it matters not if it passes emissions or not.

Only if car first used after 2002. That’s my reading of the MOT page I posted earlier. As I said, I’m no expert and didn’t read the whole manual. Pre 2002 it needs to pass the emissions test that is appropriate. You can check my references as posted above and tell me where I’m wrong. I usually am but it’s not clear to me where, in this case!

 

[BTB 500]

You are not allowed to remove any factory fitted emissions equipment... illegal and an MOT fail with the same fines as above. But yes you are unlikely to be caught.

From the MOT testers manual.

a) Emission control equipment fitted by the manufacturer: missing, obviously modified or obviously defective. That's classed as a major defect and should be an automatic MOT failure.

...it matters not if it passes emissions or not.

That's not correct. Cars first used before 1 September 2002 can only be rejected for missing/modified/defective components where a full cat test applies:



A passenger car first used on or after 1 August 1992 but before 1 September 2002 gets a Basic Emissions Test (BET). If that's passed then no cat check is done:

MOT inspection manual: cars and passenger vehicles - 8. Nuisance - Guidance - GOV.UK

Noise, exhaust emissions, engine malfunction indicator lamp (MIL) (sometimes called an engine management light or 'EML'), and fluid leak rules and inspection for car and passenger vehicle MOT tests.

www.gov.uk

Since having sports cats fitted my 1997 R129 has passed the MOT for 10 years running. The first 8 of those were done by MB Guildford, the last 2 by a local garage here in Shropshire. No issues at either.

 

[DrNick]

This statement is incorrect.

The MOT test does not check your vehicle's emissions against the vehicle manufacturer's original emissions spec.

Maybe not literally, but effectively it does. It checks the legal limits that applied at the time of manufacture. You’d hope the manufacturer would design to a tighter spec than this to ensure compliance is met even as parts wear etc.

 

[markjay]

Maybe not literally, but effectively it does. It checks the legal limits that applied at the time of manufacture. You’d hope the manufacturer would design to a tighter spec than this to ensure compliance is met even as parts wear etc.

I wasn't referring specifically to the cat delete discussed in this thread - I just corrected your statement (and ALFAitalia pointed out that my correction only applies to petrol cars, not Diesel, which I did not know). Emissions (on petrol cars) are tested to a standard legal limit, and not against the vehicle-specific emissions data that the manufacturer provided when new.

Where does this leave owners who carry out cat delete, is not clear. In theory, if the car's emissions are now higher than the manufacturer's original specifications, then this would be an MOT fail (for post-2002 cars). But the reason that I say 'in theory' is that the MOT emissions test does not actually check the car's emissions against the manufacturer's data, so how can the MOT tester fail it?

With regard parts' wear, I don't think it comes into it, because from the legal perspective, I guess that you will simply be expected to replace any engine parts that have become worn to the extent that they increase emissions (even if it means replacing the entire engine...) - I.e. I don't think that legally there's any give for wear.

 

[Wolfie1]

On a diesel if the max emissions is .52 the limit for an mot is .57, .5 is always added into the permissible amount

 

[ALFAitalia]

That's not correct. Cars first used before 1 September 2002 can only be rejected for missing/modified/defective components where a full cat test applies:

View attachment 158175

A passenger car first used on or after 1 August 1992 but before 1 September 2002 gets a Basic Emissions Test (BET). If that's passed then no cat check is done:

View attachment 158176

MOT inspection manual: cars and passenger vehicles - 8. Nuisance - Guidance - GOV.UK

Noise, exhaust emissions, engine malfunction indicator lamp (MIL) (sometimes called an engine management light or 'EML'), and fluid leak rules and inspection for car and passenger vehicle MOT tests.

www.gov.uk

Since having sports cats fitted my 1997 R129 has passed the MOT for 10 years running. The first 8 of those were done by MB Guildford, the last 2 by a local garage here in Shropshire. No issues at either.

Agreed..I missed the age of the car and was referring to more recent ones.....but there are lots on this forum with DPF, secondary cat, EGR mapped out, Adblue mapped out. All of which is illegal, MOT failure and attracts a fine....and before anyone says, yes, you are unlikely to be caught....but the OP failed the test of course. For insurance reasons I would not remove/disable emission kit....just be my luck it gets spotted in an inspection after a prang....and I certainly would not admit I was driving an illegal and potentially uninsured car on an open form!!! Hopefully the Op got that insurance agreed in writing....as the people you talk to never seem to know much about cars and even people with newer cars seem to be able to insure illegal cars......until payout time comes of course!!

 

[DrNick]

So to be clear for those who drag this thread up after 10 years (like I did), despite the title of the thread, the discussion centres around secondary cat delete on the R129.

Currently (2024), R129s that were registered before 2002 (probably all of them but check your date) can have their secondary cats removed without falling foul of any emission related rules in the UK. Other countries may be different.

This does not mean that they will pass an MOT - the primary cat might have failed for example, but if everything else is ok they should pass emissions test.

There may be other rules that apply eg noise rules - those are not discussed here!

You should declare any such modifications to your insurer. In my case it was a box to tick labelled "Exhaust modification". No other details were asked for.

In my case it hasn't made a lot of difference to the sound. Possibly sounds a bit sportier under load, and obviously doesn't have the annoying broken cat rattle. I did it for convenience and cost reasons (and lack of availability of sensible other options like a new MB replacement).

 

[ALFAitalia]

To me...."exhaust modification" does not mean cat deletion......just a louder or different looking one. Hopefully you are covered in the event of the worst happening....but id want to be sure personally.

 

[BTB 500]

So to be clear for those who drag this thread up after 10 years (like I did), despite the title of the thread, the discussion centres around secondary cat delete on the R129.

Currently (2024), R129s that were registered before 2002 (probably all of them but check your date) can have their secondary cats removed without falling foul of any emission related rules in the UK. Other countries may be different.

This does not mean that they will pass an MOT - the primary cat might have failed for example, but if everything else is ok they should pass emissions test.

Worth mentioning again that some cars (e.g. my 1997 SL500) only had one pair of cats to start with - I believe the primary/secondary setup appeared in 1998 when the M113 engine replaced the M119 (Mercedes also dropped the centre muffler/resonator at that point).

There may be other rules that apply eg noise rules - those are not discussed here!

In my case it hasn't made a lot of difference to the sound. Possibly sounds a bit sportier under load, and obviously doesn't have the annoying broken cat rattle. I did it for convenience and cost reasons (and lack of availability of sensible other options like a new MB replacement).

Noise level is just a subjective assessment at the MOT:



As I understand it a car has to be pretty obnoxious to risk a fail here - mine still sounds mild compared to many other cars in stock configuration. As mentioned it was MOT'd by a main dealer for 8 years after being modified and the only comment I ever got was an unofficial one about how nice it sounded!

You should declare any such modifications to your insurer. In my case it was a box to tick labelled "Exhaust modification". No other details were asked for..

100% and I can confirm that no insurer has ever wanted to know what changes have been made to mine - the question is simply "has the exhaust system been modified, yes or no?". They're not interested in any details. Same with wheels - they're either factory standard ones or not ... that's all they care about.

 

[neilrr]

Had the two rear cats deleted on my 500 last week...

Why?

 

[DrNick]

Why?

Started to rattle. Choice was replace whole front section (2 cats a side) with after market pattern parts from BM. Given that the ones on there were already these and the secondary cats had only lasted 3 years, I didn't see this as a long term solution. Also fitters are not that interested in fitting them so I would have to do it myself or some other arrangement. Also as one side had gone, there was no guarantee that the other side would be ok for much longer, meaning I'd probably end up replacing the other side as well soon (added cost and pfaff).
Or I could have aftermarkets cats welded in. Again I'd need both sides to keep balance. Would work but was pricey and then if the BM front cats went later, I'd have these new cats tied up in the old pipe.
Some research showed that it was an option to remove the secondary cats (or gut them, which feels obviously deceitful to me) and I decided removal was the least painful and most convenient solution at the moment, given it was not long to the MOT.

Down the line, and depending on how long I want to keep the car, getting new primaries welded in (when necessary), or even getting a SS exhaust done may end up being my options.

As it stands though, I hope it should be good for about 20k miles before I would normally expect any other issues, and that is years away!

 

[pcthrillrider2]

Just had my R129 fail the MOT on emissions after the secondary cat delete I had done in April. Car has done under 700 miles since the previous MOT, which was fine.

Luckily I'd put it in early just in case - I've got till the end of the month to get it sorted.

I've not heard of anyone else having this problem?

Just to be clear, it failed solely on the emission readings. Not the fact that it only had 2 cats now rather than 4.

By the way if your car fails the mot your mot is invalid!

 

[markjay]

By the way if your car fails the mot your mot is invalid!

This has been debated here many times, and it seems that the the DVSA are vague on this. The wording is that if the car failed the MOT then "you can take it away". Most people understand this to say that you can drive it away, but equally you could argue that the car should be taken away without actually driving it (e.g. towed away). To my knowledge, the DVSA have never provided any clarification. The situation de facto is that most people believe that if the fault wasn't clarified by the MOT tester as dangerous, then they can keep driving the car (as long as the original MOT has not expired yet). Of course, this can potentially affect the insurance, if the insurer deems a car with failed MOT as unroadworthy.......

 

[ALFAitalia]

By the way if your car fails the mot your mot is invalid!

Not true and never has been. It does NOT invalidate your current MOT either.....if its just a fail. However your car does have to be road worthy so if it's failed on your tyres being down to the wires it clearly can't legally be driven.
If you go to the mot gov website after a fail it shows the fail.... but still shows your old mot as valid until its expiry date.

 

[Wolfie1]

If your car gets a “dangerous fail” it is no longer legal to drive on a uk road even of you still have time left on your current mot, if you are stopped by the police you will be charged, if you get a major fail thats where it gets hazy about driving it

 

[ALFAitalia]

Agreed... in the same way you are not allowed to drive any car on the road that is in a "dangerous condition" MOT or not.....but the old MOT is still valid until its expiry date.

 

[Aristo]

You don't seem to see MOT stations doing 'pre-MOT' inspections any more, which always makes the annual event a bit more anticipatory than I'd like - I'd like to know what they think is wrong before the official recording, but haven't seen this in years now. Maybe it's not allowed any longer

 

[ALFAitalia]

That's why lots of people link the service to the MOT date.....so all the MOT items are fixed before the test.......its how you get rubbish cars with spotless MOT histories!!! Pre mot checks are allowed.....but lots wont do it as at over £54 for the test alone, for many that's expensive enough without adding extra labour costs of the pre check to a car that might pass anyway......its not like it costs anymore to fix it after the test.
Its not that difficult to check most of it yourself, just download a list from the net and check it through......you would be amazed how many tests fail on really silly stuff that people should be noticing in their day to day use of the cars.......bulbs out, bald tyres, seats belts not rewinding, obscured view of the road etc.....no excuse for failing on that stuff really. Sure you might not be physically be able to lift the car and check for suspension play etc....but as least you know it wont fail on anything silly with a quick check over.

The most common MOT fails and how to avoid them | RAC Drive

To help you pass your MOT, we have taken data from the DVSA, to reveal what the most common MOT failures are - and how you can potentially avoid them.

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