Failed MOT :(

Hi Everyone
I have had my little 1999 Jimny for 10 years. It's always struggled with rust as they all seem to do. I have a bit of welding to do this year, that's no problem as I have all the kit to do it.
Emissions are my problem..
I replaced the front cat about three years ago, some 10k miles it only has one on my car in the front section of the exhaust pipe. But Its failed again on high emissions. is this likely to be the cat again or could it be some sort of sensor, I am not educated in all this fuel system magic. I can weld it and mechanic it but the emissions are an enigma to me.
What should I be looking at.. sensors or just a new cat?

all help appreciated.

thanks

Did you see the fail report?
Assume your CO was high, but how was the HC and Lambda?
Could be the lambda sensor, could be the CAT, may be able to guide better with the report.
Mike

Mike
I will check in the car to see if they left it in there. thanks for the advice so far.

Mike.
Looked at the report and it’s saying carbon monoxide 2nd fast idle exceeds default limits.
That’s all it says on the major defects..

Ok I was hoping they had left the emissions tester print out (looks like a till receipt) attached to the MOT report. It tells you everything that was going on, it's an interesting read.
Without this it's difficult to know what the actual CO was (at fail) and what the HC (the CAT to some extent) was doing at the time.
It's possible it's a slow Lambda sensor, but a totally failed Lambda would also give idle CO limit fail which you don't have.
Sorry but I am not sure.
Possible Lambda fault, could be CAT. How old is the Lambda? They don't last forever.
Mike

Hi.
I think that the Lambda sensor is original to the car. So it could be that or the cat.
The engine warning light, lights up on start up but goes straight out. what does the eml monitor on the car? so is it possible that no fault codes are being generated..
I will order a new sensor.. what other sensors if any should I look at on the car.
General performance is okay, runs well, puff of smoke on start up.. she only does short journeys these days so it could be that as well.
I may as well get.

thanks