MOT Fail...emissions! Advice Needed

[Chefoo]

Hi All

My LCR failed its MOT yesterday...

The tester said that they found a small crack in the exhaust and this would most probably be why it failed.
However ever since i bought the car a year ago it always had the fault code
P0420 Catalyst System, Bank 1 Efficiency Below Threshold

Now i always thought that this was because the exhaust wasn't standard and this was causing the Lambda sensor to act up and throw the EML, as i haven't put a spacer on the sensor. Its got a cat i should add.

After searching the forum im now even more confused than before, so i was just wondering what people thought, is the fault code the lambda sensor needing replacing or will welding/ fixing the cracked exhaust fix the high emissions.?

Many thanks in advance....

 

[swedey21]

Front lambada sensor?
Usually they throw that code IF you aint got a cat I THINK!...but if you have a cat..

How many miles?
Ive read that past 100k its advisable to replace.



EDIT:If the mainifold is cracked..i would get it welded..is it not blowing?
If it was blowing then i would have thought that it will confuse the ECU/emissions
EDIT...i see your local,ive got a spare sensor if you want to try..PM me.

 

[Chefoo]

It's just touched 50k, I'm I right in thinking a knackered lambda sensor would mess with the air/fuel mixture causing excessive emissions.
Many thanks for the offer of testing on your spare sensor... If it fails after the retest I'll send you a PM, is it easy to change? Just plug and play so to speak?

 

[swedey21]

Yeh dead easy..
Just behind the charge pipe in a LCR.
23mm spanner.

Yes the sensors in charge of the mixture,and can cause it to run weak/lean.

 

[James D1]

how far over the emissions were you? if its only miniscual a good run / fuel cleaner can sort you out.

new to these cars but id imagine a lamba is simple as with most others

 

[Dan1720v]

22mm is a lambda sensor.

The first low speed idle test showing high co says lambda sensor. the second fast idle test, where lambda is out says the exhaust leak.