Hi all , Im looking to put a downpipe/decat and a cat back system on tomorrow . Someone has told me I will need to get the ECU mapped to comadate the decat for the sensors as the wont be picking up anything . Is this true ?

Yes, without a remap your check engine light will come on after just a few miles. The ECU will not detect any difference between the lamda probes and throw a fault light.

The car will drive fine, however it will fail a MOT test with the light on even if it could pass an emissions test (which it won't without a cat). Having the fault light on all the time will also mask any other faults, possibly major ones should they occur.

A far better solution is a sports cat as this will keep the fault light off and will also pass an MOT (Just).

Any car that should have a CAT fitted and hasn't is also a failure wether the emissions pass the test or not. So if you can afford it get a sports cat as it will save hassle in the long run.

This will also save you on any VOSA road side spot checks.

I see , The car is re-mapped already , will i have to go for another re-map to stop the light coming on ?

you might find thelight stays off as some decat pipes ( ebay ones) seem to have spaced the rear sensor back slightly so it stays off

a few peeps i know have not had lights but then alot do

to get the most from a decat the map would need tweeking

hth

This is a ebay decat so maybe lucky and it wont come on , fingers crossed

buy a spacer off ebay to space the probe out abit,

I used to have a decat on my volvo and it would put light on ever fre thousand miles but i just used to knock it off as i had access to diagnostic stuff

Will ive had it fitted and no light yet but ive only done 3 miles ! Very happy with it and the noise isnt to bad .