check emissions error code P0420

[Lovell]

hello,

driving home the other day down the motorway and suddenly the engine management light and check emissions came on the dash. i've had it plugged in and its given the code p0420. the car has a sports cat fitted but thats been on over 6 months without issue. I'm hoping changing a lambda will sort the issue but unsure which one to change pre or post cat any ideas? thanks

 

[Siliconsteve]

Could be either. Or the cat. You need to see live data from the sensors

 

[Micah]

There's a link on here somewhere with all the fault codes. Think it's under Technical.

 

[turkie172]

P0420 Catalytic converter operating fault most likely if the car is running OK the second lambda is faulty and checks how the CAT is performing I had a problem in a 172 that the heating element in the second lambda was not working and getting unbalanced readings and activating limp mode and light if driven smooth at low revs and on wet days with standing water about. The Renault clip right way said the second lambda heater was not working I also had around the same time a faulty injector which I found by checking the resistance across the pins of each injector and found one that was different they were £32 each so I changed them all at the same time.

 

[Foxspeed]

clear the code then unplug the second sensor and see what it throws up