P0420 Catalyst System Efficiency Below Threshold Bank 1

[mickgall]

Hi all

I've got an 02 freestyle and the EMU light has come on and won't go off. Had the Rac look at it and a p0420 catalyst system efficiency below threshold bank 1 fault was diagnosed.

The car runs fine and there are no noises or judders. The RAC think it could be an O2 sensor. I've done some searches and most posts seem to agree with this. How hard is it to replace? It looks fairly simple, like removing a spark plug but with a lamada socket and unplugging/ plugging in the connector. Is it as easy as it looks?

have attached a pic of the sensor

Any help greatly appreciated

Mick

[wase16ll]

think that is suggesting the after cat sensor

code is referring to catalytic efficiency, which is monitered by the after cat sensor

[Mr Singh]

how many miles has it done and what kind of driving are you doing?

if your doing short journeys then it could want a good italian tuning (a good thrashing), my grandads seat leon had had the same code come up twice before and the car is stood more than its driven and when it is driven its less than 5 miles.

[mickgall]

thanks for the replies guys, the light came on as I was driving along the motorway. The car is used most days on my work commute (40 mile round trip).

mick

[Mr Singh]

id then recommend the cheapest option, replace the O2 sensor

[mickgall]

yep thats what I thought, try the cheapest thing first

[wase16ll]

just to be clear

that code is suggesting a problem with the post cat sensor, the picture you posted is the pre cat sensor

[mickgall]

where abouts is the post cat sensor?

[mick85]

Bank 2 after the cat

[wase16ll]

think from memory its on the downpipe after the cat, but either way, looks exactly the same as in the pic so will be easy to spot.

although they look the same, they are actually different so need to confirm which sensor is producing the code...but the code states cat efficiency below threshold,,,

this implies either the cat is failing or there is a problem with the after cat sensor/wiring....the pre cat sensor cannot monitor the cat efficiency

mick, as its only one bank...will actually be bank 1 sensor 2

[mick85]

Ha my mistake I always had In my head bank 1 before was just my way remember which was right sensor ha bank 2 only on v6 or v8 correct me if I wrong

[wase16ll]

thats correct :)

[mickgall]

ok peeps

a quick update, following wase16's advice (whats the point of asking for advice if you don't follow it) I changed the post cat sensor - which is the one under/bottom of the engine and the fault is gone. So hopefully it's cured.

Mick

[Capri280i]

Hello. Just in case it helps. I had this problem a while ago and ended up replacing the cat, the 2 sensors, and even the sensor in the head. None of these cured the problem. At the MOT we could not get the emissions passed.  My friendly local mechanic noticed a grey line inside one of the rubber plug caps. It turned out that the spark was tracking outside the plug. Although the engine seemed to run ok. I replaced the plug with new, and since then and many, many miles later no more problems. It may be the fuel was not burning cleanly throwing the readings out. A set off plugs in the beginning would have saved a lot of money. But you live and learn.