Engine Light PO420
 

2002 X5 3.0l has engine light on, had dealer check for code and they said it was PO420 "Catalyst System Efficiency below threshold"
They said that the vehicle appears to have aftermarket Cats on it and the O2 sensors do not like what's coming at them. They wanted $1500.00 per side to replace them. I brought it home and checked myself as I just got the EV 327 OBDll scanner, it verified the code!
I noticed the readings on one bank were as follows Long term fuel trim bank 1, -2.3%, all others were 0%. Is it the aftermarket Cats causing the problem or O2 sensor? Some Cats are constructed with better metal than others!

Just joined the site & love it!

Cheers
Don:dunno:

What brand are the cats? Myself and many others have been using Magnaflow cats on our 540/740's for years w/o issue. Is this car new to you or has it just started happening?

The mounting location is critical, meaning that the stock cats are much longer than the Magnaflows. In my situation, the shorter cats had to have about 2" extensions put onto the inlet/outlet in order to keep the cats center between the 02's, just as the stock ones we're. If not, the flow differences will cause a CEL to come on.

On a side note, unless your car has over 100k or more, the cats shouldn't really be giving you issues in the first place unless you've got a lack of maintenance and/or software issue causing the cats to get clogged due to the engine running too rich. If the aftermarket cats are failing as well, you may have other issues going on. The 3 series uses the same engine, so you may want to spend some time over on www.bimmerforums.com in the 3 series forums and see what experiences they've had.

I'll check the brand of Cat and add extensions if need be!
Vehicle has just over 200,000 Km's on it & is new to me!

Thanks,
Don

Have u tried rolling it up and smoking it? :p

Huh!

He was referencing smoking weed since your code is 420. He drives a Prius, so he's all about being green. Moving on...