Has anyone experienced this error code P420, "catalyst efficiency below threshold bank one"? Does this mean my cat is bad? It comes and goes...usually after a restart while the motor is still warm. The strange thing is that I could start driving with a cold motor and go all day without tripping this code.

 

I have posted in the 'nitrous users' thread as well, but the basic gist is that, yes, your cat is on the brink of failing. I personally know of 2 people who have had the same problem as you and had to end up getting new headers. The code is intermittent at the moment, but needless to say, it will most likely become more insistent with time .

Henry

 

but could also be the 02 sensor. I'm sure it's the more expensive one thoght!

Matt

 

The more expensive one

 

Here's what I've found on the net:

• Leaded fuel was used where unleaded was called for
• An oxygen sensor is not reading (functioning) properly
• The engine coolant temperature sensor is not working properly
• Damaged exhaust manifold / catalytic converter / exhaust pipe
• Retarded spark timing

-Leaded fuel?...never got near leaded fuel
-O2 sensor? Maybe...
-coolant temp? I have thrown codes relating to temp below threshold that might be related to my M7 180 degree thermostat
-damaged cat?...crap!
-retarded timing?...this whole thing is retarded

 

I had the same thing with my Miltek and they recognized the problem and sent me a new one...I had to pay the labor....3-4K ago and so far so good

 

 

unfortunately this is a known problem with the CATs that Milltek use and there is no cure. Typically they last 10-30K before burning out, which is pretty rubbish really, especially if you are footing the bill . My advice would be to get a header with removeable CAT (like me ), that way, the financial impact isn't so bad when the CAT finally does give up the ghost.

Cheers,

Henry

 

I don't know if you are indeed using the Miltek header but if so, I have also heard that the performance goes downhill after around 10,000 km of use. This is a quote from an email I got from Volker at MTH.

".....The 200 cell cat is not really durable and melts
after +/- 10.000 km thus decreasing power again. Also the inlet ports
do not fit 100% with the outlet ports of the cylinder head. That was
at least the case with all Milteks we saw so far. I know it sounds like
cheap sales man talk, but if you want power and torque and durability,
we can only recommend our own MTH manifold because it is designed and
built to work best with the tuner file. Using a special 400 cell cat
it also means that it will last. ........."

Obviously they are plugging their own product but good info, nonetheless.
keep us posted on what you find out.

 

Where can I find out more about your product? Not that I can afford another header


SpiderX...How long did you have yours before failure and did they give you a new one on the house?

 

Sid, Its not my product, (nor do I have one installed) but you can email Volker @ vk@mth-powerchip.de

he can tell you everything you need to know.

 

Do they have a site?

Thanks:smile:

 

Yes Sid...they gave me a new one at NC. I guess I had mine on about 10-12K....this is supposedly a better unit that the original but who knows

 

And it's got capacity up to 390 cu in!

Matt

 

Who did you talk to Bob? I need to make a call:smile:

 

What is the name of the distributor.....Stratmoshpere?

Hell Sid just call me 404 277 7636

 

I'll call you after work:smile:

 

Hello all, I have been following this code 0420 posts for a bit. I have an Alta header that has been on for quite a while, about 4 years. However I only have 39,000 miles on my car. Anyway I have been getting the code at random intervals recently. I had a custom tune done as well. I was told by the shop that did my tune that maybe the cat is failing on my header. They suggested that they could weld in a racing cat for around 300.00 including labor. I called alta about the code and they recommended a bung whole spacer for my 02 sensor. To me that doesnt sound like a reliable fix, but I really do not know what is going on. I think I am going to have a new cat welded in at the end of the year, to see if that fixes the problem. I was writing this post to see if anyone else has done this fix, and to make an alternate suggestion to others who have had the code as well. Like I said I am not an expert but I just dont feel a 12.00 bung whole spacer will fix the problem indefinatley. Any feedback would be appreciated.

 

I know this is an old post but by chance, did you find a solution? Or did the CAT become the solution ? Thanks

 

Cel popped up on my drive home from work and got this code. My car is completely stock . Any data points pointing to a bad o2 sensor or is this definitly my cat going bad ?

If it's the 02 sensor anyway to know which one ? If not, what am I looking at if I need to replace the cat??

 

How many miles? R50 or R53? Been burning any oil?

 

You have emission testing/visual inspections?

 

Almost 103k miles . R52S. Changed oil about 1k miles ago and checked it last week. Doesn't seem to be burning any oil

 

Yes but it's once every 2 years and I just passed about 6 months ago

 

That code can be caused by upwards of eight different sensor errors including coolant temperature and MAF. IMO you need to get the voltage readings off the downstream O2 sensor to determine if that is the cause before throwing money at it. Two NAM Vendors also have full service shops so perhaps either Detroit Tuned or Way Motors will chime in with their experience as they have probably both have forgotten more about MINIs than most of us will ever know.