Confirming approach for P0420

[crazyone64]

Hi, this morning the check engine light came on for my 2003 mach1. 56000 miles.
P0420 - catalyst system efficiency below threshold bank 1

Many many years ago i installed 2 MIL eliminators which i believe is after the cats?
Bank 1 = passenger side on mustang

Could you please confirm that i can narrow it down to the passenger side, after the cat (which is closer direction to the tailpipe than the engine)

Possible culprits include:
1. Passenger Mil eliminator (after cat)
2. Passenger O2 sensor (after cat)
3. Passenger cat itself (after cat)

Any advice would be appreciated.

Thanks,

 

[89ripper]

What was your reason to install the mil eliminators? You are still running cats right?

 

[crazyone64]

What was your reason to install the mil eliminators? You are still running cats right?

Still running cats and i think the MIL eliminators were installed due to an error code. Can't recall the specifics 10-15 years ago

 

[89ripper]

Ok, im gonna post a couple links for you, some people say it could be cause from exhaust leaks so you might have to do a little digging

M

Thread 'Error codes (p0420) - possibilities?'

Nov 16, 2009

I have a 2006 Mustang GT and as of late it’s been throwing codes (P0420 and P0430 - catalyst efficiency below threshold both bank 1 and 2). I had it into the dealer (since it was initially hard to cold start and would produce smoke), the dealer said it was due to my AFE Stage 2 intake and oil filter which was over oiled and as such some of the oil had transferred onto the MAF sensor. They cleaned it and I had the same problem again, this time I purchased the AFE dry filter, sensor cleaner & throttle body cleaner and went to it on my own and cleaned everything out before reinstalling the...

• matty
• Replies: 3
• Forum: 2005 - 2009 Specific Tech

Thread 'P0420 code has me stumped'

Apr 25, 2012

I keep getting the P0420 code and each time I reset the ECU it comes back after 500 miles of driving. I realize the code is telling me the bank 1 catalyst is below efficiency, but I don't have cats and during my dyno tune my tuner shut off the rear O2 sensors.

What else could be causing this to happen? I recently replaced the IAC motor, I cleaned the MAF, I've checked for vacuum leaks and haven't found anything, there are no exhaust leaks, and the PCV valve was replaced last week (though not sure if it would have anything to do with this).

Now there is another issue here. My car won't...

• N8Dogg98
• Replies: 22
• Forum: SN95 4.6L Mustang Tech