Author Topic: P0420 Code Surviver!!!  (Read 10157 times)

Offline FantaSTIc_04

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  • 2004 Blue WRX Sti
P0420 Code Surviver!!!
« on: November 15, 2012, 07:37:51 PM »
If you click on this, you came to the RIGHT place! **How to Diagnosis and Fix P0420 Code!!!**

-Have you ever had that problem where you just drive normally or just cruising on the highway, and all of a sudden your (CEL) Check Engine Light starts blinking as well with your Cruise Control.. Feels like your car is jerking, hesitating, running lean, minimum throttle response, or worst losing power? 

1. o2 sensors are bad
2. Catalytic Converters are clogged or internals are deteriorated over years
3. Exhaust leaks
4. Coolant is low or not well balanced
5. Fuel cap isn't well tighten
**These are the most cheap, easiest and efficient steps to Diagnosis the infamous P0420 Faulty Code.**
=         =          =         =         =         =         =         =         =         =       =        =         =       =        =          =         =           =
1. Checked all of the symptoms listed above, but still have the same Faulty P0420 Code. (CEL)
2. Go to your local Auto Parts store and BUY a SPARK PLUG NON-FOULER. **I recommend getting the part #42009 with the 2 washers**
3. Drill 1 of the SPARK PLUG NON-FOULER with a 1/2 inch drill bit on the very tip. You're just basically open up the Spark Plug Non-Fouler for more flow and also for your o2 sensor can fit inside.
4. Reset your ECU by disconnecting the battery cables, remove the Downstream o2 sensor.
4. Assemble the 2 Spark Plug Non-Fouler together; the one you just drilled and the one you haven't. Including the 2 washers!
5. Install the final product to your exhaust system, reconnect everything. Your problem will go away after the 2nd or 3rd drive!
**It should look like this after you're finished** See pictures below!!!

More educational reading, MODS:
Do You Have a Cold Air Intake, Test Pipe, Headers, High Flow Cat, Downpipe, Catless or High Performance Exhaust Installed??

-99.9% of the time P0420 and P0430 CEL Error Codes Are Associated Only With The Post  (rear) O2 Sensor in modified exhaust systems (in or after the cat).
This sensor is also known as the 'Heated Sensor Circuit' or 'Bank 1 sensor 2'.

-With a Modified Exhaust System, the Post Cat Sensor receives A Higher Exhaust Temperature and A Higher Exhaust Flow Unburn Rate than Stock Exhaust Systems. This causes the ECU to read that the exhaust system is out of balance. When the ECU sees that the system is out of balance it throw's a code and drops into 'limp mode' (safe mode). When you add this Mini Cat O2 CEL FIX onto the Post Cat O2 Sensor, it will Convert Noxious Exhaust Gases and send the ECU the expected exhaust reading, Just As It Expects.. Thus allowing your ECU to run Your Engine Optimally to Produce the Added Horsepower. This causes the (CEL) Engine Light to appear!

If this helps you please feel free  to stop by and say Hi or Thanks! Much appreciated, I love to help others whenever I can. I also have the same problem as this, and now its all fixed and runs like a beast! :D  :subaru:
« Last Edit: March 21, 2013, 04:19:06 PM by FantaSTIc_04 »


1990 300zx Sold
2004 WRX Sti
2005 Rx300 Sold

Offline Pleiades

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  • 2005 FORESTER 2.5 XT TURBO
Re: P0420 Code Surviver!!!
« Reply #1 on: January 27, 2013, 08:19:45 PM »
Thank You  8)
Great tips for the unaware  ;)

If you only have a hammer, you tend to see every problem as a nail.

Offline MasterForce

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  • Posts: 477
Re: P0420 Code Surviver!!!
« Reply #2 on: January 28, 2013, 11:37:07 AM »
Also for those who use Cobb AP. Their MAPs "disable" the sensor. The sensor still needs to be plugged in though. I dont know if the code will still pop up for other reasons mention above though.
« Last Edit: January 28, 2013, 11:39:58 AM by MasterForce »
-'11 SWP STi Sedan *COBB SF Intake + Box *Invidia Catless DP *Invidia Dual Ti Q300
*SLOWtuned @ 213 AWHP - 93 FT-LB @ 20 PSI

-'11 Kawasaki Lime Green ZX-6R *M4 GP Slip-on

Offline FantaSTIc_04

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  • Posts: 51
  • 2004 Blue WRX Sti
Re: P0420 Code Surviver!!!
« Reply #3 on: January 30, 2013, 11:13:52 AM »
You're welcome. :)
Yeah the Cobb AP is a beast too, it can solve anything!  8)


1990 300zx Sold
2004 WRX Sti
2005 Rx300 Sold