P0420 Without mods... Why?
Thread Starter
Joined: Sep 2008
Posts: 11
From: Utah
P0420 Without mods... Why?
I have a 2008 Pony Package Mustang I bought new back in (you guessed it) '08. It has aprox. 24000 miles and is 100% stock (well except for wheels...
).
ANYWAY, a while back the check engine light came on with code P0420. I was going to have it checked, but after a few days the light went out. Now it's back... to stay. Now, I did the search but couldn't find a single P0420 code without something being modified, so my question to you esteemed gentlemen is: What is the most common cause for this code? Is it the O2 sensor, plugs, or something else? In other words, what should I do first to figure out what's causing this...
By the way, the car runs great, no issues what so ever... well, except for the check engine light...
Thank you for your help!!!
). ANYWAY, a while back the check engine light came on with code P0420. I was going to have it checked, but after a few days the light went out. Now it's back... to stay. Now, I did the search but couldn't find a single P0420 code without something being modified, so my question to you esteemed gentlemen is: What is the most common cause for this code? Is it the O2 sensor, plugs, or something else? In other words, what should I do first to figure out what's causing this...
By the way, the car runs great, no issues what so ever... well, except for the check engine light...
Thank you for your help!!!
4th Gear Member
Joined: Dec 2010
Posts: 1,597
From: Gallifrey
http://iihs.net/fsm/?dir=10&viewfile=Diagnostic%20Trouble%20Code%20(DT C)%20Charts%20and%20Descriptions.pdf
As it came on, went away, then came back...My guess would be a sensor. Pull 'em, test, and clean?
Code:
P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Description: Indicates the bank 1 catalyst system efficiency is below the acceptable threshold. Possible Causes: Use of leaded fuel Damaged heated oxygen sensor (HO2S) Out of range engine coolant temperature (ECT) sensor High fuel pressure Damaged exhaust manifold Damaged catalytic converter Oil contamination Cylinder misfiring Downstream HO2S wires improperly connected Damaged exhaust system pipe Damaged muffler/tailpipe assembly Retarded spark timing Leaking fuel injector Diagnostic Aids: Compare HO2S upstream HO2S11 and downstream HO2S12 switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increased amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set.
Last edited by wayne613; Jul 31, 2012 at 03:45 PM.
4th Gear Member
Joined: Dec 2010
Posts: 1,597
From: Gallifrey
So long as the wiring or connections are not in question, as jpplaw stated, it has to be a sensor or the cats themselves, since it's basically doing a comparison. Once it can't see xxxx difference it throws that DTC.
Last edited by wayne613; Jul 31, 2012 at 04:02 PM.
4th Gear Member
Joined: Dec 2010
Posts: 1,597
From: Gallifrey
Np.
Should you have a tuner, you may wish to monitor the cat temp, and a few other things.
http://iihs.net/fsm/?dir=237&viewfil....0L%20SOHC.pdf
Should you have a tuner, you may wish to monitor the cat temp, and a few other things.
http://iihs.net/fsm/?dir=237&viewfil....0L%20SOHC.pdf
5th Gear Member
Joined: May 2007
Posts: 2,388
From: Central Texas
I'd try the sensors first (you can swap them). Clear your codes, and see what happens after a dew days. If the 420 code eventually comes up after a few drive cycles, your passenger side cat is probably bad. If the code changes to p0430, the sensor is bad.