SES Trouble
Thread Starter
Staging Lane
Joined: Mar 2013
Posts: 84
Likes: 0
From: Nor-Cal, CA
SES Trouble Hey guys, been having the ses light on and with scanned code p0420 which is bank one catalyst effiency. i've had this code for over two years and just a couple days ago the ses light turned off on its own. what could be going on? Prior to this i smogged the car two years ago and passed emissions but failed the test because the ses light came on (i had cleared codes and reset the light)..i just bought some cats and now dont know if i should replace at all. any ideas??
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
SES Trouble The catalyst efficiency test specifically tests the catalyst by sending a fueling step thru the engine and timing it from the front NBO2 to the rear NBO2... if the time is too short the test fails and sets P0420 or P0430 depending on the bank.
If the DTC cleared then the test passed for this one time or for now, but in the future it will probably fail again and again.
You can make the test pass always by introducing an small airleak at the rear NBO2, or by using an extender adapter to move the rear NBO2 out of the exhaust gas stream.
If you have replacement cats you may as well install them... you may need some studs/nuts (Dorman) and cat gaskets (GM).
If the DTC cleared then the test passed for this one time or for now, but in the future it will probably fail again and again.
You can make the test pass always by introducing an small airleak at the rear NBO2, or by using an extender adapter to move the rear NBO2 out of the exhaust gas stream.
If you have replacement cats you may as well install them... you may need some studs/nuts (Dorman) and cat gaskets (GM).
Last edited by joecar; May 26, 2016 at 11:44 PM.
Thread Starter
Staging Lane
Joined: Mar 2013
Posts: 84
Likes: 0
From: Nor-Cal, CA
Im gonna replace the drivers side. i just dont understand why the SES would turn off after a long time, its not the first time either. Still the drivers side cat is toast..just worried about readiness for smog
