Scanner for looking at O2 functionality
Scanner for looking at O2 functionality I am looking for a scanner that I can watch my O2 sensors on. I have a code P0420 and replaced the rear sensor with a new denso O2 and it still came on. My smog test shows that the CAT is still functioning HC PPM were 10-15 so I dont think it is that. looking for the problem and figure this has to be the best place to start
Thanks
Jason
Thanks
Jason
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
P0420 indicates cat efficiency has failed... replacing the rear O2 sensor will not fix this.
The test for P0420 times the response of the rear O2 wrt the front O2 (to a step change in commanded AFR)... if the response time is too short then the test fails (P0420 or P0430 trigger).
If the front or rear O2's were not working then the cat test could never run.
Yes, 10-15 PPM are under the max limit for the 15mph/25mph test, but if the DTC is present then CA fails you.
P0420 or P0430
The test for P0420 times the response of the rear O2 wrt the front O2 (to a step change in commanded AFR)... if the response time is too short then the test fails (P0420 or P0430 trigger).
If the front or rear O2's were not working then the cat test could never run.
Yes, 10-15 PPM are under the max limit for the 15mph/25mph test, but if the DTC is present then CA fails you.
P0420 or P0430
So do you think it is actually the CAT? I just didnt want to throw parts at it. I have read that people have watched the O2 sensor in real time and made sure it was functioning correctly. Thanks
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
yes...
read the description of how the PCM performs the test ("Circuit Description" items 1 thru 5): P0420 or P0430
look at this pic, the time from 1 to 2 is too short, or the time from 3 to 4 is too short:
the vertical marker is where P0420 triggered (bank 1 cat failed);
bank 1: look at HO2S12 wrt HO2S11: the rear O2 responds too soon (jumps down at 2 , then jumps up at 4), this cat failed;
bank 2: look at HO2S22 wrt HO2S21: the rear O2 is almost not affected (barely dips only a little), this cat passed.
read the description of how the PCM performs the test ("Circuit Description" items 1 thru 5): P0420 or P0430
look at this pic, the time from 1 to 2 is too short, or the time from 3 to 4 is too short:
the vertical marker is where P0420 triggered (bank 1 cat failed);
bank 1: look at HO2S12 wrt HO2S11: the rear O2 responds too soon (jumps down at 2 , then jumps up at 4), this cat failed;
bank 2: look at HO2S22 wrt HO2S21: the rear O2 is almost not affected (barely dips only a little), this cat passed.
Last edited by joecar; Apr 16, 2013 at 06:53 PM.
