OBDII says P420, O2 Sensor

[LaGrasta]

I hit AutoZone during my lunch break today, paid $70 and walked out with a new Bosch part. Should I just go ahead and replace it or try clearing the code first, double checking first? Could the code be a mistake and only need clearing?

BTW, I believe this is considered "right bank". Driver side above the cat.

[MountainManJoe]

according to Google ...

http://www.mr2.com/TEXT/O2_Sensor.html

testing in the vehicle...
[youtube]http://www.youtube.com/watch?v=KxhrCl3B22M[/youtube]

on the bench...
[youtube]http://www.youtube.com/watch?v=stFhLSHsOGg[/youtube]

[LaGrasta]

Read it and printed it, thank you.

After reading it, I'm starting to think the O2 may not be bad. I guess I'll disconnect the battery and force the computer to revaluate. If it still lights "Service Engine Soon", I'll test the O2.

I have 182,000 and the last time I tuned this up was at 129,000. It may just need new ignition parts, as stated in the write-up. I haven't noticed any needs however as far as performance.

I'll report back after I dabble with it this weekend.

[LiftedAWDAstro]

Generally a P0420 code is considered time to replace the catalytic converter. It is the code for converter inefficiency.

[LaGrasta]

I replaced the cats a few years back; was hoping to never have to again. When P420 was pulled up on the AutoZone computers, it said 02 and exactly which one as well. Hmmm.

[LaGrasta]

I hear what you're saying and I've explored further, but still haven't acted. I keep getting mixed stories. UGH!

[LiftedAWDAstro]

Here is some reading for you:

P0420 Code thread.

Another P0420 Code thread.

Before doing any more work, I would get the codes read again. I used this Actron Scanner to read the O2 sensors live while my truck was running to verify what O2 sensor was not functioning properly. I found one that read 1.250 V and then would read 0.000 V. When it was sort of working, it read 0.100 volts give or take a few milivolts. The new O2 sensor reads between 0.8 and 0.1 volts as I drove. This scanner is around $100 at auto parts stores but if you replace that downstream O2 sensor and still have to replace the converter after, you wasted almost the price of the scanner on a part you didn't need. It may cost more now but it will save you money in the future.

[LaGrasta]

thanks, sounds like good advice on the scanner. Stinks though, since I already own one. But a tool is not the same as the correct tool.

I'll give these new threads a read…

[LaGrasta]

Continued to ask around and went for a cat replacement. I replaced it an hour ago during my lunch, only $200 parts/labor. I'm not sure how the Service Engine Soon light goes off. I imagine during my 20 mile drive home tonight, it might reanalyze and clear itself.

[LiftedAWDAstro]

It should reset itself after a few drive cycles.

[LaGrasta]

It didn't go off after the drive home so I pulled the ECM fuse as well as disconnected the battery; none of which worked. I plugged the OBDII back in and sure enough, it's still throwing the P420 code.

Drove it again this morning and the light still glows. My hope is you're correct and I need only a few more drive cycles before it resets. If it doesn't, I remain asking what's causing it to light.

I learned a bit more about my OBD tester and it actually tells the full story, being able to read the individual O2 sensors and such. I'll monitor each sensor for the right millivolts this weekend if the light is still on.

I'll report back…

[LaGrasta]

hundreds of miles, still on. We're heading for a 1000+ miles trip this thursday. I guess the light will be on for the trip too.

[LaGrasta]

So funny.

I gave up on the cat replacement fixing the problem as the light hasn't gone off and the OBD still pulls the P420 code.

I went to lunch just now, just after my earlier post today and ran the scan again. Still the P420.

I gave up and planned to pick up the sensor I had already bought once, but returned for the left bank. No sooner had I said that to myself, I looked down at the dash and the light is OFF.

So funny.

[LiftedAWDAstro]

I bet you won't see the light again for the trip.

[LaGrasta]

Okay, no light during the 1000 mile journey. However each time I ran an OBD analysis, it still threw the P420 code. What gives? Do I still need the sensor?

BTW, MPG was 15.2 for the duration. I suspect this is partly inspite of my recent tranny rebuild, it still seems to get hung up in gear forcing me to let off the pedal a tad for it to down-shift.