An 02 Sensor Mystery

H

hubertron

New member
Here is a really interesting one for the T4R community...

I live in Denver, CO and my check engine light goes off at 3 different places around town, but only those locations. Never anywhere else.

When I check the code its always 0430, Passenger side downstream 02 sensor.

I figured that maybe its just those area's are more polluted and my 02 sensor was going bad. So I switch the left and right 02 sensors. Figuring if its going bad, I will now throw a 0420 and know I need to get the sensor.

Well it turns out even with the swap, the same 0430 gets thrown at the same 3 locations. So I figured maybe my cat is bad, but I went to get my emissions test done thinking of course I am going to fail, but I just passed with pretty good figures:

HC GPM 0.0422 / 1.2 limit
CO GPM 2.4 / 15 limit
CO2 GPM 557.4
NOx GPM 0.02 / 2 limit

Which makes me think the cat is still good.

Does anyone have any idea what it could be?

- Spark plugs are only 3 years old and not a lot of miles in that time.
- Air filter is good, and looks well sealed
- Never got the driver side code
- Fuel milage is a bit down, but could just be chance

This is killing me, since I drive past one of those 3 places every few days!
 
Register to hide this ad
Curious. Post the 3 locations that seem to trigger the error so others in Denver can drive by and see what happens.
 
Well P0430 is a catalyst efficiency code... Though you're right in that the downstream is looking for changes in the oxygen storage capability to determine if the catalyst is failing or not.

I'd be curious what the freeze frame data shows and what the Mode$06 data shows for the Catalyst Efficiency Monitor test results.

It's possible that the front O2/AFR sensor might also be failing/faulty causing the rear to skew, but usually it's a different DTC that trips for that issue.
 
hubertron said:
I'll do 2,

1 - Eastbound I-70 just past Wadsworth
2 - Westbound 36 just coming out of Boulder but before Baseline
Click to expand...

1. Drive that often often, no issues.
2. Haven't been for a couple months but no issues.

Still strange you do though.
 
BlackWorksInc said:
Well P0430 is a catalyst efficiency code... Though you're right in that the downstream is looking for changes in the oxygen storage capability to determine if the catalyst is failing or not.

I'd be curious what the freeze frame data shows and what the Mode$06 data shows for the Catalyst Efficiency Monitor test results.

It's possible that the front O2/AFR sensor might also be failing/faulty causing the rear to skew, but usually it's a different DTC that trips for that issue.
Click to expand...



I agree with BlackWorks. Freeze frame and Mode06 data would help. I have seen the front O2/AFR sensor on some toyotas start to get slow and actually trip the cat code while never setting a code for the front sensor


Sent from my iPhone using Tapatalk
 
Jefe13 said:
I agree with BlackWorks. Freeze frame and Mode06 data would help. I have seen the front O2/AFR sensor on some toyotas start to get slow and actually trip the cat code while never setting a code for the front sensor


Sent from my iPhone using Tapatalk
Click to expand...

Even better they'll sometimes cause a weird voltage code for the rear O2 and changing that rear O2 won't fix it (just ask me how I know :P )
 
Jefe13 said:
HA! How long and how many sensors did it take to chase that down[emoji13]


Sent from my iPhone using Tapatalk
Click to expand...

I put one sensor in a 1st gen Tundra and it came back for the same DTC after a week or so. A coworker mentioned it to me and I spent the next hour or so scouring the datalists and checking all the tests in the FSM trying to find some indicator of the front AFR sensor failing/causing the issue.

I found nothing, not a damn thing that would lead me or anyone else to believe that the AFR was influencing the rear O2 DTC or in fact that either sensor was acting up. The rough conclusion I came to is that somewhere in the ECM logic it sees something in the front AFR for a period of time smaller than I could see (though to be honest I didn't scope it, I didn't have THAT much time on my hands, even though it was a slow day that day lol) and it thinks the rear O2 sensor is at fault. There's even a TSB for that issue on some vehicles but realistically none of the testing it vaguely references actually helps.

So really that's one of those things where it's like, "oh that DTC? throw a front AFR sensor in it because it just fixes it most of the time... why I don't know, it just does." Which honestly is infuriating for me as a technician because no matter how I tested it, there was no indication of failure or even pointing to the front AFR; but a new one fixed it. How the hell am I supposed to explain that to a customer if they ask me? lol
 
Last edited:
I live in the Ft. Collins area and I had the same codes. 0420 most of the time but sometimes 0430. I think the cat under the driver seat is bad. I reset the CEL and passed the emissions test no problem. Those codes come in when the catalyst efficiency has dropped below 95%. Still well within State limits apparently.
 
Some great responses!

Some updates. Last night I cleaned the MAF sensor. It really needed it. I haven't cleaned it since a 4wheel trip around White Rim in Utah last fall. Which is dumb on my part.

This morning the 0430 code trips in a new spot, going 30 MPH. It's never gone off at that speed or in that location. So I am thinking the computer is just adjusting. The idle was much better though, so at least an improvement there.

Tonight I am going clean the throttle body as well. There is no way that's not dirty based on how the MAF looked. It might not help with the code, but it certainly won't hurt.

I also got one of those fancy bluetooth OBDII sensors on its way from Amazon so I can get some logs of actual voltage data. I will post those here, when I figure out how to use it and have the code trip again.

Hopefully that might lead to the upstream sensors that BlackWorks, and Jefe mentioned. I would be overjoyed if it was just replacing some sensors vs replacing a cat.

Thanks so much for the responses!
 
Last edited:
I can't recall if Mode 6 data is stored from a Pending or confirmed DTC. It appears that your catalyst monitor isn't COMPLETE yet. That maybe why your Mode 6 data is missing for the Catalyst Bank 2 result. Did you clear codes before your drive?
 
Last edited:
Yep.

Cleared codes, drove, exported the above report.

On the commute home tonight, it should actually trigger the CEL, since I drive past that same area.
 
Lean Short Term but Rich Long Term
0x06 Short term fuel % trim - Bank 1 0.78 %
0x07 Long term fuel % trim - Bank 1 3.91 %
0x08 Short term fuel % trim - Bank 2 -4.69 %
0x09 Long term fuel % trim - Bank 2 6.25 %

I'm at a loss.
 
hubertron said:
Yep.

Cleared codes, drove, exported the above report.

On the commute home tonight, it should actually trigger the CEL, since I drive past that same area.
Click to expand...

How about a different approach on these spots that trigger the codes? How about mileage from your starting point to each of them. I'm wondering if that might tell something.
 
CXS said:
How about a different approach on these spots that trigger the codes? How about mileage from your starting point to each of them. I'm wondering if that might tell something.
Click to expand...

It seems like its after the engine is warmed up on local roads and then I get on a highway.

Like the transition from a warmed engine on local roads, to a warmed engine on the highway is causing issues somehow.

If I get on a highway when not warmed up, no problem.
 
LT on Bank 2 is within acceptable limits, most technicians won't even bat an eyelash at anything under 10%

Do you happen to have "Total Fuel Trim" on your scantool as well?
 
You must log in or register to reply here.

Members online

No members online now.
Total: 205 (members: 0, guests: 205)

Forum statistics

Threads
278,309
Messages
3,554,071
Members
248,016
Latest member
Advally Service

Share this page

Trending content

Back
Top