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Discussion Starter #1
Hi guys,

Today my CEL came on.
I used a bluetooth OBD2 scanner and the OBDFusion app showed P0139 for the error code.

I pulled my records - I had the same code on Dec.2019. The code had gone on/off a few times, then finally my mechanic replaced the downstream sensor (Part #24647 NGK).
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Is it ok to clear the code with the app, or should I wait a couple days to see if it sorts itself out?
I figure I have a year warranty on the downstream O2 sensor (IF that's what the problem is), so that's good news.
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Not sure if related or imported but:
Cat.Converter replaced: Jan.2018
Maf sensor cleaned: March 2014.(90,000 km ago)
Upstream O2 sensor: original.
 

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The question is if the primary O2 sensor is working properly as well, what are the sft and lft?

You should be within +/- 8% total.



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Discussion Starter #4 (Edited)
@MrRangerZr1
Looks like aftermarket catalytic converter:
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Jan.10/2018
Replace faulty converter (AP direct fit 642189) Efficiency below threshold P0420

@greg1c
Hi Greg, with the OBDFusion app - would that tell me that information? Where would I look for that?
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Also, is it worth getting the PGM-FI software update, according to Service Bulletin 14-001?
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NOTE: It just went off after I got in the car this morning and started it.
So, that was less than 1/2 a day with the CEL light (P0139)

I'm sure it will be back.
 

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If your car fits in TSB 14-001 and you live in an area that requires A valid emmisions test for a tag, I would at least check to see if the update has been done and what the costs for the code upgrade may be. From what the TSB says it is .3 flat rate hours, not sure if there would be an additional charge besides the .3 hours .


As far as the the long term and short term fuel trims go they are available via the OBD port, reading on there web page it appears the software you have supports long term and short term fuel trims.

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I was curious about the TSB you guys are talking about, and I managed to find a copy. Just figure I'd attach it here for the future in case the link dies.

I had a similar code this year, but it was P0133 - A/F Sensor 1 Response Malfunction / B1S1 Slow Response.

I did a bunch of reading about it that didn't really go anywhere. I've only had that code once since owning the car, and it hasn't come back.

That PCM update looks like a good first step.
 

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Discussion Starter #7
If your car fits in TSB 14-001 and you live in an area that requires A valid emmisions test for a tag, I would at least check to see if the update has been done and what the costs for the code upgrade may be. From what the TSB says it is .3 flat rate hours, not sure if there would be an additional charge besides the .3 hours .


As far as the the long term and short term fuel trims go they are available via the OBD port, reading on there web page it appears the software you have supports long term and short term fuel trims.

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We don't require emissions tests anymore where I am and (knock on wood) the CEL went off less than 1/2 day later. If it comes back and stays on, then I suppose that software upgrade would be a good step to consider. The software upgrade looks like it depends on some particular version of another piece of software, so could be more expensive. I'll cross that road when I come to it.

I'll plug the OBDII sensor back in and see what I can gleam about this sft and lft data. They should be within +/- 8% of each other?
 

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The short term fuel trim is reset every time the car is turned off, the long term fuel trim is kept as the baseline. The 2 fuel trims are additive, if your LFT is +10% and your SFT is +5% your total fuel trim is +15%. The ECM learns and adjusts those values based mostly on the primary air fuel sensor.

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Discussion Starter #9
Well, P0139 has come back yesterday and remained on today.

Original O2 sensor replaced Dec.10/2019 - NGK
P0139 code came on/went off about 8 weeks ago.
P0139 came on again, yesterday.

Used an OBD2 reader to check values, if this means something to anyone:
7.81 short term fuel % trim bank 1
4.69 long term fuel % trim bank 1
(OBD2 reader used with car parked/engine off - should car be running?)

Fuel mileage - although not great, it's also winter (winter gas/snow tires/cooler weather). So I'm not noticing abnormal (for winter) fuel economy.
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I'm pretty sure I have some exhaust work to be looked at some point, mentioned to me ~ April 2020. Could that also trigger this P0139?
I'll give it a good Italian tune-up to see if that helps. I find sometimes this CEL will turn off about a good run.
 

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Are those fuel trim readings positive or negative?

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The ECM is adding 12%+ more fuel. So either you have a small vacuum leak, or a dirty MAF sensor or a dirty fuel injectors or fouled spark plug or weak coil. But something is driving the engine lean. Check the PCV and the o'rings on the dipstick. It would be a small leak. Possibly the intake hose from the throttle body to the air cleaner.

The p0139 is just a symptom of what is happening.



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Discussion Starter #13
@greg1c Thanks - I read that I should be checking the values, while the engine is running for a few minutes.
The values I provided you were with the engine off.
 

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Long term fuel trimsrapidly, and are kept after the key is turned off. Short term goes to 0 every time you start the engine.

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Those fuel trim numbers are very normal. You should be checking those numbers are the O2 sensor goes into closed loop mode with the catalytic converter fully heated up.
 

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Discussion Starter #16 (Edited)
@t-rd
Ok, I'll have to report back with those numbers when I get a chance. That was with the car off.
What's the best way for me to get appropriate readings?

I read further that I should have the car on and check those numbers:
1. @ idle for ~ 30 seconds, read values.
2. @ 1,500 rpm ~ same, read values.
3. @ 2,500 rpm ~ same, read values.

Does that seem like a good way to test.
Or, should I be going for a drive, with the scanner plugged in and then checking the numbers?

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Edit: The check engine light went off today, the first time I got in the car - turned key to acc - waited - light goes off, started car - went on my way and didn't come back on today. Knock on wood. So, something is on the borderline.
Lasted about 3 days this time - then went off. Approx.8 weeks ago, lasted for 1/2 day, then went off.
 

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Discussion Starter #17
This is hilarious - well not really.

The check engine light came on again today as I was driving home from running errands. (6 days after it last turned off).
P0139 again of course.

I'm setting an appointment with my mechanic to have this looked at. The frequency between each cel on/off event is decreasing.
That's 3x on/off within ~ 8 weeks.
 

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This is hilarious - well not really.

The check engine light came on again today as I was driving home from running errands. (6 days after it last turned off).
P0139 again of course.

I'm setting an appointment with my mechanic to have this looked at. The frequency between each cel on/off event is decreasing.
That's 3x on/off within ~ 8 weeks.
Most likely a failing O2 sensor.
 

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Mine has been randomly throwing P0139 for a couple of years now. Seems to be coming on when I really hammer it, then goes back off after 3 "normal/slow" cycles.

I replaced the downstream A/F sensor and upstream O2 over a year ago with Denso and it didn't change much at all. I had no idea about the TSB. If I still have the car this summer I'm going to get the TSB done. I'll gladly pay Honda to do this one, better than paying another $100+ for an A/F sensor or 200+ for a cat that isn't needed.
 

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@Marc999
Yes, your exhaust leak could cause this too. I'm speaking (or typing) from experience.
Also, this code will pop up usually in cold weather or when you go in a water puddle.

Cleaning the downstream O2 sensor could help, but you also need to fix that exhaust issue before the sensor packs up. Mine did.

In my case, P0139 would pop up and CEL would go off after about 2 hours highway driving, and wouldn't pop up again until after about 3 to 4 months. Sometimes with city driving, it goes off after about 3 days.
I could hear an exhaust leak with gear in Reverse, but neither I nor mechs could find it, so we couldn't fix it. B1S2 finally packed up (or so I'm thinking) after about 2years and 5 months. It now gives P0141. (sensor heater circuit). Sensor circuits and harness have been checked and are fine.
I would need to change sensor soon to protect my cat. but would also like to get that exhaust leak sorted.
Hope this helps.
 
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