I am having a similar issue...

First time so I will probably clear and monitor.

That said, it looks like the codes suggest a bad O2 sensor.
Is there more to it than that?

P0139 - Aging of O2 sensor behind the 3-way converter (cyls 1-3).

P1117 - O2 sensor heating bank 1 behind the 3-way converter.

I'd say a bad sensor is a pretty good WAG.

How many miles? If " a lot " you might just throw 2 new sensors in and stand back. I'd replace both if there are a good number of miles on the car and the sensors so both sensors start out "equal".

If the sensors are old, they most likely need to be replaced.

If not then you swap the one with the error with one without the error and see if the error moves with the sensor. When doing that test it's better two swap the front with the back (as opposed to side-to-side) since -- as Marc suggests -- the one on the opposite side is likely also on its last legs.

interchangeable. The leads are different lengths.

Swapping from side to side is ok. The other sensor while it is of the same age and so on is not manifesting any error and it is a shade tree test to "confirm" the suspected sensor is bad and the error is not due to something else.

There's always the risk of damaging the "good" sensor though. And with older cars the less use the connectors get subjected to the better I like it.

The lead lengths are different. The sensors and connectors are as best I can tell identical.

and in my experience the lead lengths are the same.

Part # 986.606.126.00 (2.5 1997)
Part # 986.606.126.01 (2.5 1998-1999)
Part # 986.606.126.01 (2.7/3.4 2000-2002)
Part # 986.606.226.00 (2.7/3.4 2003-2004)

were swappable the lead lengths were different. I can't recall which was which now but I do remember while I got them swapped the wiring could not be routed the usual way, through the grommets. No way I would run the wiring like it ended up as it would have worn through in no time. This was back in 2004 when I was having sensor issues.

'bout all I think of is Porsche changed the part numbers, elected to use sensors with the longer leads at all 4 corners to eliminate the sensors with the shorter leads to cut down on parts inventory.

They may have changed but the part numbers and equivalent Bosch parts (cheaper) are at the end of this

The car has around 60K.

If the code comes back, I will swap the sensors. that seems to make good sense.

If I am going to replace either of them, it makes sense to change them both at the same time.

That said, 60k seems a little early to start having problems. As a result, I am a little concerned that it might be something other than the O2 sensor

Boxster O2 sensor replacement

Click on any of the images for a larger version.

Based on the errors it would appear the heating element circuit has failed. The heating element is I think the most fragile of the two circuits of the sensor.

While above in an earlier post I did say swapping sensors side to side is ok, what I meant is it is ok in the sense it is better than swapping them front to back and vice versa, but I really do not like messing with the sensors much and the electrical connector which is part of the harness even less.

My recommendation would be to replace both sensors with new sensors but very carefully and worry about further diagnostics if the new sensors fail to quell the error codes.

I have been running since Thurs with the cleared codes. Nothing.

It might be that the IM readiness stuff is still playing out, but whatever it is, it is not condition critical.

But I want to be clear, these codes are suggestive of O2 problems and nothing else? The sensors are clearly the most obviousl thing, but since they are like $100, I don't want to be just throwing parts at a problem.

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JMstamford,ct
I have been running since Thurs with the cleared codes. Nothing.

It might be that the IM readiness stuff is still playing out, but whatever it is, it is not condition critical.

But I want to be clear, these codes are suggestive of O2 problems and nothing else? The sensors are clearly the most obviousl thing, but since they are like $100, I don't want to be just throwing parts at a problem.

Well, then pay $150/hour for a diagnosis and then pay for the sensors.

In one of my sources for P0139 -- O2 sensor value does not change between rich or lean -- the only cause listed is "oxygen sensor".

Diagnostic conditions:
RPMs betwen 720 aNd 2400.
Engine load between 0.8 and 2.6 ms.
O2 sensor heating active.
Oxygen sensing ahead of the converter active.
Calculated converter temperature above 665F.
No fuel tank ventilation.
No faults detected for fuel tank ventilation and secondary air injection system.

Test: Road test vehicle. Erase DTC memory.

Heat the O2 sensors (road test vehicle under load), run the engine at high RPM with no load).

Perform short test during the diagnostic conditions can be reached.

Read DTC memory.

You can of course elect to continue to drive the car until such time as you are convinced it is the sensors or someone points you to another possible explanation. I'd offer one but my sources do not offer anything else.

Check that: With the P1117 DTC, possible causes are: contact resistance, heating resistance too high, interruption in the heating circuits, interruption in the sensor signal wire, short circuit to plus. There are some electrical tests but they all involve testing the sensor and its circuits and connector.

But I think you answered my question. All points DO seem to lead to a bad (or going bad) O2 sensor.

not that you're throwing money at the problem, but at the solution.

As reported last time, I cleared the code and drove. I wanted to see if the car just threw a random code. I have since passed inspection etc. I have not been using the car very heavily due to a (now resolved) hip replacement. But it has been at least a few thousand miles and about a year and a half.

The return of the code is certainly suggestive that the sensor is, indeed failing. But apparently it is dying a VERY slow death. I am going to do the same as last time. Clear the code and see what happens.

If the code returns again, I will have to replace the sensor and I will likely replace both sides at the same time. I have seen it written that changing both is not necessary, but I am less than convinced.

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JMstamford,ct
As reported last time, I cleared the code and drove. I wanted to see if the car just threw a random code. I have since passed inspection etc. I have not been using the car very heavily due to a (now resolved) hip replacement. But it has been at least a few thousand miles and about a year and a half.

The return of the code is certainly suggestive that the sensor is, indeed failing. But apparently it is dying a VERY slow death. I am going to do the same as last time. Clear the code and see what happens.

If the code returns again, I will have to replace the sensor and I will likely replace both sides at the same time. I have seen it written that changing both is not necessary, but I am less than convinced.

O2 sensors can take some time to "die" or they can "die" right away, well, that is after some miles.

My previous experience with what proved to be bad sensors, at least one sensor, was the sensor failure was intermittent.

I wanted to catch the thing in the act but it took a while before I had a good sense of when it was going to fail to finally have at hand the OBD2 code reader/data viewer and could observe the sensor voltage values. The values were wrong but not as wrong as I had hoped. It was clear from the readings why the CEL took so long to appear. The sensor was working, just not very well.

More recently on the return leg of a trip I took to the midwest last Dec./Jan. my 996 generated an O2 sensor error, I forget the number now, but it pointed to the heating element of a sensor. I cleared the code at the station - a Shell station in Barstow, CA (might mention this was after having driven from Joplin MO over the span of 2 days or so) -- then drove on. I stopped someplace on I-5 and the CEL came on upon engine start after fueling. Same error code. I cleared it and drove on. Another stop for fuel and another CEL and the same code.

The failure was quite solid. At around 132K miles on the original sensors I just had all 4 replaced. A day's shakedown and I had the car in for its smog check which it passed with flying colors. The CEL has been dark ever since. As a bonus in this case -- but not the previous times I have replaced sensors in my Boxster -- the engine perked up some after the sensor change out.

It is up to you. You can continue to drive the car and put up with the intermittent CEL and sensor error code or you can have the indicated sensor replaced, and at 60K miles I would argue its counterpart on the other side should be replaced too.

I would lean towards the latter. For, ahhh, science I continued to drive my Boxster with a bad (though intermittently so) sensor but with the 996 science was involved. As soon as I could get the car in for new sensors I did so. Sure, I was under pressure to get the car smog checked -- it was past due -- but I would have had these replaced right away anyway.

And in the future if the Boxster sensors indicate a problem I'm just going to have the sensors replaced.

Is that suggestive of a wiring problem rather than a sensor problem?

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JMstamford,ct
Is that suggestive of a wiring problem rather than a sensor problem?

with the error condition absent the light is cleared and the error code is erased. I had this happen a few times with the converter fault I put up with for a couple of years. It might have cleared itself more often but almost every time I read the code and cleared the error so the DME didn't have time to clear it on its own.

"A mile of highway will take you one mile. A mile of runway will take you anywhere."

which to some extent is a good thing.

So 5 yrs ago and 3 yrs ago I just cleared the code and waited. No recurrence of the CEL for years (obviously). In the interim, I passed several inspections without issue and the car has run flawlessly - at least to my observation.

I am going to do the same as I have done before - clear the code and wait. I am thinking this is an intermittent electrical gremlin and the sensor is just fine. But only one way to find out....

On a more depressing note - this thread demonstrates that I only put 22K miles on the car in around 5 years. In fairness, there was a two year loss of usage due to injury. But still, 6-8K a year is not enough.
The car is now my mostly daily driver. Exception for snow/salt condition. It is harder on the car because my commute is only 5 miles - barely enough time to warm water much less oil.
I make a point to drive a distance at least once per month. Put 150 miles just today.
But sheesh.....

I get a recurring CEL for aging sensors. I have replaced all 4 O2 sensors and cleared the code several times. I have trouble getting readiness on SA and catalyst. This time catalyst is not ready. I have a year before my next smog check. I know how to get immediate readiness for the smog check, but don't want to do it unless I am going in for the check. I am sure the CEL will resurface. Car runs great. '00 S.

If there was only 1 code thrown, it would be 0133.

Tony

If the O2 sensors were replaced with the correct parts and the wires and connectors are ok and plugged in properly then it's likely a leak before the sensor. But I would check all of these things.

Have you had the headers off? It's also possible (but unlikely) that the O2 sensor was damaged during installation. You can swap sensors to see if the problem moves.

FWIW, both of those codes point to the same O2 sensor (passenger side, before O2 sensor) so you can focus on that area.