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P0133 & P1275 on '01 Boxster S

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I was hoping someone with more knowledge can assist me in interpreting some OBD II codes. I have a 2001 Boxster S which I purchased about 60 days ago. The car appeared to be very well taken care of and the PPI only found minor wear and tear items which I had fixed within a couple weeks of purchase. The car was approaching 45,000 miles so I also had the 45K service completed a couple weeks ago.

Last week while driving on my normal commute the CEL came on (steady burn). Since I had just had the 45K service completed at the dealership, I took it back to them and asked them to do a quick diagnostic. They came back with codes of P0133 & P1275 (Both of which I understand are the pre-cat O2 sensor on the bank 1). The dealership kept the car for the day and replaced the bank 1 pre-cat O2 sensor with a "scrap" sensor they had and the graph from the computer printout showed a similar wave pattern, to the one prior to installing the "scrap" sensor, with the delayed reading from the pre-cat sensor. The dealer's diagnosis was that the catalytic converter was bad on bank 1 (BTW is bank 1 the driver or passenger side on the 986?) and that it needed replaced. Since I do not have the funds to replace the catalytic converter at this time, I brought the car home and put it the garage to sit for awhile.

Based on everything I have been able to research the diagnostic jump to a bad catalytic converter seems a bit extreme. I don't understand how the wave form from the pre-cat O2 sensor is driving a diagnosis of a bad catalytic converter. I would have thought the only way to say the catalytic converter was bad would be to have some reading off of the post-cat O2 sensor. Based on my interpretation of the wave form and current status of the car (i.e. no loss of power), I do not believe the catalytic converter is plugged (i.e. there seems to be no air flow restriction that I can detect).

Am I off base here or should I continue to troubleshoot this beyond just replacing the catalytic converter?

Any thoughts or ideas would be appreciated.



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P0133 Signal Period for Oxygen Sensor Ageing, Bank 1 – Above/Below Limit

Possible causes:

– Oxygen sensor ahead of TWC

– Wiring (oxygen sensors exchanged)

P1275 Signal Delay Time for Oxygen Sensor Ageing, Bank 1 – Above/Below Limit

Possible causes:

– Oxygen sensor ahead of TWC

– Leak ahead of TWC or in the area of the oxygen sensor after TWC

– Wiring (oxygen sensors exchanged)

Looks like a bad O2 sensor ahead of the cat on bank 1 - or a bad connection.

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I went through pretty much the same thing your going through about six months ago. While driving home from just having my IMS and RMS changed out my CEL came on and the codes indicated bad 02 sensors and cats. I was told to replace 02 sensors and cats (very expensive), I had the car smoke tested three times and was told the rubber bellows on the secondary air system vacuum tank was bad. It was replaced but only half the codes went away. I was then told the secondary air system had to be replaced because it wasn't working ($800). Here's what I learned from all this, emission codes are only guidelines that tell you that you have an air fuel mixture that is not within parameters that meet established emission laws for the state you are living in at the time of manufacture. An example is the 02 sensor which everyone wants to replace once a code comes up that points to it. Reality may be that the code is pointing to the 02 sensor because the 02 sensor is telling the ECM that it "smells" something different than what it was programed to "smell." The ECM then adjusts air fuel mixture to compensate for what the 02 is smelling by either enrichment of fuel mixture or leaning out fuel mixture. The ECM can only do this by a certain percent and after so many cycles of this mixture the CEL comes on. Because it is difficult to determine the exact cause of the variation many mechanics will "shotgun" your repair by telling you that an entire system has to be replaced when actually it may be something minor. After having my car smoke tested three times the actual cause of my codes was found and replace. The cause- a $.25 cent vacuum hose had come undone from one of the diaphragms under the intake manifold in the secondary air system. So instead of thousands of dollars to repair it was only a couple of hundred and I still have the same 02 sensors and cats. Find yourself a good independent mechanic who has good diagnostic skills and let him have a go at it, that is what I did and it saved me a bundle in the long run.

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