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Diagnosing a failing catalytic converter


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My 01 Boxster S (70K miles) has starting throwing P0430 CEL codes. Through help from Porsche forums I have ruled out bad O2 sensors and other upstream stream systems causes. Before I investigate changing the pre-cat, I remember reading somewhere that with an infrared thermometer you can read the temp of the cat as compared to the manifold and determine if the cat is bad by the temperature differential. Has anyone done this and is it a good indicator to make the final decision to purchase a new cat? How much difference (higher) should the pre-cat be? Thanks

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My 01 Boxster S (70K miles) has starting throwing P0430 CEL codes. Through help from Porsche forums I have ruled out bad O2 sensors and other upstream stream systems causes. Before I investigate changing the pre-cat, I remember reading somewhere that with an infrared thermometer you can read the temp of the cat as compared to the manifold and determine if the cat is bad by the temperature differential. Has anyone done this and is it a good indicator to make the final decision to purchase a new cat? How much difference (higher) should the pre-cat be? Thanks

First of all, P0430 on your car is not the pre-cat, it is the larger main cat (called the "three way") on cylinder bank 4-6. Assuming you have tested the O2 sensors before and after the three way, and that they are in working order, the main cat should be running at greater than 386 C (727 F).

202-05.gif

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Be careful when testing using temp as you can be mislead and fail a working convertor. As a general rule of thumb, the outlet temp should be 50C higher then the inlet but there are many other factors to consider.

True enough, but a main cat that is running substantially colder than expected is usually a good sign of a problem with the cat. More often than not, when we see a P0430/0420, it traces to an O2 sensor issue more often than the cat itself, which is why I implied that the OP should be sure they check out before even bothering to check the cat temps.

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JFP, Thank you for the clarification regarding which ‘cat’ (pre cat or main cat converter) is failing when you get a P0430 code. The reason I stated the pre cat was based on the On Board Diagnostic information that I received from Form members indicating ……

from ON -BOARD DIAGNOSTIC for P0420 , P0430, "Note: In the case of a catalytic converter fault in the Boxster (2.7l and 3.2l), only the pre-catalytic converter is to be replaced ".

The note indicates the pre-catalytic converter to be replaced ???????

As for checking the operation of the O2 sensors (pre and post) below are the Durametric readings…

At idle and 180 degrees engine temp……….

BANK 1

Front O2 sensor voltage readings: 0.08 to 0.78 fluctuating (like roller coaster) resistance reading: 128 steady (flat line)

Rear O2 sensor voltage readings: 0.68 to 0.76 steady (flat line) resistance reading: 320 steady (flat line)

BANK 2

Front O2 sensor voltage readings: 0.09 to 0.78 fluctuating (like roller coaster) resistance reading: 64 steady (flat line)

Rear O2 sensor voltage readings: 0.65 to 0.79 steady (flat line) resistance reading: 192 steady (flat line)

All (4) O2 sensors heater voltage: 2.05 v

I understanding that these values/readings are normal and functioning. Any suggestions? Thanks.

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JFP, Thank you for the clarification regarding which ‘cat’ (pre cat or main cat converter) is failing when you get a P0430 code. The reason I stated the pre cat was based on the On Board Diagnostic information that I received from Form members indicating ……

from ON -BOARD DIAGNOSTIC for P0420 , P0430, "Note: In the case of a catalytic converter fault in the Boxster (2.7l and 3.2l), only the pre-catalytic converter is to be replaced ".

The note indicates the pre-catalytic converter to be replaced ???????

As for checking the operation of the O2 sensors (pre and post) below are the Durametric readings…

At idle and 180 degrees engine temp……….

BANK 1

Front O2 sensor voltage readings: 0.08 to 0.78 fluctuating (like roller coaster) resistance reading: 128 steady (flat line)

Rear O2 sensor voltage readings: 0.68 to 0.76 steady (flat line) resistance reading: 320 steady (flat line)

BANK 2

Front O2 sensor voltage readings: 0.09 to 0.78 fluctuating (like roller coaster) resistance reading: 64 steady (flat line)

Rear O2 sensor voltage readings: 0.65 to 0.79 steady (flat line) resistance reading: 192 steady (flat line)

All (4) O2 sensors heater voltage: 2.05 v

I understanding that these values/readings are normal and functioning. Any suggestions? Thanks.

Sorry but the OEM OBD II diagnostics manual for your car lists P0430 as "conversion too low on the three way", or main cat on cylinder bank 4-6 (bank #2), it is not the pre-cat. The OBD II manual's solution in the decision tree if code P0430 persists is "replace three way catalytic converter".

Try checking the main cat on bank #2 for temperature, if it is lower than exepected, you are in the market for a new three way on bank #2. You can also reverse the O2 sensors side for side to see if the code changes to a P0420, which would be the same issue, but now on bank #1, which would be indicative of a sensor issue rather than the cat itself. Be sure you test this thoroughly, because the three way is one very expensive part..............

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JFP, Thanks again for the clarification regarding the TWC (main cat infront of the muffler) bank 2 (drivers side). One other clarification please. In the diagram you provided, there are three 02 sensors shown. #26 [front of pre-cat], #27 [after pre-cat] & #25 [after main cat].

Which O2 sensors are present on my 01 S? Number 26 & 27 or 25 & 26 or 25 & 27? Thanks!

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If the problem turns out to follow the sensor, look to using the Bosch part with pigtail attached at the factory which is the appropriate length for the problem sensor.

My '01S passenger side front sensor got tired around 57k miles. About a year later, just for fun, I replaced the other front sensor. Seems those are the most common to fail so swap the fronts first from side to side as JFP suggests and see (hope) if the problem code shifts.

A table of cross-referenced O2 sensor part numbers is here.

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  • 2 weeks later...

I am troubleshooting a P0430 right now on a 2000 Boxster S. From the Bentley manual I thought that 2000-2004 had the O2 sensors before and after the header cat (26 & 27 in the pic above), with no sensor after the main big cat that is closer to the tailpipe. I have seen several vendors that state that you can remove the big cat with no CEL because there is no monitoring after that cat. I thought that the 97-99 were the only ones that had an O2 sensor after the big cat (since that was the only cat they had, they would have 25 & 27 in the pic above). I had a line on a replacement big cat but I told that person never mind because I thought I needed the header cat.

I have never looked under the car so I am only basing from what I have read, but I feel like Papa Klump: I'm confused.

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I am troubleshooting a P0430 right now on a 2000 Boxster S. From the Bentley manual I thought that 2000-2004 had the O2 sensors before and after the header cat (26 & 27 in the pic above), with no sensor after the main big cat that is closer to the tailpipe. I have seen several vendors that state that you can remove the big cat with no CEL because there is no monitoring after that cat. I thought that the 97-99 were the only ones that had an O2 sensor after the big cat (since that was the only cat they had, they would have 25 & 27 in the pic above). I had a line on a replacement big cat but I told that person never mind because I thought I needed the header cat.

I have never looked under the car so I am only basing from what I have read, but I feel like Papa Klump: I'm confused.

The cars came in multiple configurations between 1997 and 2004; some of the earliest US cars had only one cat (main three way) with sensors before and after it, then came the two cat version with sensors ahead and behind the precat, with none after the main cat (what you are describing). Then came the more conventional configuration with sensors ahead of the precat and behind the main cat. Add in the "RoW" (read non US) cars that only had one O2 sensor rather than two, and then in 2005 you get the US cars with two cats, one integrated into the side of the muffler assembly (red arrows below) just to confuse things even more:

Pic4.jpg

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  • 1 year later...

Resurrecting an old thread but, I have a similar situation. In my case (2001 S with tiptronic), I have the 26 and 27 sensors, so fore and aft the pre-cat. If the cat is indeed bad ( not sure yet), it would normally be the pre-cat, no? Since the sensors only seem to monitor this cat.

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Resurrecting an old thread but, I have a similar situation. In my case (2001 S with tiptronic), I have the 26 and 27 sensors, so fore and aft the pre-cat. If the cat is indeed bad ( not sure yet), it would normally be the pre-cat, no? Since the sensors only seem to monitor this cat.

 

Should be.

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