9 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHP0420 Catalytic Converter Low Efficiency
Leading reported evidence
Check o2 readings
Performed · outcome unconfirmed
No successful repair reported for this finding.
0
Reported fixes
0
Unsuccessful attempts
1
Discussions
Read evidence and context
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
I checked the O2 readings from my scanner and it looks like the after cat readings fluctuate a bit between .1 and .7 at about 2K rpm.
Leading evidence: 'Check o2 readings' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'car not heating up fully' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check o2 readings' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
Source reports, not a diagnosis or a success probability. Counts refer to discussions and can overlap.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Performed · outcome unconfirmed · Original poster
I reset the code, but now I can't get the catalyst converter test to complete.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that performed work without a confirmed outcome
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
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Performed · outcome unconfirmed · Original poster
At least now I have 2 years to pick up a good condition used cat.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that suspect a cause
1
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Suspected cause · Original poster
I've seen 10 on one short drive, but figured that was due to the car not heating up fully.
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
Discussions that contain suggestions
1
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0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suggestion · Original poster
I'd like to catch any issues before replacing the cats and potentially fouling them again.
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
9 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261027T075545Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
I recently purchased a 2003 996 C2. It has 155K miles and about 113K miles on a big bearing factory replacement engine that was Porsche dealer replaced in 2007 at 42K miles.
I was driving along and got a check engine light. Pulling the codes I got a P0420, catalytic converter low efficiency. I reset the code, but now I can't get the catalyst converter test to complete. Normally, I wouldn't care that much, but since I just purchased the car from out of state I need to pass MD smog test by the end of March.
I checked the O2 readings from my scanner and it looks like the after cat readings fluctuate a bit between .1 and .7 at about 2K rpm. They stay pretty stable at .5-.7 when the car is sitting at idle. From reading online it seems like these numbers are a bit on the edge. Meaning my cats may be bad. The car drives perfectly fine. The idle sometimes seems a bit rough, but I think that's mostly due to the bad motor mounts. I have new mounts on the way. Driving and revving the car is perfectly smooth, no stumbling and good power.
Since I wasn't able to get the full service history, I also have new plugs and coil packs on the way. The coil packs look original, I can't imagine the plugs are, but definitely not sure when they were replaced.
Any chance new plugs may take care of the problem, or does P0420 really fully point to bad cats? And if the cats are bad anyone know if I can use the 49 state cats and still keep the check engine light happy? They're A LOT cheaper than aftermarket or OEM CARB cats by a huge margin.
Thanks in advance!
Car is due for cats if they have 170k. You can usually find some low mileage ones on eBay that are original. Super easy to install too. Plugs and coils and resetting isn't going to fix this. Cats on these are usually stout, high mileage and the blow by or rich conditions will kill cats eventually. I would go to eBay. Or maybe you can get replacement high flow cats that don't need certification for Maryland like they do for California? That could work too.
Will the 200 cell/high flow/49 state cats pass the cars OBD catalyst test? I've read that they sometimes won't pass the cars catalyst test. Maryland doesn't do the sniff test for 2003's, which I heard most cats will easily pass. MD reads it through the OBD port and if the catalyst test says incomplete they fail you.
Should I be concerned the cats went out at 155k? Or is that about what I should expect out of the cats? My LT fuel trims ranges from 3-7 on most drives. I've seen 10 on one short drive, but figured that was due to the car not heating up fully. I'd like to catch any issues before replacing the cats and potentially fouling them again.
Thanks again!
The records I have show rear O2 sensors replaced at 71K miles. I'll be picking up additional records this coming week, so maybe the front ones were replaced. Once I put new cats in, I'll probably put new O2 sensors in as well.
Thanks!
Just wanted to finish this thread out for anyone else in the same situation. I was able to pass MD emissions inspection with only the catalyst test listed as not ready. In MD you can have either the catalyst or evaporative monitor, but not both, not ready. From reading online it seems a few other states are that way as well.
At least now I have 2 years to pick up a good condition used cat.
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