O2 sensor codes already replaced sensors

2004 Carrera 2 all factory exhaust and everything. I just had 3 codes pop back up after I have already replaced my downstream sensors with new Bosch units: P0156: Porsche fault code 23 - O2 sensor ageing behind cat c. bank 2 P0139: Porsche fault code 17 - O2 sensor ageing behind cat c. bank 1 P2098: Porsche fault code 22 - O2 sensor ageing delay bank 2 I had replaced both my downstream sensors with new bosch units about a month ago, cleared the same codes and went on my way, but they have popped up again. Is there something else that I need to do to reset the age of my sensors....and can I do it from a durametric pro?

I recall something about a DME re-programming for certain 996.2's related to false O2 sensor codes. Not sure if your car falls into the VIN range, but it might be worth checking into. Other things to check are exhaust leaks or vacuum leaks. You can also try a hard reset by disconnecting you battery negative cable for 10 mins.

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Introduction of the new DME software on Jan. 12, 2004, as of the following VINs: 99 54S 62 1761 USA; 99 94S 65 1984 USA; and 99 84S 63 5157 USA [1] Full Article If it's already applied, I pulled some snippets of the information displayed to by Googles Gemini AI from its more long winded information. [Query: "the following porsche error codes still exist after o2 sensor replacement in attempt to correct the same error codes. P0156: Porsche fault code 23 - O2 sensor ageing behind cat c. bank 2 P0139: Porsche fault code 17 - O2 sensor ageing behind cat c. bank 1 P2098: Porsche fault code 22 - O2 sensor ageing delay bank 2" Static sensor tests can be done with a multimeter set to measure the resistance between the heaters (white wires on the sensor connection to the engine compartment connection to the DME) and should read within 3 to 3.5 ohms. The test I know for certain works, I can't vouch for the following. IMHO it appears as if this information may be correct. Take it with a grain of salt. Starting with the highest probability: Exhaust Leaks: [i] Inspect the areas around the input and output of the sensor for small cracks or tiny openings that might exist. Cause and Effect: Small cracks or loose flanges near the catalytic converter draw outside oxygen into the exhaust stream. This skews the sensor readings and slows down its voltage response. Fix: Get these areas corrected. Replace or repair as needed. Front Sensors: Post sensors are good. Cause and effect? The DME calculates downstream delay by comparing it to the upstream (Sensor 1) data. If the pre-cat sensors are old/slow, it ruins the math. Check the age of your upstream oxygen sensors. If they have never been replaced, they may be forcing the downstream sensors out of sync. Vacuum or intake leaks: Unmetered air entering the engine shifts the overall fuel trims. The DME tries to compensate, pushing the post-cat sensor voltages to extreme limits where they respond sluggishly. Monitor long-term fuel trims (LTFT) with a scanner. If trims are heavily positive at idle, look for a cracked vacuum line or an oil separator (AOS) leak.

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Hero stuff right here. I already went through for exhaust leaks, but my upstream sensors definitely aren't new so I guess that is the next thing I'll take a swing at!

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Dunno about the hero stuff. I have an O2 issue causing a CEL light I have been chasing down since March. In my situation, all 4 sensors had been replaced in an effort to fix the CEL, but the two post sensors continued to show the same display codes and the CEL was not resolved. I found a mouses nest in my rear electronics where the DME was. This led to verifying that the wiring was good. I didn't see any damage to the wiring around the nest or DME, but it never hurts to check. That's how I know about the static O2 testing. I went to the dealer for an inspection on it. They reported it was a DME ground fault. I sent my DME into ECU Doctors (whom I would highly recommend due to their diligence in keeping me updated. Not to mention they could clone a spare master since the immobilizer also has to go with it). The DME tested good, no faults. At this point I queried Gemini AI as to other possibilities. It said to the check the vehicle ground points (GP12, 8 and 9), and that a faulty ground could cause the exact errors. Another mention was the relay labeled #2 on relay panel two may also be an issue. I ran a test on the relay from the information and found it was not activating. I should hear it switch. I replaced it last evening while today I'm checking GP8 and GP9. The DME should arrive back tomorrow and I'll reset the codes and hope I've eliminated the issue. If not, then it's time for a 'Hail Mary' and put spacers in as some recommended. The dealers estimate for repair was from $3,500 to $5,000 to fix it and they'd apply the $980 inspection fee to it. I'll take it our local Indy shop.