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Discussion Starter #1
I recently repaired the flexpipes, thinking that this would also stop my CEL from throwing out the following codes:
16519 - B1S1 heating circuit malfunction
16523 - B1S2 response too slow
16539 - B2S1 heating circuit malfunction
16543 - B2S2 response too slow

Unfortunately, they are still showing up. I have approx 165K miles on them.

Is it time to buy new? Or is there some common cause possibly affecting all 4 sensors that I should look at beforehand? If I do need new, any suggestions as to which brand to buy? I would prefer to get OEM replacements with the color-coded connectors.

Thanks.
 

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If over 100,000 miles, the sensors are suspect anyway - they don't last forever. I've needed replacements in the 150-200k range. That said, multiple heating circuit malfunctions seem...odd. Maybe a wiring issue?

I chose Bosch direct-fit sensors (not the splice-in type). Much more expensive than generic eBay [email protected], much less than original VW.
 

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Correct, after 100k miles the sensors are considered at life's end. Some people get lucky and they survive longer. But in general and per the service schedule, 100k miles is the time to replace them.

I'm in the same camp as scotts13, I've used the splice in type, but those don't always play nice.

Now, I just get the Bosch or NGK direct fit (with color coded plugs, black , green and brown) and I'm done.
The price of these sting a bit, but it's a much better deal than buying the Genuine Audi/VW. Your just paying for the four rings at that point.
 

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I replaced my flexpipe recently as well and I overheated one of the O2 sensors in the process because I had trouble removing the sensors with hand tools so I used propane for help. A new upstream O2 sensor was suggested by forum members and it solved the problem. Note downstream showed normal status in VCDS only after I replaced upstream, so I think upstream affects downstream (for all I know possibly the reverse as well). I have a V4 FWD, yours may need different sensor O2 models since it sounds like you have a V6.

If I were you I would follow the Audi diagnostic in the O2 thread I linked to. Then if no short is found I would replace just one upstream sensor and then see if that upstream and downstream read normal. Also when you remove the old sensors check them see how they look. Best of luck let us know what happens.
 

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Still, with all 4 showing codes, I would start checking the grounds on the car.
 

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Note downstream showed normal status in VCDS only after I replaced upstream, so I think upstream affects downstream (for all I know possibly the reverse as well).
The downstream O2 sensor only checks to make sure the upstream sensor is working properly. The downstream sensors have NO control over the emissions system. The only thing they do if they go bad or malfunction is throw the CEL and that's only because they aren't within the tolerance range coded into the ECU.
 

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A heating circuit code probably means a failed sensor, but it's easy to check.

The two same-color leads of the oxygen sensor are the heater leads. They should measure around 10 to 15 ohms between the two wires (unplugged, sensor side). If you don't get that, replace the sensor.
 
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