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Forum LockedCan I bypass secondary O2 sensor on W8

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Geofwil View Drop Down
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  Quote Geofwil Quote  Post ReplyReply Direct Link To This Post Topic: Can I bypass secondary O2 sensor on W8
    Posted: 13-Mar-2010 at 01:17
I have a fault code Catalyst system bank 2 efficiency below threshold. I have 210000 kms up and it could well be the cats. But I do not care just want the ECU light not to keep coming on. There are no serious emissions laws in NZ so is it possible to trick the ECU into thinking the cats are OK. I would rather not replace the cats as it will cost me more than the car is worth, about $9,000!!!!
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Majorn View Drop Down
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  Quote Majorn Quote  Post ReplyReply Direct Link To This Post Posted: 13-Mar-2010 at 09:55
I have the same problem, the car is emissiontested every year without any problems, but I get fault codes on the secondary sensors, so your cats might still work.
I read that GTI owners that change the downpipe get the same fault code, and some get some value changed while chipping the car so the code doesn't trigger a light.

Not shure if they do on our cars doe, I don't get a CEL at the same time as I get the fault code, I get it when the readiness codes has desided that the Secondary Air Injection system isn't working, but that might be triggered by sensor code.
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 14-Mar-2010 at 17:12
Likely cause is old downstream O2 sensors.

You can band-aid fix them by shunting a diode of the proper size in parallel with them, but you really should replace them. Search the Passat World forums for info on dioding them. Only works on the rear ones. The front are wide-band, 5-wire sensor units... cool, but pretty unique to our engine, and not cheap. The rears can be replaced with a standard Bosch 4-wire unit to save a dime or two.
'03 W8 Sedan 6MT     ..."it goes to 11!"
'02 V6 Wagon 4Mo 5MT (Swap In Work)     ...both black on black w/ limo tint
'14 JSW TDI 6MT
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Geofwil View Drop Down
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  Quote Geofwil Quote  Post ReplyReply Direct Link To This Post Posted: 14-Mar-2010 at 18:47
Thanks for that guys I am not adverse to replacing the rear ones because I believe that it can be done with the engine in place, unlike the primary ones. Please correct me if I am wrong
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Majorn View Drop Down
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  Quote Majorn Quote  Post ReplyReply Direct Link To This Post Posted: 14-Mar-2010 at 20:48
I've heard that the engine has to be dropped to change the rear ones to, but please correct me if I'm wrong, would gladly be wrong...
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RobG View Drop Down
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  Quote RobG Quote  Post ReplyReply Direct Link To This Post Posted: 16-Mar-2010 at 16:25
umm, i one of my back ones replaced, the one with the longer lead. My tame mech was able to do it without dropping the engine, but it involved skinned knuckles and jumping up and down over the front end like a yoyo
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