[Biturbos4] Cheap O2 Sensors

Keman keman at interwolf.net
Sun Dec 14 19:12:32 EST 2003

I'm not sure if this topic has come up before .. if it hasn't, here is some
interesting info if your precat O2 sensors are popping the dreaded
"resistance too high B1/2 S1" codes.

You can spend $180 at the dealer .... or $22. Your choice. The latter is a
VW part .. and it requires a splice to your existing connector. Parts can be
seen at...


Now I have seen people report these worked fine for the secondary O2
sensors.. which I don't really understand. I've had them both out and they
are different bosch part #'s. I figured they were different calibration ...
Damned if I didn't throw the piece of paper away at work where I wrote them
all down. Argh.

I do know that in VAG I saw a much higher voltage coming from the post cat
sensors after I uh.. altered the cats, vs. the upstream sensors. 0.95
downstream vs. around 0.53 volts upstream. It's the same exhaust gasses it's
just moved a couple of feet.

Speculation-- The reason people may report these work well downstream is
that the ECM is very flexible with what the downstream sensors can report.
So if they report a lower voltage ... who cares? The heater resistance value
is the same so everything is ok. It just thinks the cats are working very
efficiently. So the folks running the wrong sensors may never notice any
problem. And an interesting side effect of this .. is that those sensors may
then become the really, really easy way to eliminate precats and/or run
aftermarket downpipes. No diode necessary if the new sensors are reporting a
lower voltage than they should be.

Looks like I get to be test guinea pig if noone here knows... because my
secondary O2 sensors which are now reporting the proper voltage sans cats
... have dead heater elements in them. Strangely, they both show 25.5k ohms
of resistance after they get all warmed up. A week ago it was just one of
them. I'm not positive but I suspect that's the extreme end of measurement
the ECM can make. This dead heater element problem cropped up about a month
ago, before I started playing with the exhaust btw ... it is not related to
the diodes or anything I've done.

The odd part is, I could have sworn I got a precat O2 sensor heater
resistance error too not long ago ... so I'm probably going to just say fsck
it and toss all new O2 sensors on it. At $22 a piece, any improvement in gas
mileage would pay for them in a year.

Also, I've not seen a VW part up close but if it has the normal flat pin
style leads in the connector just like ours... I probably won't even have to
cut the wires because the connectors can come apart. Most of our plugs and
pigtails just require a small tool inserted into the little slits and the
terminals can be extracted ... then they just snap with the wires into the
old plug. Presto.

If anyone has tried this, please let me know. If not ... I'll post the

- Keman

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