o2 Sensor issues

[mb1907953]

One of the oldest ones in the (electronic vw) book... I'm having o2 sensor problems. I have done a search in this category for any previous threads but there isnt too much out there.

Long story short, I replaced my old o2 sensor (according to vagcom wasn't cycling between 0.2-0.9v within 1 second as it should be) with new ebay jobby in an attempt to improve fuel economy and what I believed to be slightly sluggish performance.

Ran about the same for a week or two but then went to ****. I have since had codes thrown left right a centre and couldn't get under 10L/100KM during a 400km road trip. Used to get about 8.4/ 100 on the old sensor (still isn't great).

The codes I have gotten are:

1) 00525 - o2 sensor intermittent signal
2) 00525 - o2 sensor short to ground
3) 00525 - o2 sensor implausible signal
4) 00525 - o2 sensor no signal

What is interesting is that when I plug in the Vagcom and check the lambda voltage on the new sensor, I am getting a fairly constant reading of about 0.345v (+- 0.005v). However, when I probe the actual harness connector in the engine bay, I get 0.66v absolutely constant. Why would it:

a) stay constant
b) read differently on Vagcom and the multimeter?

I must admit that I haven't checked wires but the old o2 sensor did still cycle, albeit it very slow. So am I just looking at a faulty ebay sensor? I thought this at first but others have had the exactly the same experience:

Bentley Publishers - Technical Discussions : Vr6 golf 00525 error code ...

If anyone has had any experience with this itd be greatly appreciated. Any continuity checks between the o2 plug and ECU would be a great help as well.

I have purchase a new legit o2 sensor here in oz but jsut dont want to put it in and find that the car is somehow frying them...

Cheers!
Max

[Jmac]

Pretty sure I sent you a long text with the answer to why the multi meter and laptop are different, they are not quick enough to read it real time mate. Scope the only real way. Ebay sensor a no go anyway, and slow, well they don't react slow so there is the answer mate. They must react quickly but on VCDS it wont be as quick as real time anyway.
Cheers
Jmac

[mb1907953]

Pretty sure I sent you a long text with the answer to why the multi meter and laptop are different, they are not quick enough to read it real time mate. Scope the only real way. Ebay sensor a no go anyway, and slow, well they don't react slow so there is the answer mate. They must react quickly but on VCDS it wont be as quick as real time anyway.
Cheers
Jmac

Cheers Jimmy, I do remember that text but I guesss i was confused as to why the multimeter wasn't changing at all? It just sat on a solid 0.66v which i thought was weird. But chances are I didn't have it contacting the signal properly or something. I've learnt a lesson there with the cheap ebay sensor. Will bite the bullet and pick up a decent sensor as my original one is completely buggered now.

Thanks mate.

[Umai Naa!!]

Jimmy is spot on. You really need to scope it to see what its actually doing.

One thing I've learnt over the years is that O2 sensors will log codes as a result of other faults such as unmetred air entering the intake beyond the air mass sensor.