[FIXED] 2001 Volkswagen Polo GTI - strange 02

Hi Guys!

Today, I played around with my new picoscope advanced kit on my own Volkswagen polo 6N2 GTI with the 1.6 16V Engine (AVY).

I found, that the front O2 is sticking rich and the fuel System is permanent in open-Loop.
the aftercat-O2 is active, but very lazy.

I have no CEL, no DTC, no drivability Problems, nothing. the fuel-trims are also in a normal range (LT: 6%, ST: 1%) but the Monitors are not passed too for the o2-sensors and catalytic-converter. I mean, I drive this thing every day and didn't realize that there's a problem, because no CEL.

how is this possible?

for testing, i pulled the O2 Signal down to confirm the wire-integrity -->OK. Also the heater is controlled by PWM.

I ordered a new O2 today, but I have a big questionmark about this polo now!


Any ideas?

BR Matthias

Do the short term trims ever switch back and forth? Or, are they just stuck at the values you observed?

I think I'd start with a glance over the other ECM inputs for anything obviously out of range or irrational. ECT, IAT, TPS and such. A skewed cold ECT, for example, might fool the ECM into thinking the engine isn't warm enough for closed loop.

I'd be interested to know if you leave the O2 signal shorted low, would the trims ever respond? It should set a code eventually, too. Either one would give me more confidence in the ECM's ability to observe inputs and react accordingly.

the STFT is bouncing very slow around and Responds of a snap-throttle.
I checked the STFT while i pull down the O2 --> -25% and the engine Begins to shake, so, this part is ok.
i can't find any abnormal input-values on the ECM too.

This car uses a broadband-sensor if i'm right (5 pin). i'm not familiar with those sensors. This type of sensor should oscillate like a normal O2, right?

Ahhhhh yeah, I kinda suspected there might be a wide band at work! Unfortunately I don't think they sell the GTI Polo in the US? Otherwise I'd find a wiring diagram. :silly:

The wideband won't oscillate like a normal O2. In fact, your signal and trim behavior is very normal for a wideband sensor. It's also a good sign that the short term trims react to throttle movement. That makes me think that the ECM actually IS in closed loop.

You can try creating a small vacuum leak and see how the trims respond. If they go positive, I'd argue that closed loop is actually working.

VW did use wideband sensors on some Polo GTI see this page for connector picture www.gendan.co.uk/product_LB2088.html

YES, exactly this connector i have as Andy.McFayden found.

I've monitored the Fuelsystem-status while i was driving -->it switches from OL to CL permanent, few minutes in CL, then again in OL. I've never seen this before on a normal working system!

The STFT jumps to +25% as soon i create a vacuum-leak (my brake-booster hose snapped and broke in this experiment, the hose was that much brittle...)

in fact, i bought the new O2 for spare, is this correct?

Thank you very much guys! i've learned much in this case! This helps me a lot for further cases!

BR from switzerland!
Matthias

This is the snap throttle test for a wideband what I call the dippsy doodle test --- actually a Toyota so details are different it is the general pattern and almost instant recovery that is important.

www.diycardoctor.com/air_fu6.gif

Andy.MacFadyen wrote: This is the snap throttle test for a wideband what I call the dippsy doodle test --- actually a Toyota so details are different it is the general pattern and almost instant recovery that is important.

www.diycardoctor.com/air_fu6.gif

:lol: I like the name! This is a fantastic test, applies to pretty much everything.

kostelectronics wrote: I've monitored the Fuelsystem-status while i was driving -->it switches from OL to CL permanent, few minutes in CL, then again in OL. I've never seen this before on a normal working system!

When did you notice it going to open loop, exactly? I ask because it's not unusual to see wideband systems aggressively switch to open loop during fuel cut deceleration, or any time you lift off the throttle on some vehicles.

The STFT jumps to +25% as soon i create a vacuum-leak (my brake-booster hose snapped and broke in this experiment, the hose was that much brittle...)

Yep, that's a good response to a large leak. Sorry about your hose, though.

FYI, the scan data you saw showing the upstream O2 as stuck rich is misleading, and probably a product of early OBD standards that hadn't quite caught up with wideband sensors. Newer makes/models do a much better job of presenting wideband sensor data in a useable way.

Thank you again for those nice explanations!

I've found no regularities about OL/CL status. Once is it in CL at the traffic-light and once is it in OL at another traffic-light. But i think under load (acceleration) is it ever oin CL.

all in all it's very strange for me, but i've learned a lot (and bought a new O2 for nothing, but this is learning-money)

I think this case can now closed!

BR Matthias

Strange loop behavior. I guess we can chalk this up to an early wideband application?

For more reading, we've got a wideband thread going in the Diagnostic Tools section. As far as wiring testing, yours will most likely behave like a Nissan six wire design.

www.scannerdanner.com/forum/diagnostic-t...-testing-thread.html

As far as the monitors not being completed, may I suggest clearing the codes and rechecking after driving for awhile? I've known vehicles to get 'stuck' in their emissions monitor checks for one reason or another. Resetting the codes and monitors allowed the computer to start over and complete everything.

All Monitors are passed now! This was my fault! When i was playing with the new Pico, i've cleared the DTC's (because i produced one by myself) and drove after for about 30 minutes. Then, These 2 Monitors that i mentioned above were not passed.
But after re-check few days later, all Monitors are pass! So, there was never a fault in the System! ....but i'm much more clever now about These oldscool OBD Systems!

BR Matthias