1.6 16V AZD engine 17604 / P1196 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1

[crok]

Dear Community, dear Crasher,


I need your help again.


I almost figured out everything on my car and I am close not to have any error or issue in any of the controllers in my car.. but..

But I still have one (hopefully last..) issue with the car.


The car: Seat Toldeo 1.6 16V AZD engine code (same as Golf MK4 and Bora)
I have a "sporadical" upstream lambda sensor heater malfunction fault code:

17604 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1
P1196 - 35-00 - Electrical Malfunction

Sporadical means sometimes if I delete the code it won't come back in 100+km of driving,
sometimes after code clearing it pops up almost immediately again..

There are no other codes, no drivability issues, nothing at all, setting the readiness bits are easy as 123 when the lambda heater test does not give a fault code..

VCDS meas. block 041 is telling me that the resistance of the sensor heater element (with warmed up engine) is around 83..90 Ohms and one guy here who has a BCB engine told me that he has the same reading (and as far as I know both AZD and BCB are sharing the same genuine part numbers in terms of lambda sensors)


So the million quid/dollar/Forint/EUR question is:

If I would drive my car to your garage (what is not really possible since we are at least 1000 miles away unfortunately..) to diagnose the issue what whould you do? What steps would you take to rule out things to get closer to the resolution?


Thank you!!

[Crasher]

Is the lambda sensor new?

[crok]

My (ambiguous) answer is yes and no:
- yes, when it has been installed it was new but does the same thing since installation and
- no, unfortunately it was 2+ years ago..

probably I'm an idiot because I did not drive it back to this garage but when this has happened I was much more less experienced in automotive engineering and troubleshooting : | and I did belive in what the mechanic has said (little history behind the scenes..): I had P0420 (cat. converter efficiency below threshold) and the mech. diagnosed that the B1 S1 O2 sensor was faulty because it showed rich condition all the time.. it was between 0.75..1.1V all the time but mostly showed 1.05V.. after these years I figured it out that my O2 sensor was good because it is a 5 wire, wide band sensor and VW shows O2 voltage as lambda in these cars.. so around 1V means (almost) perfect air:fuel ratio.. (the mech 99.999% thougt that what he sees is a stuck-in-rich 4 wire narrow band sensor..).

So, your first guess is a faulty heater element or wiring in the O2 sensor, right? Like it has sporadic connectivity issue or something?

[Crasher]

I have seen a lot of corroded and damaged wiring at the gearbox mounted plug.

[crok]

This was my first thing to check and I don't see anything suspicious.
Absolutely clean plugs, no sign of water or any damage, sprayed a lot of contact cleaner spray in the plugs (terminals), many times - no luck.

[Crasher]

I have seen the wires snap further up the harness under the battery tray where the wires flex during engine movement. Follow the blue/yellow wire back into the harness where there is a welded connection which divides the power from fuse 43 off to the two lambda sensors and tank vent valve

[crok]

Is this welding point is in the engine bay area or in the interior area, like below the steering wheel? Yesterday I remoed the battery and followed the bl/ge (blau/gelb; blue/yellow) wire back until the point where the cables are distributed towards the parts and sensors, near the battery tray, but did not find any suspicious thing, not even a small piece of dust, really, clean, no trace of bending or any kind of wire damage. So I am chasing the welding point, probably it has been cracked due to "dry up".

This is a similar engine bay (from Google) like mine:
(Everything under the cable duct is bandaged - so I should unwrap them to find this welding point?)

1.6 16V AZD.jpg

[Crasher]

The VAG wiring diagram is incredibly helpful about this so called "welded connection" and even gives it a name, "E7" and it describes it as "Positive (+) connection (87a) in Motronic wiring harness" and thats it, as helpful as a kick in the balls.... From looking at the wiring diagram you can see it feeds both Lambda sensors and the EVAP valve and I think this welded point is for all three.

[crok]

Crasher, thank you for the wiring diag., that (and some luck..) helped me to identify what "87" means.. most probably..

I removed the panel under the steering wheel and checked the back of the fuse #43 just to see where the cabling is going.. so I was close to the relays as well.. then a wild idea came to my mind and removed the relay #409 , the fuel pump relay, and was shocked a bit because I saw the number "87" on it! So, from fuse #43 cabling is going to the fuel pump relay then to the O2 heater and lots of stuff.. most likely.. so, I removed the relay, cleaned it's connections and fit it back to it's place and removed and cleaned the cable and connection labeled "87F" as well (it has 87 on it..) - after 10 days and 500km - still no engine light (touching wood).

In this thread I've found some good pictures for reference:
VWVortex.com - Is the ecu relay 109? Awp dtc help

Fingers crossed..

[Crasher]

http://www.bosch-classic.com/media/e...eichnungen.pdf