Hello,

 

I have a Skoda Octavia 1U2 equipped with a 1.6 engine with code BFQ, from 2004 with troubles regarding lambda, oil consumption and incomplete self diagnosis.

 

TIMELINE/BACKGROUND

2023 late autumn
Troubles started this time when the engine light turned on for the first time.

 

2023 late autumn till end of year
A period followed when the engine light turned off and on intermittently without altering anything.

 

2023 end of year
We went to read the fault code at a local motor vehicle expert shop because the annual inspection was about to happen. The fault code referred to the upstream lambda (i cannot remember the fault code because at that time i did not own an OBD reader and i lost the notes i made back then).

 

2024 january
So this lambda sensor got replaced by a new one and the inspection was passed.

 

2024 february to march
But shortly after the engine light turned on again. And again a period followed when the engine light turned off and on intermittently without altering anything.

 

2024 march to october
This was a period when the engine light was off. We made several long distance trips between 1500km - 3500km. Oil consumption during this time was acceptable but increasing and oil was refilled regularly.

 

2024 september till today
The engine light turned on again and stayed on eversince. We did a few trips of 1500km. oil consumption was increased. I bought an OBD reader and the fault code was P0130 (O2 sensor circuit bank 1 sensor 1).

 

OBSERVATIONS

I went to ask a repairment expert about the costs but he said the problem can be anywhere so i might end up paying more than the car is worth. So i asked for some advice what to check for save money and here are some findings.

 

OBD I/M readiness

• MIL status ON
• Misfire monitor OK
• Fuel system mon OK
• Comp component OK
• Catalyst mon OK
• Htd catalyst N/A
• Evap system mon INC
• Sec air system INC
• A/C refrig mon N/A
• Oxygen sens mon OK
• Oxygen sens htr OK
• EGR OK

 

OBD live data

• DTC_CNT 1
• FUELSYS1 OL
• FUELSYS2 N/A
• LOAD_PCT(%) 26.2
• ECT(*C) 78
• SHRTFT1(%) 0.0
• LONGFT1(%) 9.4
• RPM(/min) 686
• VSS(km/h) 0
• SPARKADV(*) 9
• IAT(*c) 13
• MAF(g/s) 2.28
• TP(%) 2.0
• AIR_STAT OFF
• O2S B1S12--BS2---
• O2B1S2(V) 0.435
• OBD EOBD
• MIL_DIST(KM) 3351
• EQ_RATB1S1 0.993
• O2B1S1(V) 1.469

 

Regarding idle, the specs say BFQ idles between 640-900 rpm. There are very slight fluctuations in the idling though...

 

• Lambda heater wire resistance 6 ohms
• Lambda connector harness pins 2 and 6 80 ohms
• Fuse 43 intact
  • See image 1

 

• Spark plugs changed in march 2022 (30 000km since)

 

• Air filter fairly OK?
  • See image 2

 

• MAF was pretty oily (cleaned now)
  • See image 3 and 4

 

• Tank cap sensor
  • Sensor disconnected
    • Power wire to ground 12.6V
    • Signal wire to ground 0V
  • Sensor connected
    • Power wire to ground 11.8V
    • Signal wire to ground 11.8V
  • Does somebody know how this sensor is supposed to work and how to properly diagnose? I assume this is related to EVAP?
  • See image 5 and 6

 

• Hissing sound coming from somewhere at the intake manifold. I think related to the solenoid valve as the hissing is most prominent at the places related to this. Does somebody know how this supposed to work? I could only observe the hissing at idling bcs i was alone diagnosing.
  • See image 7

 

• Oil was spread at the connection pipe between oil filler and intake pipe (is this the crankshaft ventilation valve?).
  • I disconnected the intake pipe to clean this part but at this stage this smaller connector pipe broke into pieces. I suspect it was already leaking/broken before i touched it hence the oil all over that specific spot.
  • Inside the intake pipe there is some valve or membrane which was also very dirty. I cleaned it with break cleaner (not sure if it was a good idea). This part has also two electric wires attached. Is this a sensor or a valve? What is the function of this? How to test it? For now i put the cleaned intake pipe back and fixed the broken pipe part with piece of hose.
  • See image 8 and 9

 

• Exhaust manifold seem intact in my opinion but also there traces of oil was visible at the manifold.
  • See image 10, 11 and 12.

 

• Oil and filter have been changed during these days of diagnosing.

 

After each change i reset the fault code and did a drive cycle but the fault returns.

 

Assuming that the lambda sensor is fine, my best guess is that something is altering the crankshaft pressure regulators and results in oil being pushed into the air intake and through the gaskets and exhaust where it then contaminates the lambda sensor. Someone also told me it can be the valve insulations that cause the spread of oil basically leading to the same result.

 

But i am a noob and i would appreciate any advice in further diagnosis.

 

 

 

 

 

 

 

 

Edited 29 December, 20241 yr by Treb_Kavon

1.

I would start by addressing the hissing sound as a priority. Any air leak after the MAF can cause idle fluctuations and alarms, so make sure all is well in that area. 

A. Replace the broken connection between oil intake plastic adapter and air admission pipe or, at least, be pretty sure there are no leaks there in order to proceed.

B. Check the air admission pipe integrity, the one coming out of the MAF. Also make sure the breather valve (membrane) inside is in good condition. Depending on your mileage, I would also replace this pipe, especially after reading the MAF was oily, as the breather might not be working properly. 

C. Check/replace the thinner air connection pipe  going from the small exit  (shown in pic 8) in the air admission pipe to the rocker cover area.

D. Check for leaks in vacuum pipes. I replaced all of mine as a preventive measure.

 

2.

The solenoid valve you mention, next to the intake manifold, applies vacuum to flaps inside the intake manifold, making them turn in order to allow more or less air into the combustion chambers. 

 

3.

Concerning the electrical connector in the air intake pipe, check here:

 

4.

As for the oil consumption/leaks, have you checked the following? You probably have, just making sure. 

A. Air breather in air intake pipe working properly. 

B. Rocker cover gasket leaks. 

C. Oil intake plastic adapter (on top of rocker cover) leaks; check integrity as it can crack, and also top and bottom seals. 

D. Oil residue in coolant. 

E. Oil pan leaks. 

I took care of A. and C. and oil consumption in mine was reduced by a large amount. 

 

5.

Sometimes, problems lie where you least expect them to be.

 

I had an ongoing problem with my AVU motor, consisting of:

1. Fluctuating idle (sometimes up to 1100rpm, others it would fluctuate from 1100 to 1300 rpm for a while);

2. One lambda probe replaced;

3. Several on and off ASR malfunction indications.

I wasn't able to come to the correct diagnosis, as the garage didn't, because everybody was looking for the problem in the wrong place. 

 

The culprit turned out to be the alternator. That was only detected when the regulator/rectifier shorted, frying one more lambda probe and the oil level sensor. In my case, the fluctuating idle was caused by the ECU trying to compensate for erratic voltages. I even had to replace a 2 year old battery, which is also a good indication that something is not well in the electrical department. Idle  is stable now, at around 690 rpm. 

 

Thank you @sirlancelotksa. I will carefully read this and try working my way through.

I had little time to focus a bit on the hissing sound. It definately is most prominent at the valve on top of the intake manifold https://www.lllparts.co.uk/product/06A198205A/repair-kit-for-valve-br-unit. This is in connection with the solenoid i assume. Can you elaborate more on this topic in terms of operation. I measured the voltage that goes into the solenoid with ignition on and engine off, it was 4.3V. The resistance between the pins of the solenoid was about 30 ohms. I read some people test it by connecting directly to 12V but since i measured 4.3V as input i did not dare to unleash it to 12V. There should be a ticking sound coming from it when the valve opens and closes. At what stage does this solenoid get activated?

Regarding the air intake pipe, for now it is fixed with a piece of hose. As tight as possible and sealed. The membrane in the pipe is possibly gone bad, not sure how to check its integrity but i was planning to buy a new air intake pipe. If the device attached to the connector pipe is indeed just a heater then i might go with the cheaper type without heater untill the issue is resolved. Tough i live up north so this might need to wait till better times...

 

Alternator seems to be fine, battery voltage at 14.2V steady when idling

I don't think the solenoid valve should be a concern at this point, at least from what you described; a bad solenoid would entail poor response when driving.

 

You mentioned 3 problems.
1. Oil consumption.
2. Engine light.
3. Lambda sensor.

 

IMHO:
1. Number 1. is hardly related to numbers 2. and 3.

2. However, oily pipes do tend to degrade, as you have noticed, and may allow unwanted air into the air admission circuit.

3. Despite the replacement of the shattered adapter, the breather in the air admission pipe might not be working properly, thus the oily MAF; in that respect, have you cleaned the MAF's filament as well?

4. You mentioned a hissing sound; I'd want to be sure of the vacuum pipes integrity, as they are 20 years old and fairly easy to check and/or replace. You can test them with a cheap vacuum pump, and see if they hold pressure, or just go ahead and replace them. Bad vacuum pipes are known to cause ASR and engine light alarms.

5. After getting that out of the way, you will be fairly sure that you won't be mislead in any diagnosis you attempt.

6. Numbers 2. and 3. might be related. The engine light probably came up due to the lambda sensor problem. You appear to have another problem with the lambda sensor, thus the engine light again.

7. However it might not be as straight as it seems. Check this thread:

 

8. Lambda sensors testing procedures:

lambda.pdf

 

9. Which OBD reader have you used? A generic one might not suffice in obtaining all the information available.

 

10. As per your request, here's info on how the flaps operate. Even though I found it in a paper related to an earlier motor, the principle of operation is the same.

01-flaps.pdf

 

11. The solenoid appears to be in good condition, as it is expected to have between 25 and 35 Ohm, as stated in here (these are procedures for AEH/AKL motor; in AVU motor the valve is slightly different, but the coil's resistance should be the same):

02-N156.pdf

 

12. If you want to test the solenoid valve and the flaps, test procedures as below.

03-solenoid.pdf

 

https://workshop-manuals.com/skoda/octavia-mk1/power_unit/16/74;_75_kw_mpi_engine/mixture_preparation_system_electronic_inj.gas/testing_components/test_intake_manifold_changeover/

 

https://workshop-manuals.com/skoda/octavia-mk1/drive_unit/1.6_l/75_kw_engine_fuel_injection_and_ignition_system/mixture_preparation_system_electronic_inj.gas/inspecting_functions/testing_the_intake_manifold_changeover/test_sequence/

 

13. I've never found information concerning the valve on top of the intake manifold, number 25 in the diagram you sent the link to, the one you say the hissing sound might be coming from. I do believe it to be part of the vacuum circuit that operates the flaps, working as a pressure limiter; that's why you can listen to air flowing through the valve as a hissing sound. Unscrew it  (requires a bit of force in the initial stage) and check if the membrane is in good condition; if so, it should be ok.

Thanks @sirlancelotksa

 

You have provided a lot of useful information that helped me in the diagnosis. Now that the oil has been changed along with the oil filter and the air intake pipe and other checks are performed such as vacuum leaks and coolant quality, it got time to address the lambda sensor itself. Seems like it was the lambda sensor that got faulty. It isnt clear whether there really was a wiring problem with it or was it contaminated by the oil that leaked into the exhaust manifold. The sensor was quite sooty. It looked like the one labeled as "POLLUTION FROM A RICH FUEL MIXTURE / POLLUTION FROM ENGINE OIL" from this website https://triscan.com/en/news/lambda-sensor-error-codes-are-often-misleading

 

Anyway the problem is now resolved so thanks for your help!

Glad all is well now!

 

I find the Octavia Mk1 to be a very nice car and worth investing time in; that's probably why I have two and am very reluctant to let them go.

 

Good luck with it.