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Oil warning lamp again, with a twist


jornyb

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Yes, the old subject is not closed.

Spent hours on this great forum without any success.

Been running a Fabia 16v, 22000km on the gauge, with the warning since May so i sincerely doubt any errors on oil pump or actual oil pressure.

I have that same symptoms as everybody else. The warning started intermittent but is now warning every time when revving above 1500 as it should according to mechanics handbook, http://workshop-manuals.com/skoda/fabia-mk1.

I have tried the following without getting the f*** warning to end. The buzzer drives me crazy :'(

As far as I can tell is there only one oil pressure switch on this model?

Must be something with the electronics but I don't have the common error with the gauges and I gave it a look and nothing looks corroded or loose but it's kind of hard to visually check the gauges.

 

Can anyone give advice, please?

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What year is the car, and engine code?

 

I'll have a look at the relevant current flow diagram when I have that info.

 

What do you mean by "I don't have the common error with the gauges"?

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What year is the car, and engine code?

 

I'll have a look at the relevant current flow diagram when I have that info.

 

What do you mean by "I don't have the common error with the gauges"?

It's a 2001. Engine code is AUA, sorry, i forgot.

There is an error when the gauges go crazy, flashing lights and meters turning described in this forum in several posts but I don't have that error.

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I think it's most likely to be a solder joint crack where the green connector attaches to the cluster PCB.

In pub now for a bite to eat though, will find relevant pin number when I get back to a big screen.

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Pin 23 apparently.  I'll have a look at a spare cluster later, and mark up a photo identifying the pin to look at.

Figured it out:

 

Cluster%20pin%2023.jpg

 

 

If you do get in here to look at/re-flow solder joints, be sure to also look at the two on that big round 750Ω resistor in the foreground of the picture. I've just found that pin 23 connects to the right hand end of that, on its way to anything else, so a dry joint there would be disruptive too.

 

You are correct that there is only one pressure switch.

I don't think the code-reader you have used would give fault codes from the Instruments module (clocks/cluster), do you know anyone with VCDS Lite?

Edited by Wino
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I removed the PCB tonight, I have 11V with no warning and 13V when the oil warning light comes on so it's unlikely with soldering errors and I can't find any errors with the soldering, didn't redo them yet because I'm waiting for a VCDS Cable from Ebay. I'll get back when i know more. My PCB doesn’t look as yours, I don’t' have the resistors you are mentioning.

 

25subvd.jpg

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I'll follow the circuit a bit further if I get a chance tomorrow. Is that resistor on the other side of the board on yours, maybe? I think you'll probably find one somewhere with the same colour bands, and the same physical size, which pin 23 connects to.

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Some success today with reverse-engineering the circuit.

 

Ignition 12V comes through a diode up near the 8-way connector and makes its way down the length of the board to one end of that 750 Ohm round resistor. The other end goes to pin 23 of the green connector, and so on towards the pressure switch. That point also goes to another resistor in a tiny quad pack of 4 individual 56K resistors near a big microcontroller chip. After the 56k it goes straight to a pin of that chip, which I guess is a digital input simply sensing high or low.  On the back of the board, that pin also connects to a capacitor (I think) in a tiny pack of 4, probably for noise filtering.  Like this exquisitely penned sketch:

 

20160829_184102-1.jpg

 

 

Picture below shows the micro pin, an adjacent test point, and the 56K resistor.  I'm a bit surprised to find more than 5V going towards a micro pin, was sort-of expecting the 56K to be part of a potential divider taking it down lower, but I can't find a datasheet about that chip so I just have to accept that it's happy about that situation.

 

20160829_184024-1.jpg

 

 

 

This cluster is a 2005 build, so may differ in a few details, but I doubt it's hugely different in principle. So not much to the circuit, and I still think a connector pin with a dodgy solder joint, or that current-limiting 750 Ohm resistor with a cracked joint are prime suspects.

 

:)

Edited by Wino
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Thanks, I'm impressed.

Your sketch makes sense with my voltage readings, 11V with no warning and 13V with warning. I think it also implies that the soldering for the 750 Ohm resistor is correct, if they would be faulty the reading would be 0V and I also simply can’t find the resistor?

Soldering around the IC and the 56K resistor is simply impossible so I’ll try to get my hands on a second hand. I’ll get back.

 

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Just want to confirm this is not just the car reminding you that you are due a service and/or have not reset the service indicator ?

My son had a flashing oil lamp once at motorway speeds and that is all it was.

Also, I read once that VW/\Skoda use 2 levels of oil pressure warning - the usual one that goes out once you get any kind of oil pressure and a second level indicator that looks for a higher pressure when the engine is running at higher speed - say 2000 or whatever.

Edited by poiuytre111
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Where are you measuring that 11V and 13V, at the pressure switch connector? With it connected to the switch, or not?

I measured it at pin 23 behind the PCB with the car running, see post #5

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I would expect the voltage at pin 23 to be 0V when the oil pressure is OK with engine running  (i.e. pressure switch goes closed circuit, shorting the wire to ground/chassis), so this may suggest a wiring problem between pin 23 and the pressure switch? Or an earth connection problem?

Edited by Wino
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  • 1 month later...

Solved

I know that you recommended to check the cabling but I felt that it was just a hassle and before I got to it a got a problem with dark left front light, glowing left turn signal and the speedometer was dead. I opened the big cabling to the left of the engine in the bottom of the engine bay and it was just a mess. The error was between the curve where the cabling rotate vertical and the engine bracket.

I had to replace 5 cables that was rotten. I planned to add a picture but the forum won't let me :(

Thanks very much for all you effort, much appreciated.

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  • 1 month later...

Some pics sent through by the OP:

 

IMG_2979.jpg

 

IMG_2980.jpg

 

IMG_2981.jpg

 

Unfortunately it seems easy to imagine that more and more old Fabias and related models will suffer these sorts of issues, due to the way the water can and does find its way down these stretches of wiring from the 'water-box' area.  The seal between the front panel of said box (where the ECU attaches) and the body of the car is the same light foam as the infamous door carrier seals if my memory is working. 

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