We have Mk1 Octavia 2004 and the fuel flap has stopped working.  The release motor bolt is not jammed and motor shows a resistance on the meter (not open or short circuit) but I get no power to the connector, have no power at the switch but the fuse (F38) is OK, boot light and central locking also working OK.  I either am looking at the wrong fuse (the obvious culprit) but with no diagram I can only go by the fuse list.

 

If anyone has any ideas or can point me at a wiring diagram, I would be very grateful

Does the flap release if you hot wire it?

29 minutes ago, MGH said:

If anyone has any ideas or can point me at a wiring diagram

I have the workshop manual for the mk1 electrical system - a 10MB pdf.  I can PM it to you if that would help?

I haven’t tried hot wiring because I can’t identify + and - as neither side appears to be connected to chassis and in any event there is no 12v at the switch. 
 

Please, if you have diagrams I would grateful.  I’m new here, do you need anything from me to PM them? 

I suggested hot wiring it to rule out that the fault is not simply an open circuit or stuck solenoid, I was not 100% convinced of your fault finding rationale, for instance you are assuming that the switch would have 12v and feed the solenoid but it could well be switching a transitor output within the body control module that activates the solenoid or the switching may well be done by the nearest canbus module to reduce the cables in the loom.

 

I realise that a wiring diagram would reveal that but in the absence of one I would be testing the solenoid by hot wiring it, it may well have a back EMF protection diode across it in which case your multimeter on resistance or diode check range if it has one will reveal the polarity to you, also if you post the colours of the 2 wires we can advise which would be the negative.

Link to Octavia mk1 workshop manual electrical section (pdf) on my Google Drive share.

Mike,  Thank you very much for your link.  Much appreciated and a very useful manual but unfortunately, no wiring diagrams 😞

 

JR,  Thank you for your advice.  I have stopped stubbornly thinking that its a 'hard wired' circuit and accept that there must be some sort of 'switching' going on between  the dashboard switch, which works (metered) and the release motor , which also works ('hot wired' to a 12V source) 

 

Having put away my trusty 12v lamp tester and picked up a meter I can confirm the following:

 

Battery voltage 12.5V

Fuse voltage (to vehicle chassis) 12.5V

 

Dashboard switch (Blue/Red and Brown) 0V across the connector or from either wire to chassis  (there may be a very small capacitive milli voltage, too fast for the digital VM to register properly, would need to put a scope on it or maybe an analogue meter).  However, the switch is doing something, see below.

 

Flap release motor connector with dash switch open (Yellow/Red and Blue/Red)  0V across the connector but 10.9 V on Y/R to chassis, Bl/R open circuit to chassis

Flap release motor connector with dash switch closed (Yellow/Red and Blue/Red) 10.9 V across the connector

 

I would have thought 10.9V would be enough to get a noise, at least, from the motor but nothing 😞 (It is a whirry motor and return spring not a solenoid)

 

Where does the Yellow/Red wire come from and why only 10.9V?  Some sort of hidden 'switching' circuit?  Any clues would be gratefully received, from anyone please.

 

 

 

Were you taking the measurements with the release motor connected?

 

The 10.9v might be a stray voltage, if you have fuses spare then try flashing it to ground or better still via a resistor, it could be a monitoring signal for the release motor like the bulb failure warning system, the blue red wire probably is switched to ground via whatever controller does the actual switching.

 

Dont worry about your "hard wired" logic, I had exactly the same with my MK1 Octavia mainly because it was so reliable I was never exposed to the intricacies of the Canbus system, I did not even know it had one till after 12 years of ownership, had I been up to date like I am now I would never have had to scrap the vehicle through door locking problems.

 

Getting a MK2 was a vertical learning curve for me!

If you get nowhere with tracing the fault to the switching module or replacement/garage diagnostic time is too expensive your hardwired logic could actually save you, hardwire it to a fused feed and never worry about it again!!!!

 

The switch contacts might not be rated for the current but its used so infrequently I doubt it will be a problem, I cant even recall how the switch operates now, I think you press it but the control module gives a momentary output.

 

My poverty spec Yeti does not have the remote release or a lock on the flap, it has an old school locking petrol cap, another bullet that I have dodged!!!

32 minutes ago, MGH said:

Flap release motor connector with dash switch open (Yellow/Red and Blue/Red)  0V across the connector but 10.9 V on Y/R to chassis, Bl/R open circuit to chassis

Flap release motor connector with dash switch closed (Yellow/Red and Blue/Red) 10.9 V across the connector

 

This proves that the module is switching the blue/red to battery earth, the problem sounds like the lack of current/voltage being applied which may be a wiring fault or one with the module, it could still be a fuse though if the 10.9v is a stray or induced voltage, you could try hotwiring 12v to the Y/R and then pressing the switch.

The flap release motor is supplied from a common source with the central locking(Red/Yellow). The other connection (Blue/Red) goes to the switch on the dash. The switch then completes the circuit to earth (brown wire on pin 2) when pressed. If there is not power at the motor there may be a poor joint where all the power is fed to the central locking.

Fed via the Comfort Control Module or possibly the drivers door controller?

 

I'm not sure if the MK1 had that level of sophistication, mine was so faultless to the end that I never got involved, the MK2 definitely had a Comfort Control Module.

 

Just a thought, if the power comes from the central locking and ergo via the drivers door controller could this be a manifestation of a semi fractured wire in the door loop?

 

That was what scrapped my MK1 but had I known about it instead of trying to measure can bus voltages and diagnose without VCDS I could have saved the vehicle, when my doors were not opening I do recall the fuel filler cap also playing up, in fact it might have been one of the first warnings.

I think both central locking control unit and the loom junction where this red/yellow wire splits off from are behind the dash near fuseholder, not in the door.

Red/yellow is fed directly by the fuse (38) so it might be interesting to measure voltage at both ends of that fuse in situ if it's one of the nice friendly ones with accessible metal contacts on the top surface?

Thank you all very much for your input.  I have been away for the past week and have not pursued the issue further.  However, before I went away I discovered 'erwin' elsewhere in this forum and £7 later I located the relevant wiring diagram for our model Octavia  (attached).  It does look as though the 'live' Yellow/Red wire from Dash connector to Flap motor connector is open circuit or HR.  I will delve further and post what I find (or the work around).

 

On 10/10/2023 at 15:56, Breezy_Pete said:

I think both central locking control unit and the loom junction where this red/yellow wire splits off from are behind the dash near fuseholder, not in the door.

Red/yellow is fed directly by the fuse (38) so it might be interesting to measure voltage at both ends of that fuse in situ if it's one of the nice friendly ones with accessible metal contacts on the top surface?

Full 12.5 volts on both sides of the fuse and central locking/boot light working ok.  Whatever he issue is must be after the fuse 😞  but thanks for the suggestion.  Diagrams support what you have said.

 

 

Connector A4 is a likely candidate.

Thank you again or all your assistance.

 

I'm going to upset the purists amongst you but this is an almost 20 year old car.

 

The problem was the live feed to the flap release motor  Red/Yellow.  I couldn't find connector A4 behind the dash but, as the Central locking and Boot lamp were all OK, I decided to cut the yellow/Red at the fuel flap motor (suitably insulated) and take a battery feed from the boot light.  All reassembled and working.

 

Thank you again for all your input and without Briskoda I wouldn't have found the wiring diagrams I wanted.  £7.50 well spent 🙂

3 minutes ago, MGH said:

I'm going to upset the purists amongst you but this is an almost 20 year old car.

There's now't wrong with pragmatism as long as the result works, is safe and appropriate.

A4 is an inline splice in the loom, where one wire becomes two or more, not a connector as such.

All you'd find if you did track it down would be a taped up lump with more wires coming out of one side than t'other.

All such 'connections' labelled with numbers inside circles on the circuit diagrams are this type of thing.

Well done for finding a workaround.