Background:

Recently, the "12V socket" fuse (fuse 40 in the fuse box at the driver's knee) blew in my 2020 Octavia (MkIII) combi Scout (2.0TDI DSG-7). I'm not sure exactly when that happened. I'd had a 12V car cooler plugged in to the auxiliary 12V socket in the cargo area, and maybe also a typical USB car cigarette lighter charger plugged in in the centre console. The car cooler's plug has a 6A fuse in it, so the max it could draw should be 72W; not sure about the USB charger, but I think the two USB sockets on it are labeled 1A and 2.1A (and at most only one of the two ports was in use), so it's draw shouldn't exceed 11W. Total 83W. Even plus margin or minor surges, way beneath the 20A fuse that had been in fuse slot 40.

 

Whatever, stuff happens. I didn't have any spare fuses at the time, so I pulled the 15A fuse from the tow hitch (fuse slot 44) which we weren't going to be using on that trip, plugged it into fuse slot 40, and it blew instantly. (The centre console port was NOT occupied at that time; the car cooler's plug WAS still plugged in in the back though the cooler itself wasn't attached). I drove back from France to Spain with both fuses out.

 

I took the car to a local dealer here in Barcelona to ask them to look into the electrical system; they say they tested, didn't find anything wrong, and just put in a new 20A fuse.

 

I later went looking to see if maybe the 12V socket in the cargo area could short when something is plugged into it, (literally, in the act of pushing the plug into the socket), because I've noticed that the "wall" of the cargo area into which this socket is embedded is rather flexible. I pulled the fuse, set my multimeter on impedance, held the probes on the tip and the ring of the socket, and flexed the wall - nothing.

I put the fuse back in, plugged in the USB adapter and also the plug from the car cooler, all good.

 

And then I noticed, the shop had not replaced the fuse from fuse slot 44. And I also noticed that both fuse slots 13 and 41 (belt tensioner - driver's side, and belt tensioner - front passenger side) are empty.

 

I searched for "belt tensioner" and "octavia", "vw", "vag", and came up with a bunch of engine component stuff, and some references to a seatbelt pre-tensioner as part of the airbag system, but nothing to help me understand whether my car actually ever used those fuses. (A manual pull test on the two front seatbelts finds that, purely mechanically, they'll grab if pulled abruptly). 

I have the technical maintenance/repair manuals for the car; I only find the brief descriptions of how to repair components - nothing about whether those fuses are in-use.

 

Anyone know? Does a 2020 (last of the MkIII) Octavia combi use fuses 13 and 41, "belt tensioner"s ?

If so, what amperage should they be? (I found numbers ranging from 10A to 40A depending on car models, but none of those pages were specific to the Octavia MkIII).

 

thanks,

 

2 hours ago, JayLibove said:

A manual pull test on the two front seatbelts finds that, purely mechanically, they'll grab if pulled abruptly

This description is of a purely mechanical function of an inertial real seat belt.

 

Your fuses relate to seat belt pre-tensioners, which I sincerely hope you'll never need, but you'll be very grateful for should you ever be involved in a crash with a relative closing speed above 10 mph.

No your car does not have them. As you can see in the picture of your fuse box, only 1 terminal of each fuse slot 13 and 41 is occupied, this is the bus bar, the lower terminal has nothing meaning your car does not have them.

 

 

 

Edit: If anyone else comes across this thread and would like to understand it all a bit more, the seat belt itself has 5 safety systems (all at a very basic overview below)

 

The first is a torsion bar - Simply a metal bar made to deform if extreme loads are placed on the belt so the belt will have a measured amount of give to prevent too much cutting in to you when in an accident

Second we have a roll over lock - A metal ball bearing will lock the seat belt from releasing further if the vehicle is at a major angle

Third is the inertia lock which if the belt is pulled very hard or fast the mechanical prongs will lock the belt from extending any further

 

Forth is when we get in to the 2 electrical systems - First is the single use seat belt tensioner - this is a electronically controlled system by the airbag module which will fire a small explosive which will tighten the seat belt up completely and take up any slack at the time of an accident occuring.

 

The final electrical system as mentioned in this article is not a common one of the vw platform as normally an optional extra but often called PreSafe Assist - This is a non destructive and reusable system which will sense a possible incoming accident and react in 2 ways - First will wind all 4 windows up EXTREMELY quickly and close the sun roof. The second part that relates to this system are exactly the same as above in terms of a seat belt tensioner to take up all slack and put you in the optimal place for a face full of airbag. But it does this using a very very quick and torquey motor which will very quickly spool the seat belt of any occupied seat till its tight and holding the user firmly in their seat. 

Edited 14 August, 20223 yr by ApertureS

Fabulous explanation, thank you so much!

And, don't I feel a bit silly now (or, old, with less good vision than I once had...) - you're right, the missing second contact is quite obvious in retrospect 😅.

again, thanks!

  

2 hours ago, ApertureS said:

No your car does not have them. As you can see in the picture of your fuse box, only 1 terminal of each fuse slot 13 and 41 is occupied, this is the bus bar, the lower terminal has nothing meaning your car does not have them.

 

 

 

Edit: If anyone else comes across this thread and would like to understand it all a bit more, the seat belt itself has 5 safety systems (all at a very basic overview below)

 

The first is a torsion bar - Simply a metal bar made to deform if extreme loads are placed on the belt so the belt will have a measured amount of give to prevent too much cutting in to you when in an accident

Second we have a roll over lock - A metal ball bearing will lock the seat belt from releasing further if the vehicle is at a major angle

Third is the inertia lock which if the belt is pulled very hard or fast the mechanical prongs will lock the belt from extending any further

 

Forth is when we get in to the 2 electrical systems - First is the single use seat belt tensioner - this is a electronically controlled system by the airbag module which will fire a small explosive which will tighten the seat belt up completely and take up any slack at the time of an accident occuring.

 

The final electrical system as mentioned in this article is not a common one of the vw platform as normally an optional extra but often called PreSafe Assist - This is a non destructive and reusable system which will sense a possible incoming accident and react in 2 ways - First will wind all 4 windows up EXTREMELY quickly and close the sun roof. The second part that relates to this system are exactly the same as above in terms of a seat belt tensioner to take up all slack and put you in the optimal place for a face full of airbag. But it does this using a very very quick and torquey motor which will very quickly spool the seat belt of any occupied seat till its tight and holding the user firmly in their seat. 

 

2 hours ago, ApertureS said:

The final electrical system as mentioned in this article is not a common one of the vw platform as normally an optional extra but often called PreSafe Assist - This is a non destructive and reusable system which will sense a possible incoming accident and react in 2 ways - First will wind all 4 windows up EXTREMELY quickly and close the sun roof. The second part that relates to this system are exactly the same as above in terms of a seat belt tensioner to take up all slack and put you in the optimal place for a face full of airbag. But it does this using a very very quick and torquey motor which will very quickly spool the seat belt of any occupied seat till its tight and holding the user firmly in their seat. 

 

My Treg has this and it scared the sh**e out of me the first time it went off, I was in a retail parking area and nosing my way up to a junction, when a car went past at great speed and it triggered this pre-crash warning, the speedo lit up with a massive red exclamation mark and the seat belt tried to garrot me ! yanking me back into the seat   

Aperture S has given the correct chapter and verse answer.

 

I was going to ask did you actually know if these fuses were in place before and had actually been removed?

 

Also to say that if that were the case then the airbag warning light would illuminate and remain so even after the power had been restored requiring the fault code to be reset using VCDS or similar.

 

The pyrotechnic pretensioners are an important integral safety feature and if disabled by removing the operating voltage would trigger the warning system

4 hours ago, ApertureS said:

This is a non destructive and reusable system which will sense a possible incoming accident and react in 2 ways - First will wind all 4 windows up EXTREMELY quickly and close the sun roof. The second part that relates to this system are exactly the same as above in terms of a seat belt tensioner to take up all slack and put you in the optimal place for a face full of airbag. But it does this using a very very quick and torquey motor which will very quickly spool the seat belt of any occupied seat till its tight and holding the user firmly in their seat. 

F***k that for a game of soldiers!!!!!

 

I'm sticking to old school vehicles.

Hi ApertureS, two more things come to my mind about all of this, if you don't mind.

One is just a note, I had read in the Rescue manual for the car about a feature where, when the car detects a collision, it will rapidly roll up the windows, fire strenghthening bars across the doors, tighten the seatbelts, etc. I think that's seat belt safety system #4 in your list? Or, is #4 only tension-the-seatbelts *as part of the Airbag* fuse?

Otherwise, even #4 ought to have a fuse (or two), shouldn't it? The only fuses in the manual for my car which are labeled anything remotely like that are these two unused "belt tensioner" fuses. 

Am I wrong about the "slam bolts through the doors to keep them from popping open in a crash" feature being on this (or much of any) Octavias 2020?

thanks again,

  

15 hours ago, ApertureS said:

No your car does not have them. As you can see in the picture of your fuse box, only 1 terminal of each fuse slot 13 and 41 is occupied, this is the bus bar, the lower terminal has nothing meaning your car does not have them.

 

Edit: If anyone else comes across this thread and would like to understand it all a bit more, the seat belt itself has 5 safety systems (all at a very basic overview below)

 

The first is a torsion bar - ...

Second we have a roll over lock - ...

Third is the inertia lock ...

 

Forth is when we get in to the 2 electrical systems - First is the single use seat belt tensioner - this is a electronically controlled system by the airbag module which will fire a small explosive which will tighten the seat belt up completely and take up any slack at the time of an accident occuring.

 

The final electrical system as mentioned in this article is not a common one of the vw platform as normally an optional extra but often called PreSafe Assist - This is a non destructive and reusable system which will sense a possible incoming accident and react in 2 ways - First will wind all 4 windows up EXTREMELY quickly and close the sun roof. The second part that relates to this system are exactly the same as above in terms of a seat belt tensioner to take up all slack and put you in the optimal place for a face full of airbag. But it does this using a very very quick and torquey motor which will very quickly spool the seat belt of any occupied seat till its tight and holding the user firmly in their seat. 

 

The ignition system is never fused on a vehicle or at least never used to be, it has/had a fusible link section of wiring in the loom to burn out before the battery can set the whole loom on fire, usually too late, this was done because the engine running is considered mission critical, the airbags and pretensioners etc equally so, I would not be surprised to find they are not fused.

 

In any case anythin that prevents their operation like fuse removal or even a short comms disconnection will trigger a latched MIL light and fault code.

Edited 15 August, 20223 yr by J.R.

3 hours ago, JayLibove said:

Hi ApertureS, two more things come to my mind about all of this, if you don't mind.

One is just a note, I had read in the Rescue manual for the car about a feature where, when the car detects a collision, it will rapidly roll up the windows, fire strenghthening bars across the doors, tighten the seatbelts, etc. I think that's seat belt safety system #4 in your list? Or, is #4 only tension-the-seatbelts *as part of the Airbag* fuse?

Otherwise, even #4 ought to have a fuse (or two), shouldn't it? The only fuses in the manual for my car which are labeled anything remotely like that are these two unused "belt tensioner" fuses. 

Am I wrong about the "slam bolts through the doors to keep them from popping open in a crash" feature being on this (or much of any) Octavias 2020?

thanks again,

  

 

So I think you’re getting a bit confused. Number 4 is a one time use airbag controlled system, all of the airbag system is controlled by the airbag module which is fused.

 

the secondary system which is number 5 has its own fuse as the motors draw a lot of power for the reversible seatbelt tensioners.

 

and your mention of door bars exploding to strengthen the doors, i have never heard of that and I’m happy to be proven wrong but that sounds like a terrible idea. A major part of life saving systems is still to allow egress of the vehicle after an accident, by pinning the doors shut you’d prevent that. Having them mechanically or electronically retract after accident is not reliable as metals can twist and keep the doors from opening.
same way although a seatbelt will lock you in place in an accident, even hanging upside down with your full weight on the belt, the buckle will still open with relative ease with all that pressure on it.  

21 minutes ago, ApertureS said:

 although a seatbelt will lock you in place in an accident, even hanging upside down with your full weight on the belt, the buckle will still open with relative ease with all that pressure on it.  

I can confirm that from experience of hanging upside down in a ditch in my first car, a Renault 6

The door bars thing comes from a Skoda document "Guidebook for Rescuers" subtitled "RESCUING AND SALVAGING ŠKODA BRAND VEHICLES AFTER AN ACCIDENT" (order number S00 5186 60 20).

Aha, I may have misunderstood: perhaps this document wasn't speaking of an active protection system, but rather the unavoidable eventuality of reinforcing bars (static, to strengthen the car against side impacts) being forced into the doors, making the doors impossible to open after an accident:

 

"In ŠKODA vehicles, the side impact protection consists of steel profiles. The profiles are arranged horizontally and diagonally behind the door outer panels and in the sills if necessary.
In the event of a serious accident, the high-strength pipes/profiles can punch through the door panel and hook into the B-pillar (or C-pillar). Then, the door can no longer be opened."

 

As to the good or bad of an active frame strengthening system, given that car crashes do end up in doors being unopenable naturally, I'd consider such an active system depending on the whole universe of pros and cons (weight, probabilities of different types of crashes, stronger and weaker spots on the frame, etc). But in any case it does seem that I had mis-read the document.

 

This same document describes I think five different variants of belt tensioners (one of which is described as "reversible" and must be the one that uses the two in-my-car-empty fuse slots).

 

It would be nice to know everything that is, and isn't, in my car. Certainly the information that the dealer provided is inaccurate (it's a generic description of mostly standard stuff plus a bunch of optional stuff not all of which my specific vehicle has).

I do have a "Vehicle-specific information" report generated from my car's VIN (I forget from what website I got this), containing about 200 rows of Pr-numbers, but searching through that for "belt" or "tension" just comes up with the fact that the car has seatbelts...

  

44 minutes ago, ApertureS said:

So I think you’re getting a bit confused. Number 4 is a one time use airbag controlled system, all of the airbag system is controlled by the airbag module which is fused.

 

the secondary system which is number 5 has its own fuse as the motors draw a lot of power for the reversible seatbelt tensioners.

 

and your mention of door bars exploding to strengthen the doors, i have never heard of that and I’m happy to be proven wrong but that sounds like a terrible idea. A major part of life saving systems is still to allow egress of the vehicle after an accident, by pinning the doors shut you’d prevent that. Having them mechanically or electronically retract after accident is not reliable as metals can twist and keep the doors from opening.
same way although a seatbelt will lock you in place in an accident, even hanging upside down with your full weight on the belt, the buckle will still open with relative ease with all that pressure on it.  

 

23 hours ago, nige8021 said:

 

My Treg has this and it scared the sh**e out of me the first time it went off, I was in a retail parking area and nosing my way up to a junction, when a car went past at great speed and it triggered this pre-crash warning, the speedo lit up with a massive red exclamation mark and the seat belt tried to garrot me ! yanking me back into the seat   

I get the massive red exclamation mark❗treatment every so often, eg. turning left at a junction (single lane, but flares left) when someone is waiting to tun right.

I'm thinking of disabling Front Assist, if all it does is distract me when I'm already braking.

A❗projected onto windscreen + full beam headlights would be more effective and safer.

 

But I make a habit of sitting right against the seat back, then adjusting the seat for comfort. Then I 'pre-tension' the seatbelt myself, before driving. I've driven a lot of other vehicles (with permission, of course).

One friend whom I drive for, has an Octavia with 3 memory buttons for seat position.

2 minutes ago, zeta said:

I 'pre-tension' the seatbelt myself, before driving.

So do I. I can assure you, from personal experience, that the pretensioners get the belts tighter than you ever will in the event of a crash.

5 minutes ago, KenONeill said:

So do I. I can assure you, from personal experience, that the pretensioners get the belts tighter than you ever will in the event of a crash.

Oh yes, I'm sure they do. But I'm sure you'll agree, the idea is for me to move around as little as possible.

Holding me tightly is fine 😏 -- picking me up and throwing me into the seat is To Be Avoided.