Hi Guys

If you disconnect the vehicles 12v battery for period (up to a day) is there any thing that will need resetting?

I'm assuming there is no radio code to worry about these days! 17 plate car.

Should be just reset the clock time. I've been told if you have gps (factory satnav) then it picks up the time from that.

You'll have a fault light on first start, but a quick drive round the block with some full lock to lock turns will clear that.

No radio code issue, that's paired with the dash ecu and automatically authenticates.

All you'll lose is your trip milage.

Thanks for the info.

I'm getting some odd electrical gremlins and my son suggested disconnecting the battery as it sorted some problems out on his car (not a Yeti). It's worth a try.

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What is the car that is being asked about?

@tankman have you done an all module scan of your car, does that show any fault codes, even intermittent ones ?

What electrical gremlins are you experiencing ?

2 hours ago, Ootohere said:

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What is the car that is being asked about?

17 plate Yeti 2.0 TDI 150 4x4 as in the first post.

Worth putting on a trickle charger / CTek if you have one of haven't already tried ?

@Urrell  I misread the post.  'Sons car'. 

 

The OP does not say what the car is other than a 2017.

You do not see the members signature to the left when reading on a phone, so no 'Yeti 2.0 TDI 150 4x4'. 

13 hours ago, Urrell said:

17 plate Yeti 2.0 TDI 150 4x4 as in the first post.

Yes it's definitely a Yeti TDI 150.

14 hours ago, aubrey said:

@tankman have you done an all module scan of your car, does that show any fault codes, even intermittent ones ?

What electrical gremlins are you experiencing ?

I haven't had a scan done.

One of the gremlins (if you can call it that) Is the fuel gauge reading max when the ignition is turned on. It reads zero when the ignition is off. The range shown on the MFD shows about 570 miles even though I have driven quite a few miles since last filling up. I assume the range gets its signal from the fuel gauge? The float is possibly stuck so when the rain stops I'll see if a light tap might free it if that's the problem.

The radio/sat nav has not been working as it should. You can't change radio stations and the sat nav is stuck on one map area. I'm not sure whether this is the common touch screen problem I've read about or not.

The car is a little slow at starting from cold so maybe it does need to go on a charger.

As yours is a 4x4 remember that the fuel tank is saddle shaped, over the rear prop shaft, so readings can sometimes take a while to stabalise and equalise between the two sides of the tank.

2 hours ago, tankman said:

the fuel gauge reading max when the ignition is turned on. It reads zero when the ignition is off. The range shown on the MFD shows about 570 miles even though I have driven quite a few miles since last filling up

 

Normal behaviour, the gauge always reads zero when the ignition is turned off, "quite a few miles" is meaningless in this context, you need to say how many, due to the geometry of the swinging float arm its hard for a fuel gauge to be accurate at 90-100% full tank, usually they are very slow to drop, the trip history and fuel consumption since fill up are used to give a more accurate full scale reading and for the calculation of miles remaining, this data was lost when your battery was disconnected.

 

Drive some more miles and both the fuel gauge reading and miles remaining display will become more plausible.

 

1 hour ago, Llanigraham said:

As yours is a 4x4 remember that the fuel tank is saddle shaped, over the rear prop shaft, so readings can sometimes take a while to stabalise and equalise between the two sides of the tank.

 

The saddle tank uses 2 sender units and there is no equalisation balance pipe between the two sides, it must therefore have 2 pick up pipes and some valve arrangement to stop it drawing air when the first side has run dry, I wish I had thought of that and studied the pick up/sender unit when I had mine apart in further detail.

 

In VCDS measuring blocks you can read the overall fuel level, example 40 litres, and the level of sender 1 and sender 2, example 23 litres and 17 litres.

 

I'm happy to be proved wrong about the absence of a balance pipe, I did not go specifically looking for it although it should be apparent, not having one brings complications as described above so better to have one if physically possible.

Edited 27 January, 20251 yr by J.R.

18 minutes ago, J.R. said:

The saddle tank uses 2 sender units and there is no equalisation balance pipe between the two sides, it must therefore have 2 pick up pipes and some valve arrangement to stop it drawing air when the first side has run dry, I wish I had thought of that and studied the pick up/sender unit when I had mine apart in further detail.

 

I'm happy to be proved wrong about the absence of a balance pipe, I did not go specifically looking for it although it should be apparent, not having one brings complications as described above so better to have one if physically possible.

 

Think you are right  and I don't think there is a balance or equalisation pipe between the two halfs, other than the bit of tank that goes over the top. 

I did over 50 miles last week with the gauge not dropping at all. I know it would have shown some movement by now.

Are we saying the fuel tank is positioned under the back seats? I had a look this morning and couldn't see any obvious signs. Maybe the carpet would need lifting to get to the tank sender.

32 minutes ago, tankman said:

I did over 50 miles last week with the gauge not dropping at all. I know it would have shown some movement by now.

Are we saying the fuel tank is positioned under the back seats? I had a look this morning and couldn't see any obvious signs. Maybe the carpet would need lifting to get to the tank sender.

That sounds exactly what both my 4x4's were like.
And yes the tank is under the back seats. Once the carpet is removed you can see where the gauge mechanism is fitted. From memory it is only on one side of the saddle.

Be patient, it will sort itself out, refill the tank if you are in doubt.

1 hour ago, Llanigraham said:

Maybe the carpet would need lifting to get to the tank sender.

 

I would have thought that obvious, there are access plates to be removed on each side for the dual level sensors, the one on the right is also the pick up pipe, filter  and roll over cut off valve.

3 minutes ago, J.R. said:

 

I would have thought that obvious, there are access plates to be removed on each side for the dual level sensors, the one on the right is also the pick up pipe, filter  and roll over cut off valve.

Stupid forum is showing in your post that as a quote from me when it was actually tankman that said it!
Crazy isn't it?

I've had an experiment and it was me highlighting the text to quote what you had quoted.

 

Instead of doing this:

1 hour ago, Llanigraham said:

Maybe the carpet would need lifting to get to the tank sender.

 

I should have done this:

1 hour ago, tankman said:

Maybe the carpet would need lifting to get to the tank sender.

 

every day is a learning experience.

7 hours ago, J.R. said:

The saddle tank uses 2 sender units and there is no equalisation balance pipe between the two sides, it must therefore have 2 pick up pipes and some valve arrangement to stop it drawing air when the first side has run dry, I wish I had thought of that and studied the pick up/sender unit when I had mine apart in further detail.

 

 

Our S max has a saddle tank over the prop shaft too. When I looked from underneath I couldn't work out for the life of me how it worked because a pipe to equalise the level would have to be on the bottom of each tank and I couldn't see anything of the sort so I have no clue how each tank is configured. I assume it only had one lift pump so not sure what sort of wizardry is going on but as there are literally a hand full of 4x4 S-max's out there, there is limited information.

The internal pipe will be a pick up pipe for the second half of the tank, the lift pump will draw from both reservoirs together but there must be some valving to isolate the first side to empty or the pump would suck air when there was fuel remaining in the other side.

 

When mine ran out (I pushed my luck too far) and I was using VCDS to prime the system I looked at the fuel level measurements, both sides showing zero litres, after using a jerrycan it had 5l in the right hand reservoir and still nothing on the left.

I'm a bit embarrassed to say that I might have been worrying too much about the fuel gauge reading!

Just filled up today and it only took 10 litres of diesel.  I thought it might have taken more.

Thanks for all your input on the matter.

 

1 hour ago, tankman said:

I might have been worrying too much about the fuel gauge reading!

When we have filled up, it seems to take ages for the fuel gauge to show its taken any out.

Sometimes it takes 90+ miles to show any movement.

6 hours ago, J.R. said:

The internal pipe will be a pick up pipe for the second half of the tank, the lift pump will draw from both reservoirs together but there must be some valving to isolate the first side to empty or the pump would suck air when there was fuel remaining in the other side.

 

When mine ran out (I pushed my luck too far) and I was using VCDS to prime the system I looked at the fuel level measurements, both sides showing zero litres, after using a jerrycan it had 5l in the right hand reservoir and still nothing on the left.

 

The pump is a submersible in one half of the tank so it can't pick and choose which tank to pull from. It has to get from the non pumped side to the other either by a seperate pump or maybe some kind of venturi system. Like you have said, it can't do it in a way in which air can be drawn in.

Of course it can, it will have a feed pipe going from the LHS to the pump on the RHS with a valve that closes when there is no suction resistance, the opposite to the safety valve on a butane/propane cylinder regulator.

 

There is no seperate pump, please enlighten me on this venturi system that you speak of.

46 minutes ago, J.R. said:

Of course it can, it will have a feed pipe going from the LHS to the pump on the RHS with a valve that closes when there is no suction resistance, the opposite to the safety valve on a butane/propane cylinder regulator.

 

There is no seperate pump, please enlighten me on this venturi system that you speak of.

I'm not saying you are wrong btw, just thinking out loud. I only question your theory due to all the lift pumps I've seen just have a gauze on the bottom sucking fuel from its surrounding bowl but this of course could be totally different in this case.

 

Pass a fluid through a venturi (a restriction in flow sometimes via a small nozzle) before the restriction you get a reduction in velocity causing a higher pressure, in the narrow part of the venturi the velocity increases which creates a lower pressure area and depending on design*, a negative pressure. Same principle that a snow foam lance sucks up the snow foam from the bottle, or a pressure washer sucks up detergent from its bottle. In this particular scenario you would use the return flow to simply pull in fuel from the other side of the tank.

 

*I say design because a venturi or an orifice plate is often use in industry to easily measure the flow rate in high temperature/high pressure steam and water systems combined with a differential pressure transmitter. Flow being a square root of diff pressure.

 

I realise we have gone off on a bit of a tangent now, I just enjoy a good technical discussion🤐