Disco 4 (LR4) Fuel guage issue

Good afternoon folks,

My 2009
D4 has just been to garage for MOT and a new passenger side blend heater motor.

Motor all sorted however randomly now the car is saying that it has Zero fuel in and zero miles on the range?

We’ve dropped more fuel in her and no difference, still reading zero, fuel light on and no codes /faults showing when plugged in?

Any help or advice greatly appreciated.

Hi probably the fuel gauge sender or it's wiring is fubar, https://www.disco3.co.uk/forum/discovery-4-fuel-tank-removal-wiring-sender-finished-178913.html

A known issue is the sender unit in the tank if the battery was disconnected while work was going on and the fuel was low it can cause the car to go into safe mode stopping it from starting if the fuel gauge reads empty.

Hopefully yours is still running if it goes into safe mode you need diag to get it reset before it will start again.

biketeacherdave said:

A known issue is the sender unit in the tank if the battery was disconnected while work was going on and the fuel was low it can cause the car to go into safe mode stopping it from starting if the fuel gauge reads empty.

Hopefully yours is still running if it goes into safe mode you need diag to get it reset before it will start again.

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The 'known issue' is L322 specific, given that the engine is still running means that the ECM is seeing some fuel in the tank, otherwise the 'driver inducement' misfire would be occurring, followed by an engine shutdown to protect the HPFP from running dry. Personally I'd try a battery disconnect / reconnect before anything else - make sure the vehicle has fully shut down (keys out, doors closed, bonnet open for 20 mins) before disconnecting the battery, then leave disconnected for 15 mins before reconnecting. The lack of DTC's suggest the wiring is intact and both sensors are providing some sort of output, if the battery disconnect / reconnect doesn't sort it, it's time to get the multimeter out...

The three wires for the level sensors are connected to the CJB and values broadcast on HS-CAN.

Reviving an old thread here but @Graculus and @biketeacherdave, I'm hoping I can benefit from your experience here.

I've been in an absolute fight with my brother's L320 (2010 TDV6) over the hand brake module etc. and having finally got all that working and all the rusty bits replaced, it "Died" at the alignment place.

Since we did all of this work and have had the battery on and off multiple times it's started showing 0 miles range and an empty tank which we knew wasn't the case but it is brimmed now and as it's not actually leaking and has covered about 4 miles, we're confident there is diesel in it. Even the best jokes about LR fuel economy can't stretch to that!

Slightly differently, his car did show a full tank of fuel when he braked but that stopped happening after a few minutes from leaving the petrol station and it steadfastly remains at empty now. The RRS is exhibiting the classic misfire about every 4-5 seconds and then shuts down after a minute which you could pretty much set your watch by and to me that is too manufactured to be a failing fuel pump, it's got to be it protecting itself and if fires up instantly when you press the button.

I've spoken to him this afternoon and he's going to follow the steps as you suggested in the post above, but I wondered if there was a reset/recalibration type of thing that could be performed with GapIID as I have that and a licence for his car. Did it sort your problem Dave just by doing another battery reset?

The diagnostic shows very little other than "Restricted Perfomance due to lack of fuel". There is nothing I can find for communication or fuel pump/sender being logged and it was working perfectly before we did the EPB.

Appreciate any tips here and I'll update with my findings.

The car is in fail safe it thinks its empty so won't let you start the engine. I'm not sure if the gap tool will reset the fuel sender unit but I don't see why not.
Think we used LR diag to reset my mates car.

It just needs the fuel level reset is all.

Good luck report back

It does start mate but it does all the things that Graculus suggests is specific to the L322.
I'll see if I can find the fuel level reset in Gap.
I'll let you know.

You should be able todo a full vehicle reset with the gap tool to sort the issue.

Yep, it's in 'driver inducement' mode - so it's registering zero fuel, not lost calibration. You say it briefly showed 'full' when you braked so either there's a loose connection / damaged harness from the EPB remove & refit exercise (the harness runs over the top of the chassis rail IIRC) - or it's possibly one of the senders in the tank has come loose and is floating on it's side in the diesel...

If you meter the wiring through from the inter-harness connector in the NST wheelarch to the tank connector, you should be able to prove/disprove harness damage as a cause.

The only thing specific to the L322 is the 'memory' of the fuel level, L319/320's don't suffer that problem and unless you'd drained some fuel off whilst the tank or battery was disconnected, it wouldn't be an issue anyway.

Known issue

So basically, I'm dropping the fuel tank then. Yeah, I really do NOT want to do that and most notably because it has at leat 75l of fuel in it and I'm saying that because I know it has a smaller tank than my L322 which is 100l but this bugger is still full and there's no getting away from that fact.

Ideally, the Main harness connector in the NSR arch would be a good place to start as we could conceivably use a meter to prove whether the sender is "there" or not and to prove part of the wiring. If it's open circuit, I'll know the issue is between the connector and the float.

I want to trick the car ideally, if it doesn't have the memory issue, can I ground the pin from the connector to make it think (or in this case know) it is full and then at least drive it a bit, bed in. the EBP etc. and perhaps run off the excess fuel from above the tank (pretty sure the neck is full too). I could do 100 miles or so comfortably and then drop the tank at the weekend meaning I'll only spill 20 -30 litres all over myself and the garage floor! We all know that mess is coming whatever happens!

Yep, you can do that - I'd suggest using a resistor at the NSR wheelarch connector to 'prove' the circuits (remember there are two tank senders) There is an anti-syphon valve in the tank filler spigot so you'll just have to catch the contents of the filler tube (and have two replacement jubilee clips because the ones fitted at the tank end are single use only (or should be).
It's not too bad a job to do on the ground, if you have two trolley jacks, if you have a lift, I'd suggest getting it on that forst and making sure all the fasteners will come out, one at a time, and take off the heatshield & EPB release cable whilst it's in the air.
Use a short piece of scaffold board fixed to the trolley jack (take the cup off the trolley jack and bolt through the hole to secure) for the rear of the tank as that holds the most fuel and is therefore the heavy end.

I'm looking for a bit more help here please. We've had another crack at it this weekend and we're still no closer to finding the fault but perhaps understand it a little better, so, here's the current situation.

Drained the tank down and removed it. Done a continuity check across the wires from the multi-pug by the handbrake module to the tank. All is good.
Removed the tank cover and checked the wiring inside, I think because it's a 2010 model it has two senders in there, they share a common earth (Pin 1 I think on the tank plug and then Pin 2 for the front sender and Pin 6 for the rear one (well it's in the middle of the tank but it's not as far forward as the other one.
Both senders show in the region of 150 Ohms at their lowest point and 1k ohms at a full tank if you move them with a Fluke meter on them so I'm going to say that they are both working as they both output the same resistance and I doubt both would fail together.

We then fitted 1k Ohm resistors to the wiring from the tank plug to the car and this is where it gets marginally more interesting. When you turn on the ignition, it shows a full tank of fuel on the gauge BUT the fuel light stays on and it tells you the fuel level is low. After about 30 seconds, the gauge drops to empty. Let the car go to sleep and the same thing happens again. Brother says that when he filled it before, it showed a full tank but he's fairly sure the light stayed on then too.

What I think is happening here is that we have wiring damage (not that we can find it (yet)) and that one level sensor is working and the other isn't so the car is applying "logic" to say that if one sender is bottomed out and the other is working, it could be the fuel moving around in the tank, after a while (say 30 seconds) this hasn't changed and therefore it is better to be pessimistic and take the view that there is no fuel rather than plenty. Therefore we accept that there is no fuel and put the light on, warn the driver etc. Does that seem feasible? Or am I wildly off the mark here?

It seems that if we could extinguish the fuel light it would work but I suspect that is only turned on by the BCM based on data received (or not) from the level senders. Basically, I'm bloody certain this is a wiring issue as we also now have Adaptive Roll Bar pressure valve open circuit error and parking brake module won't communicate and so on. All in that area but with the caveat that we can can't find anywhere that we have damaged the wiring and that it seems not to run where we've been working save for the tank wiring which we've proved today.

Next steps (as we forgot to do it today) will be to make sure that although we have continuity on the fuel tank wiring, we didn't buzz the pins to ensure there aren't any dead shorts across any of them. That's a five minute test though, once that's done, I feel the tank can go back in the car comfortably.

Any thoughts? Of does anybody know which way the wiring goes from the big multi plug on the NSR? Does it run along the chassis rail or into the body in the NSR quarter, I think it's the latter but I'll open the floor here. If I'm honest, I'm getting a bit fed up with this handbrake module replacement job now!

The wiring runs up into the body in the rear quarter, then on to the BCM - continuity checks to the BCM together with short to ground and short to positive checks - I doubt there's be any mutual shorts. to eliminate the BCM, put the resistors across the BCM, you're right in assuming that the low fuel light is triggered by low resistance on one of the sensors, even of the other is giving a correct signal. Did you measure voltage on the signal wires? they should both be the same open circuit and very close with resistors across the connector a low voltage under load would indicate either a bad BCM or wiring to it.
It's generally more useful to measure wiring voltage (with a real or dummy load applied) as volt drop is more easily seen than resistance in an un-powered or loaded circuit. or to put it another way, 'resistance is futile'.

Thought I'd better update this thread to explain what happened here.
After removing the tank and checking all of the connections, sender operation and wiring back to the the Body Control Module and being unable to find a fault, we considered replacing the BCM.
Whilst having GapIID plugged in and downloading the config (just in case) I found that there was an ECU update for the Instrument Cluster (IPK); in a bit of a frustrated gamble I re-flashed it and wouldn't you know it, the bloody thing only started working again! The car is no longer in driver inducement mode, starts up and runs as it did before whilst showing what we believe to be the correct fuel level.

Got a few other issues to work through but for now at least, that bit is resolved and we can present it for MOT (expired a couple of weeks ago as it was off the road). So pleased with this result and thanks to all for the support as always.

Blob said:

Thought I'd better update this thread to explain what happened here.
After removing the tank and checking all of the connections, sender operation and wiring back to the the Body Control Module and being unable to find a fault, we considered replacing the BCM.
Whilst having GapIID plugged in and downloading the config (just in case) I found that there was an ECU update for the Instrument Cluster (IPK); in a bit of a frustrated gamble I re-flashed it and wouldn't you know it, the bloody thing only started working again! The car is no longer in driver inducement mode, starts up and runs as it did before whilst showing what we believe to be the correct fuel level.

Got a few other issues to work through but for now at least, that bit is resolved and we can present it for MOT (expired a couple of weeks ago as it was off the road). So pleased with this result and thanks to all for the support as always.

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Really pleased for u mate and bet that was a huge sigh of relief when it started