Erratic fuel gauge - Citroen Berlingo

[AP77]

Hi All,

I have a problem with an erratic fuel gauge on our Citroen Berlingo.

If I fill up with fuel (unleaded), generally the gauge will show full. Then after driving a few times the gauge will show an incorrect low level of fuel. It never shows empty, but will generally show much less fuel than is actually in the tank. Sometimes though, the gauge will climb back up to, say two thirds full.

My thinking is if it was an electrical fault, the gauge would either work or it wouldn't. Also, if it was related to a float in the tank, the gauge level wouldn't go up and down, it would just be going down.

Also, just to note, the fuel gauge does not move up and down according to gradient of the road, so it does not fluctuate visibly.

A bit puzzled to know where to start.

Any thoughts much appreciated.

 

[Burnerman]

Are there any other problems with the dashboard.....rev counter off, backlighting failed maybe?
John

 

[AP77]

Thanks for the reply. No other problems at all with the dashboard. Everything else working as it should. We have the problem for a long time now but would be nice to fix it. Garage suggested it could be the fuel sender but weren't sure and could be costly.

The gauge is always showing something, so am thinking if it is electrical it would either be on or off.

 

[Burnerman]

I’ve only removed the tank from a Berlingo diesel but didn’t need to remove the sender.
Anyway the sender is only accessible from the top when the tank is dropped and the fill pipe has to be removed too.
Unfortunately it’s a bit of a gamble but if the dashboard is otherwise behaving it is the solution I’d be going for.
John

 

[Avocet]

I've had some dealings with the fuel gauges on those. How old is it?

The way the fuel gauges work, (at least for the last 5 years and probably longer than that) is that they have a conventional sender with a float on an arm in the tank. It's all part of the same assembly that includes the fuel pump. When you turn the ignition on, it takes a reading from the float, BUT once the engine is running, it ignores the float reading! Instead, it calculates how much fuel you've used (by counting injector pulses). It then uses that calculated figure to tell the gauge what to say.

My guess, therefore, is that your sender is faulty and what you're getting, is a mismatch between how much fuel the sender is telling the car it has in it, and how much the onboard computer has calculated that it's supposed to have. Is the car standard in all other respects?

 

[Gasguru]

What happens if you're parked on a steep hill and the initial gauge reading is false?

 

[Avocet]

What happens if you're parked on a steep hill and the initial gauge reading is false?

The float is in the geometric centre of the tank, so it shouldn't change much with slope. It seems like a very complex system, to deliver minimal benefit really. It means you can have a tank that changes in cross section, and still have a gauge that is linear, because that's then just a fudge factor that you then apply in the software. It also means that the low fuel light comes on and stays on, rather than spending about 50 miles flickering as you brake or go round corners when the fuel level sloshes around and takes the float just above and below the level where the light would come on. I guess it means they can use the same basic pump and sender assembly in several different tanks and just alter the gauge response in the software too.

What tends to throw them, is if you just put a few litres in from a jerry can. It sometimes doesn't register on the gauge.

 

[Harry Bloomfield]

Not a Citroen, but my car has two senders, in two halves of the tank. Software integrates the values from both senders and adds an interpretation based on speed of fuel consumption, before it displays the fuel level. Start the engine from cold in my garage and the gauge might show almost zero and the fuel warning light be on along with 'FUEL LOW' on the display. It will then rise and the warnings go off, as consumption goes down with a warm engine. Putting just a small amount of fuel in the tank, takes some time to show on the dash, fill up and it immediately will show full. Maybe it is a similar effect you are seeing?

The way to check the gauge, is by replacing the sender with resistors, connected between the sender wire and earth. The workshop manual should give values of resistors for Full, 3/4, 1/2, 1/4 and empty. If those check out correctly, then it must be a faulty sender unit. Its just a float, on an arm, operating a rheostat (variable resistor).

 

[AP77]

Many thanks for the comprehensive replies, very interesting and much appreciated.

The van year is 2006. Parking on a hill does not affect the reading on the gauge, nor does going round sharp corners, driving down hill/up hill, etc. Also, once the level starts showing as low (almost empty), it doesn't then go back up again until I have refilled with petrol. Apart from this, one day it may show half full, the next day three quarters full.

The couple of garages I have asked seem unsure what the problem is, so I am fearful it will cost me just to find out it is not economical to repair.

It's a bit of a nuisance, but I think the simple answer is to keep resetting the trip button each time I fill up so I know to refill when I have done 250 mils or so.

Many thanks again.

 

[Avocet]

Many thanks for the comprehensive replies, very interesting and much appreciated.

The van year is 2006. Parking on a hill does not affect the reading on the gauge, nor does going round sharp corners, driving down hill/up hill, etc. Also, once the level starts showing as low (almost empty), it doesn't then go back up again until I have refilled with petrol. Apart from this, one day it may show half full, the next day three quarters full.

The couple of garages I have asked seem unsure what the problem is, so I am fearful it will cost me just to find out it is not economical to repair.

It's a bit of a nuisance, but I think the simple answer is to keep resetting the trip button each time I fill up so I know to refill when I have done 250 mils or so.

Many thanks again.

If you can live with it, that's certainly the cheapest option! If not, I'd be inclined to just get another fuel pump assembly from a scrapper and try it. There is an access panel in the floor, I think, under the rear seats. Take that off, and there should be an assembly with pipes on it, held into the top of the tank by a huge plastic locking ring. Peugeot have a special tool to undo / tighten it, but it can be done without that tool. Although it is good practice to change the big seal round the flange when you disturb it, my experience is that they nearly always re-seal! There's an arrow on the big locking ring, and a couple of marks moulded into the top of the tank. You have to do the locking ring up hand tight, plus however much extra it needs to bring the arrow to between the two marks.

I'm wondering if you have a "dead spot" on the potentiometer track so that below that dead spot, the computer gets a sensible reading from the sender and the gauge works as normal, but if you turn the ignition on when it's on its "dead patch", the computer doesn't get a sensible value and throws a wobbly?

 

[AP77]

Thank you for all the information. I may well try and get a fuel pump assembly from a scrapyard and try that.

Re. the access panel mentioned, you say it is behind the rear seats, I only have 2 front seats in the van. Would it be under the seats at the front or on the floor at the back of the van?

 

[Burnerman]

Pretty sure the van has a flat floor and no access panel....but if there is, I'm a complete dope when I dropped the tank on my 56 plate 1.9D
John

 

[Avocet]

Ah! You got me there! I'd forgotten it was a van. That might change things, I'm afraid. You might need to drop the tank. I've only ever worked on the MPV versions. I'll try and ask someone tomorrow.

 

[Burnerman]

If there is an access panel, please don't tell me.....
Had two major excursions under these, one was for rodent damage to the diesel return pipe and the other to fit a new rear axle that had developed major negative camber and boinging noises.
John

 

[cdbe]

I had a Citroen zx estate, dad to the Berlingo - access panel was somewhere in the back, I think under the seats - quick job to swap the sender unit.