C5 Fuel gauge stopped working after refueling

[paulcornwall]

I have a 2001 C5 HDI. When my wife was refueling I switched the ignition on then off and basically think i messed the computer up. Its now reading low fuel constantly despite just being refueled with £35 of diesel. I've tried searching but the search function fails. Can anyone help?

[Richard_C]

In the department of weirdness, my SAAB 9-5 wouldn't read fuel level properly if the petrol filler cap wasn't tight. No idea why, but a couple of times I just removed and refitted and all was well.

Worth a go (and free!)

[SaabC5]

In the department of weirdness, my SAAB 9-5 wouldn't read fuel level properly if the petrol filler cap wasn't tight. No idea why, but a couple of times I just removed and refitted and all was well.

Worth a go (and free!)

It will also show a "evap leak" message on the SID....quirks of Saabs.

[Suffolkpete]

When these computer thingies go doolally, a good ploy is to disconnect the battery for ten minutes

[C5Alan]

I've had this when I left the ignition on for the radio as there was a good song playing but I ended up getting paranoid that it really ws empty I ended up back at the petrol station filling up again and it worked fine after that

[Peter.N.]

I would concur with disconnecting the battery. When I bought my C5 I had one driven about half a mile along the motorway when it stopped, the fuel gauge was registering a little fuel and the light was not on but when the AA rescued me the tank was empty I subsequently disconnected the battery to trace an electrical fault, when I reconnected it the gauge went to zero and the light came on, its been OK ever since.

Peter

[paulcornwall]

I tried disconnecting the battery for an hour, reconnected and got Immobiliser fault, grrr. Managed to get rid of that my locking and unlocking the car, still stuck with the fuel gauge problem, I'm 90% sure its a computer bug type thing as this pnly happened when i turned the ignition on/off when the wife filled her up. Wheres the reboot button?

[paulcornwall]

bump

[Peter.N.]

I'm afraid your guess is as good as mine, a Lexia session might help.

Peter

[BX]

The solution is very simple. Just add at least another 15 litres to the tank with the ignition switched off and all will be well.
A few points about modern fuel gauges.
Most modern common rail diesel cars adopt the following strategy (with some slight variations) to ensure that the car never runs out of fuel and gets airlocked.
Accurate readings of the fuel gauge sender are only taken when the car is parked on level ground.
The body computer (called the BSI if its a citroen or Peugeot) will only take a reading if the level increases by a certain amount with the ignition turned off. When this happens it is assumed that the car is being filled on a forecourt which are mostly pretty level.
The gauge on the dash is then incremented to show this level.
As the car is driven the fuel is metered by the engine ECU. The amount of fuel used is communicated over the can bus to the body computer which decrements the gauge.
When the level reaches a predetermined low the out of fuel strategy is employed.
Most vehicles will stop but can be restarted if the engine is persistently turned over.
They will then run for a further 10 to 20Km before stopping again.
Some Fords employ a stutter technique to frighten the driver into filling up. They will stop later if not filled.
Once stopped 5Lis seldom enough to get them to restart instantly. If they stop 10 to 15 liters added to the tank will get the engine to fire up on the first turn.
As I say there are differences in the implementation of the strategy between the different makes but the general idea remains the same.

[Peter.N.]

Interesting. My C5 ran out of fuel with the light out and still an indication on the gauge but all operated correctly after I disconnected the battery, been OK ever since. Thanks for the explanation.

Peter

[reblack68]

A few points about modern fuel gauges.

Would that explain why the petrol gauge on my C5 goes down when I'm running on LPG? It seems to reset itself to the correct level if I park on a road with some camber.

[paulcornwall]

Solved - As suggested by a couple of you with special thanks to BX who took the time to pm me. Went to the petrol station turned the ignition off placed £20 of fuel in her and it strung back to life...yippeee. Can finally get to A to B with the fear of breaking down. So if anyone has this problem in the future try refueling with a modest amount to wake up the petrol gauge. Thank you all.