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Discussion summary
YOUR RESEARCHFuel gauge stopped working on my 996???
Reported or suspected cause
upper and lower segmentation
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Leading evidence: 'upper and lower segmentation' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'upper and lower segmentation' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check gauge' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
Once enough fuel is added to fill the lower section (ie up to the "flat") the sensor is "wet" and the gauge reads as normal (ie a measure of the entire tank).
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Suggestion
Note: in the diagrams below the "2WD" and "AWD" refer to chassis type, this means as GT models use AWD chassis and hence use AWD tanks.
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Suggestion
Once enough fuel is added to fill the lower section (ie up to the "flat") the sensor is "wet" and the gauge reads as normal (ie a measure of the entire tank).
Use awd's stronger chassis) have additional driveshafts
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Suggestion
The AWD models (so C4, Turbo etc and GT3 derivs, which use the AWD's stronger chassis) have additional driveshafts to and at the front (obviously), but this poses problems for the original position/size of the fuel tank.
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15 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
911uk: 1 discussions
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Outcome without a verified action link
Panicked as I thought it was something wrong, then when I fuelled with 97 RON fuel all the way it worked fine.
Hi there,
I topped up my fuel yesterday and the fuel gauge didn't move and yellow light stayed on?
Anyone else had this problem and is it easily fixable? I'm assuming it's just a faulty sensor.
Thanks.
Yep, 4WD 996s have a saddle shaped fuel tank that estimates fuel level below half a tank rather than measures it and doesn't detect the fuel level until more than half a tank is in it.
Ha that's very strange but makes sense.
yes I'll fill her up tonight then and see if it realises.
Does that mean that the gauge is not accurate below half a tank normally? or just when it's filled back up? Don't fancy running out of fuel any time soon :?:
Yeah it is an estimate although tbh I think it's quite accurate and errs on caution based on previous mpg etc.
It means you can't really 'splash and dash' when fuel level is low because it won't recognise that any more fuel is in there and then you won't have any idea how much is in there until you fill to over half way...
lol, had the same issue when I first picked up my 996.
Car was on the fumes when I picked up, so needed fuel the first garage only had RON95 so did a splash and dash and it didn't register.
Panicked as I thought it was something wrong, then when I fuelled with 97 RON fuel all the way it worked fine.
Think we all did this early on in ownership! I guess Porsche just never considered that anyone would every put anything other than a full tank of fuel in.
This happened to me yesterday, second time since I've had the car, so not to concerned, however I wondered whether or not as the obc didn't recognise there was sufficient fuel would the ecu 'stop' the car :?
The AWD tank has reduced depth over the front diff, and then drops deeper in front of the diff (ie in front of front axle).
Given the varying price of fuel, the critical value below which the remaining fuel volume is "guessed" is in fact 19 litres.
The AWD models (so C4, Turbo etc and GT3 derivs, which use the AWD's stronger chassis) have additional driveshafts to and at the front (obviously), but this poses problems for the original position/size of the fuel tank.
So AWD models have a reshaped tank, to fit around the driveline and new chassis strengthening structures and driveshaft mountings etc.
The fuel gauge technically only operates above the "flat" of the tank, any fuel level below this is "guessed" by a fuel tank algorithm and sent to the electronic analogue display on the dash.
This means if you are empty and add only enough to fill the lower section of the tank, the sensor is still dry and the gauge won't move (ie under-reads fuel volume)
This might sound stupid, but it is preferable to having the sensor in the base of the tank and over-reading and hence you thinking you have more fuel.
Once enough fuel is added to fill the lower section (ie up to the "flat") the sensor is "wet" and the gauge reads as normal (ie a measure of the entire tank).
This "flat" volume is usually about 1/4 tank (below 19 litres the system actually guesses your remaining fuel from fuelling data, only once it is refilled above this level again is the alogorithm reset and continuous reading handed back to the sensor).
Note: in the diagrams below the "2WD" and "AWD" refer to chassis type, this means as GT models use AWD chassis and hence use AWD tanks.
The issue is the upper and lower segmentation! (the somewhat convoluted constriction between them)
The small lower tank cannot support the use of a contiguous float or capillary sensor all the way to the base (ie it only operates in the larger upper tank).
The lower tank use is estimated by the DME (using fuel injection volumes), but it cannot know if you then added a small amount (<19L total) of fuel.
This is a source reference. Confirm exact model applicability in the original material.
