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"low fuel" indicator lamp inoperative....


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38 replies to this topic

#1 mwatt

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Posted 14 March 2005 - 12:24 PM

at least I THINK it is....in my 99 Legacy GT and in my wife's 98 Legacy Outback. I could swear that when the Outback was brand new, the low-fuel indicator icon would come on when the guage needle was barely above "E". But now, the indicator in either car won't come on with the guage at "E". (Yes, I've got a bad habit of running on fumes, and somehow I've never run out of gas.) I've pulled the instrument cluster out of both vehicles to inspect and test the bulbs and the printed circuits for continuity; the bulbs are good and the printed circuits have no breaks. Anyone else out there have a concern with their low-fuel indicator lamp?? Exactly when does it, or when should it, come on? Owner's manual indicates that when it comes on , there's about 2 to 2.5 gal remaining in the tank-----and I know that on the '99, I've cut it much closer than that.....

#2 jdw

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Posted 14 March 2005 - 12:38 PM

Are you sure that you are cutting it very close based upon how much fuel you put into the tank?

I'd do a test - carry a few gallons of gas around until you actually run out - see if the light comes on.

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#3 95Leg

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Posted 14 March 2005 - 02:05 PM

You've probably already done this, but does the light come on when you have the key in accessory position or when the car first starts to make sure the basic light works?

My gas gauge does not work (I fill up and reset the trip counter and go for 300 miles) and I haven't cleaned the sending unit as described in previous posts, but when my light comes on, I think I usually end up filling up with 12-13 gallons.

#4 frag

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Posted 14 March 2005 - 02:12 PM

I dont know how it is with the newer models but the low gas light does'nt light up with all the others when I first turn the ignition key to «on». It does light up when I get very low though. I was asking myself the same question a few years ago. I did what jdw recommends, I put a five gallon gas cannister in the back and drove till the light went on. I dont remember the exact mileage but i was amazed at how long and how far I could cruise after the light went on before the engine stopped.

#5 mwatt

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Posted 14 March 2005 - 02:18 PM

Are you sure that you are cutting it very close based upon how much fuel you put into the tank?

I'd do a test - carry a few gallons of gas around until you actually run out - see if the light comes on.

JDW


Well, I've thought about doing that....but then I realized the potential hazard in carrying a partially filled gas can inside a vehicle, or possibly blocking traffic (when the car runs out of fuel) and creating a traffic hazard , AND I've read somewhere that running a newer vehicle out of fuel can damage the catalytic convertor. So I'm weighing out wether or not it's worth the time to diagnose this any further; I mean, the fact that this light works or not is rather nit-picky stuff anyway....Now, I know you're probably saying to yourself "if you're not willing to do the test you'll never get to the root of the problem" but I was kinda' hoping that someone else had seen this happen on their own vehicle???

#6 frag

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Posted 14 March 2005 - 02:31 PM

Well, I've thought about doing that....but then I realized the potential hazard in carrying a partially filled gas can inside a vehicle, or possibly blocking traffic (when the car runs out of fuel) and creating a traffic hazard , AND I've read somewhere that running a newer vehicle out of fuel can damage the catalytic convertor. So I'm weighing out wether or not it's worth the time to diagnose this any further; I mean, the fact that this light works or not is rather nit-picky stuff anyway....Now, I know you're probably saying to yourself "if you're not willing to do the test you'll never get to the root of the problem" but I was kinda' hoping that someone else had seen this happen on their own vehicle???


1)When I did the test I was driving on a country road with very sparse traffic. It would indeed be dangerous to do that in the city or on a crowded highway. I know I was lucky but the engine had its first hickups when I entered the cottage driveway :)
2) I'm willing to learn something new but I dont see how running out of gas could damage the cats.
3) Some pretend that it could harm the fuel pump cause it is cooled by the surrounding gas in the tank. I doubt this very much cause the pump is mainly cooled by the gas going thru it. All the mooving parts of an in tank fuel pump are in contact with the fuel moving thru it, rotor and stator included. I was very surprised when I first saw a detailed diagram of how my fuel pump worked cause I was thinking ELECTRICAL SPARK!. But that's the way it is and it seems the pump is not very often responsible for fuel tanks explosions....

#7 mwatt

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Posted 14 March 2005 - 03:04 PM

You've probably already done this, but does the light come on when you have the key in accessory position or when the car first starts to make sure the basic light works?

My gas gauge does not work (I fill up and reset the trip counter and go for 300 miles) and I haven't cleaned the sending unit as described in previous posts, but when my light comes on, I think I usually end up filling up with 12-13 gallons.


You're right---I did try "turning the key to the start position" as a bulb check--and the light does not come on in either car. The owner's manual for both vehicles has a short section about the low-fuel indicator lamp, but it does NOT say that bulb should light when the ignition is in the "crank" position. But I see your point---because the owner's manual descriptions of all the other warning lamps indicate that all of the rest should light when the ignition is in the "crank" position. When you mention "I haven't cleaned the sending unit as described in previous posts"----I did a keyword search but could not find anything. I know how to R&R the sending unit on these vehicles---but what problem was being corrected by cleaning the sending unit?? Inoperative guage? Inoperative low fuel light? I kind of figured that the low fuel lamp is actuated by the sending unit.........

#8 Smpol19

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Posted 14 March 2005 - 03:15 PM

When you do run it very low how much gas do you put in it? The tank capacity should be in the owners manual somewhere, see how low you are really getting, if you find there are more then 3 or so gallons left in the tank I would say your not getting it low enough. When the light comes on on my OBS and I fill up soon afterwards i usualy put a 13.5 gallons in my 15.9 gallon tank so I'm down to 2.5 gallons.

#9 mwatt

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Posted 14 March 2005 - 03:49 PM

When you do run it very low how much gas do you put in it? The tank capacity should be in the owners manual somewhere, see how low you are really getting, if you find there are more then 3 or so gallons left in the tank I would say your not getting it low enough. When the light comes on on my OBS and I fill up soon afterwards i usualy put a 13.5 gallons in my 15.9 gallon tank so I'm down to 2.5 gallons.


Now this makes sense. Really. I never thought to try this, and should have. You see, I've got little brain left; I'm married with children.

#10 kevinsUBARU

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Posted 14 March 2005 - 08:24 PM

I've put 13.02 in my tank before (13.20) gallon tank. The light did NOT come on. I reset the odometer and drive 300 miles :)

#11 forester2002s

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Posted 14 March 2005 - 08:59 PM

When my 2002 Forester was new, I deliberately ran it dry to see what the fuel gauge meant.

After the 'low-gas' light came on, I travelled another 40km before the engine started misfiring.

And the 'low-gas' light does not come in with all the other test lamps, during the 'crank' cycle. What were the Subaru designers smoking, when they arranged it this way?

#12 TheBrian

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Posted 14 March 2005 - 10:24 PM

I've checked a few times, and my gas tank accepts very nearly 51 L of fuel when the idiot light has just come on. Subaru says I've got a 60L tank, and that the light comes on when 9L remain. So I say with confidence that my idiot light is very accurate.
Though the fuel gauge is one pip below E at that point.

My guess is that the idiot light would come on if you ran it down farther.

#13 Gnuman

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Posted 14 March 2005 - 11:08 PM

When I get real low on fuel, my idiot light plays "peekaboo" with me several times before coming on and staying on. never ran dry. Most I've had room for in the tank is 14.5 gal in a 15.8gal tank. The indicator light is seperate from the guage senders (there are two of them), and is usually more accurate. As for how it could harm the cat? well this is a stretch, but if the battery runs slow enough to not be able to fire the spark plugs (some electronic ignition units are picky about voltage levels), but the injectors are still pumping gas, then you are throwing raw fuel down into the cat, and when you finally get a jump and get the engine started, then that raw fuel burns in the cat and cooks it. Like I said, a stretch. . . :rolleyes:

Only harm I have ever heard of from running dry was that you could burn out the pump or drain the battery (while trying to get gas to the injectors) on a dry system. This was only mentioned on American Iron, and I'd be willing to bet that our Subies are made of sturdier stuff than that. . . I mean, this was told to me when 100K miles was considered a long time for a car to last. . .

#14 Commuter

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Posted 14 March 2005 - 11:51 PM

As the sending units start to go on these cars, the gauges seem to read lower and lower.

When I got my 97 OB, the light would come on with the needle a touch above E. Now, the needle is well below E when the light comes on. However, It usually takes right around the same 52 L (of 60 L total tank capacity) to fill up. Somehow, the light remains fairly constant, but the needle drifts.

This summer, if I find the time, I'll probably clean up the sending units.

Commuter

#15 mwatt

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Posted 15 March 2005 - 09:23 AM

As the sending units start to go on these cars, the gauges seem to read lower and lower.

When I got my 97 OB, the light would come on with the needle a touch above E. Now, the needle is well below E when the light comes on. However, It usually takes right around the same 52 L (of 60 L total tank capacity) to fill up. Somehow, the light remains fairly constant, but the needle drifts.

This summer, if I find the time, I'll probably clean up the sending units.

Commuter


Just to make sure I understand you: you're saying there are two sending units--one for the guage and one for the low fuel lamp? If that's the case, are BOTH of those accessible thru the panel under the back seat?

#16 Commuter

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Posted 15 March 2005 - 01:05 PM

Just to make sure I understand you: you're saying there are two sending units--one for the guage and one for the low fuel lamp? If that's the case, are BOTH of those accessible thru the panel under the back seat?

I don't have personal experience, but my understanding is that their are 2 units due to the "hump" that the driveshaft puts in the fuel tank. There is one on each side. How they are configured to the light and the gauge, I have no idea. I can't explain why the gauge acts up, but the low level warning light still works ok.

Commuter

#17 NOMAD327

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Posted 15 March 2005 - 01:15 PM

the low fuel light probe and the electric pump are on the passenger side along with a float type sender for the gauge. The driver side has a smaller float type sender and a suction screen. The passenger side unit has a jet type pump that draws the fuel from the driver side. The low light probe should not vary with cleaning, but the two float type senders definately do start to err in the low direction over time as they get dirty.

#18 Martinjmpr

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Posted 16 March 2005 - 11:21 AM

I just noticed the same thing on my 99 OBW. On the way down to Florida, the light did come on (when the needle was just below the E). On the way back, it didn't come on, no matter how low the needle went. I wasn't sure if it was just that I hadn't run the tank down low enough, but when the car started coughing and bucking due to starvation (fortunately, I was about 2 blocks from a gas station) I realized the low fuel light just didn't work. I still haven't decided if it will be worth it to get the light fixed, since I normally use the gas gauge and the odometer to determine when I need to fill up (typically around 325-350 miles.)

#19 Cougar

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Posted 16 March 2005 - 12:34 PM

Commuter is correct about the sending units working in parallel with each other and the tank separation. I'm guessing that the warning light comes on when the sender voltage goes below a certain level. I haven't really checked the circut out enough to know for sure.

#20 Setright

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Posted 16 March 2005 - 03:07 PM

Not quite on topic, but anyway: I noticed my 1990 Legacy light did what Gnuman describes, it would come on and off as the level lowered and the gas sloshed around.
In my 2000 Impreza the light is "latched" and stays on once it has been activated.

#21 Tiny Clark

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Posted 17 March 2005 - 02:02 AM

I am looking at the only schematic I have of the fuel gauge system.

It shows the two sensors are in series with each other, comprising of variable resistors.
This resistance is fed into a CPU located in the instrument cluster. It shows the outputs of the CPU going to the light and gauge. Maybe once the resistance reaches zero, or very close to it, the light is supposed to come on.

Doesn't make sense to me doing it this way, but I run into this all the time on our airplanes.

Maybe someone can verify that fact that there are only two wires coming off the sensors. If not, I don't know where the hell they got this diagram from.

#22 Forester_Ranger

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Posted 17 March 2005 - 06:07 AM

I ran out of gas for the first time on my 98 Forester a couple months ago. Because i thought there was enough fuel since my Low fuel light hadn't come on yet. Even though I was already below E and it usually comes on right before or on E. I was only a couple miles from a gas station i was planning on fueling at and my Low fuel Warning light came. Immediatly after the Low Fuel Warning light came on the car died. I thought Geez thanks for the warning. just a couple weeks ago I was inspecting my drivetrain parts under the car. I noticed I had a pretty nice size dent on the passenger side of the fuel tank. I think this may be the reason my Low Fuel warning is inaccurate. ever since I ran out of Fuel I consider the 1/4 Full mark as Empty to insure I don't run out again.

#23 NOMAD327

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Posted 17 March 2005 - 06:25 AM

there is a separate probe for the low fuel light and it is part of the passenger side unit

#24 Tiny Clark

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Posted 17 March 2005 - 07:58 AM

Thanks nomad. Wasn't sure if I could trust that diagram, and can't even remember where I got it.

#25 mwatt

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Posted 17 March 2005 - 10:11 AM

there is a separate probe for the low fuel light and it is part of the passenger side unit


OK--are the tank units accessible only from under the vehicle or are they accessible thru the panel under the rear seat?




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