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2005 Legacy 2.5i Wagon 4EAT; 2005 Forester XS 4EAT
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Discussion Starter #1
I've run down to almost the empty line, and my light doesn't come on. It doesn't come on during startup, either.

Does this sound like a bad bulb? If so, which type of bulb does it take? Should I just see what my Subaru dealer has?
 

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02 OBW
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131 Posts
I'm guessing by your join date that you're fairly new to this subaru? If so -

The light doesn't come on during startup, and I doubt it would be burned out - but I'm not sure if there is a way to test it.

The light won't come on until the fuel is very low, touching or on the E mark - the light is usually a lot more accurate than the needle (which gets more and more inaccurate with age it seems).

I've driven my 4-cyl '02 Outback 30 miles once the light comes on, it probably had a few more left, but I didn't want to find out the hard way. Best bet is to run it down near E and get a gas can and drive some more. :)
 

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06 OBW 2.5, 05 Forester, had 03 H6 OBW
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I've run down to almost the empty line, and my light doesn't come on. It doesn't come on during startup, either.

Does this sound like a bad bulb? If so, which type of bulb does it take? Should I just see what my Subaru dealer has?
Mine on my '03 H6 doesn't come on except when the needle is a little below E.
You should be getting (ate least) a bit over 300 miles (315? 330?) before it comes on.

I have had the light turn on, driven for 15 miles or so, maybe 20, and it still hasn't taken 14 gallons.
 

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03 H6 OBW & 06 WRX Sportwagon
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you could carry a gallon of clean fuel around for the next few trips.

just in case.
 

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2005 Legacy 2.5i Wagon 4EAT; 2005 Forester XS 4EAT
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672 Posts
Discussion Starter #6
Thanks all. I'll save the $12 and not get a new bulb from the dealer.
 

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01 Outback H6 VDC, 97 GT wgn w/ ej22, 98 OBW w/ej22
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your tank holds 16.9 gallons. if you are only pumping 13 or less when the gauge says E then the gauge is wrong. my light comes on around 2.5 gallons left.

keep track of your fuel mileage for a couple of tanks, and then multiply that times 16. that is your ''miles per tank'' figure with 1 gallon to spare.

happy motoring.
 

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^ what he said. My light comes on when the tank has 3- to 2.5 gallons left in it WAY long after the gauge has fallen past the E. My old 2001 was this same way also
 

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I'm surprised that the low fuel warning light doesn't come on when the key is at ON but the engine isn't yet started, but given the number of confirmations here, I guess that must be correct for the 2nd generation OBs. (It does come on in my 2007.)

The warning light is controlled by a cpu that's part of the combination meter. It measures the resistance of the two fuel tank level sensors, and when the total resistance rises to a predetermined level, the light is turned on.

How interested are you in testing the function of the bulb without risking running out of fuel. I think there is a way. (Appreciate comment on this from others.)

I've attached the wiring diagram for the fuel gauge system; this is for 2002, but I have verified it's the same back to 2000.

The technique would be to lift the rear seat bottom to access the floor hatches to the fuel tank. Remove the left side hatch, which is over the sub-level sensor. Disconnect the two-wire connector (R59 in the diagram) and connect a variable resistor with a range of 0 to 100 Ohms across the connector. (Make sure there's no chance of shorting or grounding any connections.) Then turn on the ignition and increase the variable resistor slowly. As the resistance increases, the fuel gauge should go down. At some point the combined resistance of the variable resistor and the other fuel level sensor will reach the point where the gauge is at E and the light should come on. (The system might delay triggering the light to avoid false positives due to normal fuel shifting whe driving, so the test should be done slowly.)

Explanation: The main fuel level sensor varies from near zero Ohms when full to around 53 Ohms when empty. The sub-level sensor varies from near zero Ohms when full to about 40 Ohms when empty. When the tank is "empty" the total (maximum) resistance of the two sensors in series would be in the 90 to 95 Ohm range. This should be the point where the light is (or has already been) turned on. Assuming that the test is done when the tank in fact is not empty, the main sensor will be somewhere above zero Ohms, so it shouldn't take the full 100 Ohms of the variable resistor for the gauge to drop to E, and for the light to come on.

If the light doesn't come on when the variable resistor is at it's highest resistance (100 Ohms) it might indicate the light isn't working. The bulb would be the first thing to check.
 

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2011 Tacoma TRD Sport Double Cab Long Box
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The only time my light ever came on was at something like (if memory serves correctly) 340 miles and ~13.5 gallons, and it had just barely lit then.

If it's really a 16.9 gallon tank, I don't think I'd have the nerve to find out! I've never put in even 14 gallons before.
 

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2005 OBW 2.5L, 1989 Subaru Justy, RIP Blu
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The E line on Blu is 10 gallons.

The reason it doesnt come on (and they usually donty) on startup is because it is a thermisor and not a switch. It is sensing the temp of the air around it. Gasoline being colder it doesnt trip, air being wramer it will. They are more accurate in warmer weather then sub zero weather, but still wont get you stranded.

Take a gallon gas can, and just drive untill the light comes on. I bet it will wome on around 14 gallons consumed, maybe 14.5.

How much gas does your car take on "empty"
 

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The reason it doesnt come on (and they usually donty) on startup is because it is a thermisor and not a switch.
That's correct for pre-2000. However, the thermistor control for the low fuel light was replaced by the custom cpu in the instrument panel as of MY2000.

Attached is the 1999 wiring diagram where the circled thermistor is seen in the fuel gauge module at the lower left, and that is connected back to the low fuel warning light in the combination meter. There's nothing like that in the 2000+ diagrams -- see attachment in post#9 above.
 

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