low fuel light issue - new twist?

[lil_buddy]

So the low fuel light came on this morning, but the tank is like 3/4 full which is confirmed by the gauge, my ultragauge, and my estimation based on the number of miles travelled since filling it on Tuesday.

I've read threads about the light never coming on with or without the gauge being off, but not this.

Insights?

[fdryer]

Feel like dropping the tank to check on a faulty fuel level sensor?

[lil_buddy]

is it part of the fuel pump? can i just get a new fuel pump?

[fdryer]

Pump and level sensor are assembled into a module. Both can be replaced or as most issues are failed pumps the old level sensor is retained and a new pump grafted in. If the pump is working then the level sensor may be replaced. You won't really know until checking connections before dropping the tank for exploratory surgery. Who knows, maybe the float ruptured and filled up with fuel, sinking the level or partially filled..............................

[lil_buddy]

Originally Posted by fdryer

Pump and level sensor are assembled into a module. Both can be replaced or as most issues are failed pumps the old level sensor is retained and a new pump grafted in. If the pump is working then the level sensor may be replaced. You won't really know until checking connections before dropping the tank for exploratory surgery. Who knows, maybe the float ruptured and filled up with fuel, sinking the level or partially filled..............................

This was a little difficult for me to follow - I guess because "checking connections" is vague to me - no idea what's going on inside the fuel tank - things can rupture? - the level is sinking but the gauge is reading correctly - so confused.

What I was thinking when I asked the previous question: I have that pesky '97 check valve issue which can only be fixed by replacing the fuel pump (right?). So if I replace the fuel pump will it also fix the new issue. The answer is no - I have to get a new level sensor(right?)

What brand of these things should I get?

I am afraid the ACDECLO or Delphi parts will have the same check valve defect because one of them is OEM - not sure which.

BTW - the light went out.

[fdryer]

If you use the trip odometer to reset and log fuel mileage then this can be the back up for an intermittent fuel level sensor. A recent member had his die out completely (either here in the S-series or the other models) and dropped his tank to find a pinhole leak in the float. Checking replacement parts prices found them ridiculously high so scouring around turned up a Ford(?) float that fit for a few dollars and used it. A float is similar to most old school toilet bowl mechanisms using a lever with a hollow plastic or brass ball on one end while the other end operates the water valve - hinged at the valve, when flushing, water drains from the water tank, the float drops as it floats on the decreasing water level (flushing the toilet bowl) opening the water valve that starts feeding water into the quickly draining tank. A flapper valve closes and seals the tank from draining and as water fills the tank the float moves upwards until a predetermined level is reached where the valve is closed by the float arm. The fuel tank level sensor operates the same way to use a very low voltage that varies according to fuel level. The float on the arm may be damaged or the voltage circuit card is faulty from age. Google fuel tank level sensor and/or toilet float mechanism for a tutorial.

The fuel pump is a totally separate subsystem of the fuel pump module. There are pictures and drawings here from postings or search rockauto.com for parts to see yours. Replacing the fuel pump will not correct an intermittent fuel level sensor. It may not correct the fuel check valve issue as no one has proven a new replacement pump isn't the same as the old one, making it possible to inherit the same issue. Its easier to deal with the issue with a simple start up procedure with a delay between ignition ON and START.

As long as the fuel level sensor works then it may not be worth dropping the tank to repair it until it fails completely. The same with troubleshooting the connections to the tank as the wire harness and connections are on top of the tank. If you are not familiar with electrical/electronic wiring and reading wiring diagrams/electrical/electronic schematics, this may be beyond your ability level.

[td1238]

Why are we suggesting checking/replacing the sending unit when the gauge reads 3/4, and it has been confirmed that there is 3/4 a tank of gas? The sending unit is fine. Something is wrong with the circuitry that operates the 'low fuel' light. As I have never disassembled the gauge cluster to see just what this circuitry is, I can't say for sure what it is, but something with a bit of time delay turns on the light when the gauge receives a voltage that is consistently at a certain level that keeps the needle at or just below 'E'. Seems that this circuitry isn't doing what it's supposed to.

The sending unit is merely some resistance material printed onto a board, and a wiper that wipes over this resistance material. Two wires are involved. If the gauge reads 3/4, and the tank is indeed at 3/4, then there's nothing wrong with the sending unit.

[OldNuc]

The low fuel light is turned on by the PCM and if the signal from the sender does not drop low enough then the light does not come on. There is nothing in the cluster that turns on the light.

You can replace the sender by disconnecting at the inline connector and substituting resistors.

full = 18 ohm
3/4 tank = 68 ohm
1/2 tank = 113 ohm
1/4 tank = 163 ohm

[td1238]

Ok, so then something in the PCM is malfunctioning. There's nothing wrong with the sending unit if the gauge reads what's really in the tank.

[OldNuc]

Wrong, if the sending unit does not reach a high enough resistance then no light. The gauge it notoriously inaccurate and all you know is there is gas in the tank until you actually calibrate the gauge by filling the tank when the level is at the major divisions and noting the fuel added.

[off-track]

Originally Posted by lil_buddy

I have that pesky '97 check valve issue which can only be fixed by replacing the fuel pump (right?). So if I replace the fuel pump will it also fix the new issue.

If you have the 97 hard start problem just replace the FP assembly and it should take care of both problems. The current recommendation is to avoid Airtex.

[OldNuc]

Carter is the preferred assembly and would be easy to test out of the car. Just connect up the sensor wires ONLY and turn key to on and slowly lower float. While the unit is out verify that the tank bottom is not bowed up preventing the float from dropping to the point the light will come on. Do be sure to test it and verify adequate drop when installed while tank is out.

[saturnsctwo]

how low does the fuel in the tank have to be to turn on this light anyway? i thought i would'nt make it home today as my needle was just a hair above empty. isn't there like a gallon of gas still in the tank when the needle first points to empty?

[saturnsctwo]

where is this low fuel light on 2001 sc2? i don't think i ever even seen it nor paid any attention to it if i did...

[OldNuc]

It is not calibrated in actuality. There is supposed to be 1 to 1 1/2 gallon when the light comes on but if the bottom of the tank has bowed then you lose.

Using the bottom of the tank is hard on the pump and you really should stay out of bad neighborhoods at night as you will be walking a lot.

[lil_buddy]

my low fuel light comes on after I have spent 10 gallons - consistently & accurately.
Tank capacity is 12.2gallons.

[off-track]

Originally Posted by lil_buddy

my low fuel light comes on after I have spent 10 gallons - consistently & accurately. Tank capacity is 12.2gallons.

You're lucky! That's one thing that's always bugged me. I've got records going back 5 years, have several fill-ups over 11 gallons and, am on my third pump/sender. The ONLY time I've ever seen the "low fuel" light is during the initial gauge self check on start-up.

[saturnsctwo]

Originally Posted by off-track

You're lucky! That's one thing that's always bugged me. I've got records going back 5 years, have several fill-ups over 11 gallons and, am on my third pump/sender. The ONLY time I've ever seen the "low fuel" light is during the initial gauge self check on start-up.

where are these lights anyway? i got a 2001 sc2. yoiur dash is similer to mine...

[off-track]

Originally Posted by saturnsctwo

where are these lights anyway? i got a 2001 sc2. yoiur dash is similer to mine...

Reference this post as SF won't let me upload the same image twice.
http://www.saturnfans.com/forums/sho...90&postcount=4
It should be close. #3. Mine says "low fuel" but eSI shows a pump icon for a Gen-III.

[saturnsctwo]

ah ok i seen it today in the lower left. the bulb works. i was lookig for a light spelled out low fuel;, but on mine it just shows a fuel pump.