Fuel Full, Low Fuel Light

[Chris3991]

Just installed new fuel pump/sender unit from DMCMW. Installation was relatively painless. Upon starting the car after completion and filling it with gas at the local gas station, the fuel gauge showed full and I was relieved that many of my problems were solved. After returning home we replaced the fuel pump access panel in the trunk and were just about to load the spare tire when I noticed the fuel gauge read empty and the low fuel light came on. All of the electrical connections were still in tact and not loose in anyway. I started the car a couple of times in case something in the electronics needed to be reset but to no avail.

So now I have a new fuel pump and sender, a full tank of gas, a low fuel light, and a gauge that is reading empty.

Any thoughts?

Cheers

[1batt4u]

You bought the new fuel pump/sender unit combo? NEW Integrated pump sender combo kit.

[Jonathan]

I first read your post thinking it said the idiot light came on yet the needle on the gauge showed full. You're actually saying though that both the gauge and warning light are indicating low, right? That actually might be easier to resolve than if one was right and the other was wrong.

I haven't seen the inside of these new units, but are they still a mechanical float that bobs up and down? Could it be that yours got stuck in the low position when you installed it? Or whatever it is that the sender uses to get the signal that there is no fuel in there, perhaps something is tricking that sensor and fooling it into thinking there is no fuel in the tank? I am thinking for example if it was optical in some way, there could be some piece of debris blocking the sensor, kind of like your garage door light. Not sure if they are made that way or not, so just a thought.

[jmettee]

Sounds to me like something in the sending unit (or the mechanical float) broke. Since BOTH the gauge & the light show empty, it tells me the the sender is sending that as the output. If it were just 1 or the other, I would suspect a possible connection or wiring problem. I believe the only way the low fuel light comes on is receiving voltage signal THROUGH the fuel sender circuitry.

[DMCMW Dave]

Sounds to me like something in the sending unit (or the mechanical float) broke. Since BOTH the gauge & the light show empty, it tells me the the sender is sending that as the output. If it were just 1 or the other, I would suspect a possible connection or wiring problem. I believe the only way the low fuel light comes on is receiving voltage signal THROUGH the fuel sender circuitry.

This is correct. On the new system the low fuel light is electronically derived from the float output (not a separate switch). If it reads low AND the light is on, either the float is stuck down (not likely if he filled the tank and it read full at first), the float has become detached from the arm, or a wire has broken off the sender. I have not seen any of these failures but knowing how it works I can surmise. Failure of the electronics unit would more likely cause an erroneous "full" reading.

Quick check - remove the tank plug where the sender used to be and take a look. From that hole you can see if the sender float is moving freely and that everything is in place. You can use a wire or hook tool to carefully lift the float arm up and see if anything changes. Don't force anything.

[David T]

The proper thing to do is to call the vender you bought it from and let them know you are having a problem. They are the only ones that should be giving you advice because they are the one that will have to replace it if it is found to be defective. You should NOT try fixing it unless that vender specifically instructs you. If you touch it without their assistance they can claim it is bad because you did something on your own. New parts are not supposed to fail, especially so quickly, and if they do they should be exchanged, no questions asked. It is not the customer's job to figure out what went wrong, only to make sure it is the new part that was just installed.
David Teitelbaum

[Ron]

I believe the only way the low fuel light comes on is receiving voltage signal THROUGH the fuel sender circuitry.

Actually, voltage is already at the light -- the sender supplies ground to complete the circuit and make the light come on.

It is not the customer's job to figure out what went wrong, only to make sure it is the new part that was just installed.
David Teitelbaum

...and to do that, remember that unplugging the unit at the factory plug and grounding the Light Green/Orange wire should make the Low Fuel Light come on, and, grounding the Green/Black wire should make the Gauge show full. (See factory setup here) So if you unplug the the unit and the gauge drops and the light goes off, it is the culprit (if tank full). Otherwise, you need to look for something grounding both wires (which would be very odd).