My 2000 tundra has 77,100 miles on it, at about 70k my light started to not work, and now will not work. The bulb works fine as I tested in the check engine hole. I am wondering if the sending unit is going out, or if it could be a bad ground or fuse. any suggestions
**Warning!!!** Be very very careful when working around the gas tank! Obviously, do not smoke or allow any sources of heat near the tank or fuel sender, and do not use an incandescent light source while working on the fuel system because a dropped bulb can cause a spark. Work in a well-ventilated area.
The fuel level has to get pretty low for the low fuel light to come on. Basically, the sensor has to dry out for the light to come on.
The low fuel light sensor is attached to the fuel level sender. If you remove the fuel level sender from the tank and re-attach it to the wire harness and turn the ignition switch on, the low fuel light should come on. If it does, then you may not be letting the fuel level get low enough for the light to come on.
It helps to have a repair manual or electrical wiring diagram to determine which terminals in the fuel sender connector are for the low light sensor. To check the circuit, disconnect the fuel sender from the wire harness and short the terminals for the low fuel light sensor. If you look at the wire harness side of the connector with the lock tab on top, I *THINK* there will be 3 terminals on top and 2 underneath, and I *THINK* that upper left and upper right terminals are for the fuel sender. I recommend that you confirm which are the correct terminals before shorting terminals, due to the possibility of sparks. If you short the wires and turn the ignition switch to the on position, the low fuel light should illuminate. If the low fuel light does not illuminate, the problem is in the bulb, wire harness, or combination meter.
If the low fuel light does illuminate when you short the terminals, remove the fuel sender from the tank, ground one of the terminals for the low fuel sensor, and apply 12 volts through a 3.4 watt bulb to the other terminal for the fuel sender. With the low fuel sensor dry, the bulb should gradually illuminate. With the low fuel sensor immersed in fuel, the light should go out.
I'm surprised that you didn't tell him how bad an idea it is for him to drive his vehicle until the light comes on though Ray. It causes extra wear on the fuel pump or something like that doesn't it?
It is a bad idea to drive until the low fuel light comes on, but not really because of extra wear on the fuel pump. When the tank gets that empty, especially in cold or humid conditions, condensation can accumulate in the tank, which can foul the fuel filter and injectors and cause drivability problems. The fuel pickup is lower in the tank than the low fuel sensor, so the pump is still drawing fuel and being lubricated. If the tank is low enough for the fuel filter to run dry, then extra wear on the fuel pump may result, besides the hassle of being stuck somewhere.
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