1997 honda civic hx. I recently restored the car and replaced the fuel pump. Four days ago I filled the car full, and the gauge read full, but the low fuel indicator light comes on. Today, the gauge is reading under the full line. So, I turned the key ignition to the "on" position and unplugged the three wire connector to the fuel low level sending unit and watched the light go out and the fuel gauge moves towards empty. I plugged it back in and the light comes on and the gauge reads what it did before.

 

It's broken.

 

Maybe a short to ground in the low fuel light wire in the 3P connector. Check that first.

 

The gauge and the light are separate systems. They have a separate sensor and a separate wire (though both are in the same plug leading to the tank). If the light goes out when you unplug at the tank, the problem must be inside the tank.

 

You have short in the thermistor wiring. Remove the fuel guage sending unit and check that where the wire of thermistor is touching the metal rod. My thermistor wire insulation also worn out. It will be touching somewhere. If that is not the case then thermistor is faulty. You can replace only the thermistor. If you want I will send you the link.


I am talking about this wire. If it touches the metal rod, then light will be always on. Look how worn out mine is.

 

I will not be in favour of replacing the whole fuel gauge sending unit and wasting your money as your fuel gauge is working properly. The problem is with thermistor or its wiring.



Here it is how to remove the unit.

 

Thank you all that provided positive and HELPFUL diagnostic possibilities to this issue. I will value everyone’s feedback and utilize this information to try and rectify this problem. More to follow...

Cheers.

 

I finally removed the fuel sending unit. The thermistor seems fine. When I removed the unit the gauge meter works perfect when connected and Ignition is in the II position. But the Low indicator light does not go off when the meter is moved to the full position, I can’t make sense of this; but when I apply a jumper to the 3 pin connector the gas gauge light indicator gets brighter, but when I remove the jumper it dims down.
I’m sorry but for some reason I’m not able to upload photos.

 

this mean your thermistor is bad. You can get any low fuel thermistor for any car/bike from ebay. Or if you want to stick to oem then you need to replace the whole sending unit.

 

Thermistor is activated by temperature not position. When there is some gas in the tank the thermistor is submerged in gas which keeps it cool. When the tank is nearly empty the thermistor is not submerged in gas and it heats up, which causes the light to come on.

Testing outside the tank can be done by measuring ohms or when you first turn the key on the light should be off at first then come on after a few seconds as the thermistor heats up. If it comes on instantly something is wrong.

Note that this system depends on the characteristics of the bulb specified. If you have replaced the bulb in the dash with an LED or a different type of bulb it will not work, it may stay on all the time.

 

Ok so first thing is the float has nothing to do with the low fuel indicator. it is only for guage. Secondly after removing the connector if the light is still on even if it is dim this means there is somewhere short in the wire. It maybe inside cluster or the wiring leading to the cluster

 

Thank you all for support and feedback. I removed the gauge cluster and swapped an OEM bulb in place of the LED that was in the “low fuel indicator” spot. That fixed the problem on the “low fuel indicator” consistently staying on. It obviously had something to do with the LED bulb and voltage. Thanks again HT !