* Float arm stuck or binding: The float, a small buoyant device, might be stuck or its arm might be binding, preventing it from moving freely as the fuel level decreases. This means it only registers movement when the fuel level is high enough to overcome the binding.
* Faulty float: The float itself could be damaged or leaking, causing it to lose buoyancy and not accurately reflect the fuel level below a certain point.
* Rheostat failure (the variable resistor): The float is connected to a rheostat (a variable resistor). This resistor's resistance changes with the float's position, sending a signal to the gauge. A faulty rheostat, especially if it's failing in a way that only affects the lower resistance range (lower fuel level), will cause this problem. This is a common failure point.
* Wiring issue (less likely): While less probable than the float/rheostat, a break or short in the wiring to the sending unit *could* cause intermittent or partial readings. However, a wiring problem would likely manifest differently than just a limited upper-range reading.
* Corrosion/Debris: Corrosion inside the fuel tank or debris interfering with the float's movement can mimic a binding float arm.
Troubleshooting Steps:
Unfortunately, fixing this usually involves dropping the fuel tank, which is a significant job. Before doing so, you might try:
1. Add fuel: Sometimes a temporarily low fuel level can dislodge a slightly stuck float. See if the gauge responds as you add more gas. (Don't let the tank run completely empty.)
2. Check for codes: Have the car's computer system scanned for diagnostic trouble codes (DTCs). This might point to a specific sensor problem.
If adding fuel doesn't help, the fuel tank needs to be dropped to access and replace the sending unit. It's usually a single component that's replaced as a unit rather than trying to fix the individual parts. This is generally best left to a qualified mechanic unless you have significant experience working on cars.
