Why did the fuel gauge on my 2007 Toyota Corolla suddenly fail?

run the fault codes
reasons for not starting are
broken timing belt /chain
cam/crank position sensors wot working
immobilizer inoperative
problem ignition control module
failed coil/s ECM fault
no fuel pressure ---faulty pressure regulator
faulty pump
gear not in neutral or park

Have a look on the link below. It may be a problem unique to your particular model of car:
http://repairpal.com/fueltemperature-gauges-may-fail-or-read-maximum-at-all-times-924
Fuel temperature gauges may fail or read maximum at all times Toyota...

Fuel sending unit is malfunction. (Not working) Replace whole new one include fuel pump.

Mai Lor

The most likely cause will be the sender unit in the fuel tank has failed, you will need to get an auto electrician to test the resistance of the sender unit.

{: ) If the fuel tank is actually low in fuel, this will be a normal thing. You can also check for fuel leaks. But for example, the last time you remembered it was at half level and after driving for a few miles, you made a stop for some reason, and off course you were expecting that you still have more fuel remaining to take you home or elsewhere. When you start the car again, the gauge suddenly reads empty. This is a classic symptom of a failing fuel level sensor that needs to be replaced.
An engine light may or may not come on. A better option is to check the vehicle using a scan tool to retrieve and clear codes that may have set, Usually, when the engine computer detects a fault in the fuel system, it will set a code, and the fuel gauge will default to zero regardless if your tank is actually full or half. The scan tool can also monitor and determine if the fault is from your gauge, the fuel level sensor, or from the engine control module.
Wiring problems, although very unlikely, can be a possible cause too especially if the vehicle was previously serviced or repaired, and some wire or connector could have been knocked off accidentally or neglected afterwards.

If there's a hum on the throttle body, the throtle position sensor is at fault.

The fuel sending unit in the tank is going bad,it is a float,and it is failing,to repair,it must be replaced,removal of the tank is required.

You weren't low on gas - your fuel tank sending unit is failing and needs replacement. It's inside the tank and usually can be replaced without replacing the fuel pump as well - don't get suckered into that.

find the wire that goes to temp sender and apply earth to it turn ignition on the temp gauge should read hot if it does replace water temp sender if gauge dose not move gauge needs replaging