I have a 2003, I35 Infiniti. The gas needle all of a sudden stopped working. What could cause this and where can I take it to get it fixed without taking it to the dealership?

Question edited for clarity and toss in some CAPS.

There is nothing that backs up memory. When you disconnect the battery, all memory is lost, which is why it is important not to do it!

You don't tell us the model? Is it a secret? All questions need 'year make model' as the FIRST 3 words.

If your have a 1999 Infinity I30, the ECM Fuse is Fuse 58.

58 10 Engine Control Module (ECCS), Mass Air Flow Sensor, Crankshaft Position Sensor, Idle Air Control Valve (IACV-ACC) Solenoid Valve, Ignition Coils, EGR, EGR Volume Control Valve, EVAP Control System Pressure Sensor

Infiniti i30 (A32; 1995-1999) fuses and relays

Fuse Box Diagrams https://fuse-box.info > infiniti > infiniti-i30-a32-1995-...

Fuse box diagrams (location and assignment of electrical fuses and relays) Infiniti i30 (A32; 1995, 1996, 1997, 1998, 1999).

Infiniti i30, i35 (A33; 1998-2004) fuses and relays

Fuse Box Diagrams https://fuse-box.info > infiniti > infiniti-i30-i35-a33-1...

Fuse box diagrams (location and assignment of electrical fuses and relays) Infiniti i30 / i35 (A33; 1998, 1999, 2000, 2001, 2002, 2003, 2004).

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0430 INFINITI - Catalyst System Efficiency Below Threshold Bank 2

Read more: https://www.autocodes.com/p0430_P1574 INFINITI - ASCD Vehicle Speed Sensor

Read more: https://www.autocodes.com/p1574_infiniti.html

Might change the fuel filter. It might not be allowing enough fuel to the engine.

Don't worry I'm sure you will get the solution of your problem, just check the link I attach
2004 Infiniti I35 Service Repair Manual INSTANT DOWNLOAD

head gasket problem , oil consumption on these car are common! check the pistons maybe you have a blown piston!!

2004 INFINITI I35 subwoofer works some times and sometimes it just does not work at all.

no, idle air control valve is literally to control your idle speed.
what happen when you press on gas? car shakes, RPM goes up, or engine just bogs down?

check the oil strainer

There are so many things that can cause this. What you really need is access to a real scanner, not a code reader, and look at the live data. Look at fuel trim and see what it is doing. If it is taking fuel away, there is something causing an over-fueling condition. If it is adding fuel, then you are actually driving a little lean, but compensating for it by adding fuel with the accelerator, causing loss of fuel economy. Looking at the fuel trim, along with the actual data readings for the MAF, Oxygen sensor(s) and other variables you can have a better idea of what is going on under the hood. Unfortunately, these things are more and more requiring electronic monitoring for diagnostics, unlike years past when we could just about overhaul the car with a screwdriver, a couple of wrenches, a hammer and a pair of pliers. Happy motoring