My 2000 dodge neon isnt starting

Dodge codes p1684
For Chrysler vehicles, a code P1684 represents a battery disconnected within last 50 starts. Although the code signifies a battery-related issue, diagnostic codes do not tell you how to proceed with repairs. It is the job of a trained professional to further diagnose and repair the problem.

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Nikki is the engine light on, are there any codes,have you had a tune up or any other work done lately.when you say it won't start when warm(do you mean engine will not turn over, or does engine turn and refuses to fire.
If I had to guess failing fuel pump, they tend not to build fuel pressure when ran a while(warmed up) and when left to cool build somewhat better pressure.
press the helpful button

Is Your Fuel Pump Going Bad
How do know if its fuel filter or fuel pump that is causing the problem
How To Diagnose Fuel Pump Failure EricTheCarGuy
http://www.clarks-garage.com/shop-manual/ts-01.htm#hot-start

that code is set when you disconnect the battery. It can happen if you have bad connections. Sounds like you have a lot of things wrong.

CODE P1684 - BATTERY HAS BEEN DISCONNECTED.LOOK FOR LOOSE BATTERY CONNECTIONS. ARE BATTERY ITSELF HAS CELL PLATES SHORT INSIDE OF IT. CODE PO171 - FUEL SYSTEM LEAN. CODE PO462 - FUEL LEVEL SENSOR NUMBER 1 LOW INPUT. ALL YOUR PROBLEMS HAS TO DO WITH CODE P1684. CHECK BATTERY HAVE IT LOAD TESTED AND CHECK BATTERY CABLES FOR TIGHTNESS.TO KEEP FROM LOCKING OUT RADIO TURN IT OFF FIRST BEFORE YOU DISCONNECT NEGATIVE BATTERY CABLE.

The P1684 code simply means that the battery has been disconneted within the last 50 starts.
P0551(power steering pressure switch)

P1684 Driver 5 Line 4

P1684 Battery Disconnected Within Last 50 Starts
P0406 Exhaust Gas Recirculation Sensor A Circuit High

P0406 can mean the EGR sensor or valve is not functioning properly.

P1684=The battery has been disconnected within the last 50 starts

P0171=System Too Lean Bank 1,this is an oxygen sensor

P0340 Camshaft Position Sensor "A" Circuit Bank 1 or Single Sensor

P0700 Transmission Control System (MIL Request)

The code P1684 is real easy. The computer is stating that the battery has been disconnected within the last 50 starts.

Hey, Code 0700-Transmission Control System (Malfunction Indicator Light Request)
Code 1684 -Battery disconnected during last 50 starts