W Hy My 2003 Cavalier Turns Over But Wont Start Up

What does it mean when a car engine turns over but won't start?

You need:AirFuelSparkIn order to run an internal combustion engine.So, if the car will turn over (starter will rotate the engine), but not start; it means that one or more of these necessary factors is missing.Easiest to check is Air.  Make sure there's no blockage at the intake or air filter housing...or in the ductwork between the two.Fuel is a little more difficult.  On a carburated engine, you can check for fuel flow in the carb.  If there is fuel in the carb, but it's not being ignited by the engine, you will smell fuel.  Same for some injector systems, you can smell fuel in the intake if any is flowing.  Other injection systems might require pulling an injector nozzle to check for fuel flow and pressure.Spark is also relatively easy.  Pull one of the plug wires, stick a bolt roughly the same diameter as the spark plug terminal into the terminal socket on the wire, and hold it (with a pair of long insulated pliers) near the engine block....And prepare for a mildly painfull electric shock if the spark is, in fact, happening.

I have a 2003 Chevy Cavalier. Why am I having difficulty in starting it?

It sounds like you have a bad ignition switch, or a bad ground.  The instrument cluster, and fuel pump relay both ground at the rear of the engine. I would check any bolt or nut at the rear of or on top of the engine that fastens a wire or cable to the engine.  Any other wires under the hood that are grounded to the body, or frame should be checked, cleaned or tightened as necessary.          The ignition switch has a pink wire that should have battery voltage when the switch is in the run position.  If the switch is hard to get to, you could check for voltage at the ignition module fuse, or the instrument cluster fuse, which are probably located in the fuse box inside the car. If you have a test light you can test for power at the fuse with the key on and the car in its no start condition. If no power to fuse the switch is probably bad.      These seem to me the two most likely causes for the problem described in your question, especially the ignition switch. Intermittent electrical failure can be difficult to diagnos, and I could be way wrong here, but this is where I would start.

What is actually happening  when people say, "The car's engine won't turn over?"

When you turn the key (or push a button) to start a car, the battery sends electricity to the starter motor, which "turns the engine". Simultaneously, the fuel system is supplying fuel and the ignition system is supplying a spark to the cylinders, which will ignite and the engine will start running on internal combustion--instead of the starter motor.  This "turning the engine" is literally the turning of the crankshaft, which (by extension) moves the pistons up and down, turns a cam shaft (or several) and opens and closes valves etc. Thus the term, the engine "turning over" means that the internal reciprocating parts of the engine are moving.To say the engine "won't turn over" implies that the crankshaft isn't turning and by (literal) extension, the pistons aren't moving up and down, the valves aren't opening and shutting etc.  The internal reciprocating parts of the engine are not moving. USAGE:  Generally I've used this term to describe the problem or ask this question of someone who is describing to me the symptoms of a car that won't start .  To me, if they say yes to the question, "will the engine turn over ?"  It means that the battery has enough "juice" to turn the starter motor, which is "turning the engine over"...but it won't start and run on it's own.  This narrows down the possible problems to a  probable lack of fuel or spark.Conversely, if they answer, "no" the engine isn't turning over...then the first suspect is a dead or weak battery that doesn't have enough power to turn the starter and the engine.  It could be other things, but from a probability standpoint the battery is the first "suspect" if the engine "won't turn over". Another usage of the term is just to refer to a running engine. Someone might say, "That v12 runs so smooth, you can't hear it turning over." This term is still applicable to modern engines.

What does it mean when a car's battery light turns on while the car is moving (eventually car decelerates and stops)?

The alternator is failing or has ceased functioning. Whereas the engine's torque is usually giving your car constant electricity using the alternator, when it fails to do so the battery's reserved power is then used. Usually the battery is only used to start the vehicle. It obviously has enough power to spark the plugs, but only for so long, especially if you are also running your radio, A/C, headlights, etc. Once the battery is dead, the car is dead.This happened to me more than once. The alternator has a finite life in every car, so there comes a time when it will die, and it will almost certainly not be at the most opportune moment. Recognize signs of this happening before it is too late. Mine was failing for months before it inevitably gave in and I finally figured out what was wrong. A similar issue is if your serpentine belt snaps, the engine is no longer running your alternator, whether it's in good shape or not. This will cause more issues than the car just dying in five minutes- the water pump will cease functioning to cool your engine down and you will eventually overheat it and perhaps irreparably damage the vehicle.There are possibly other things that can cause this issue but this seems by and large the most likely.