Having an engine that cranks but won't actually start can be incredibly frustrating. However, there are a number of easy fixes and troubleshooting steps that may help you find and fix the problem. Also, the following steps assume that you have already checked to see if you have a faulty starter. The starter may be faulty if the engine cranks inconsistently or the started itself makes strange or grinding sounds when you attempt to start your vehicle.
In extremely cold weather, if your fuel is low, it can be hard for your car to start up. This can mean that your fuel has become less liquid than usual or you just don't have enough fuel for your car to start as a cold car require more fuel to start and run than a warm car would. If your fuel stores are very low, the weather is well below zero (including wind chill), or your car has been having trouble starting up in cold weather recently, this may be your issue. Thought it may still be wise to go ahead with the rest of your checks to make sure there isn't another, obvious and more easily fixed issue.
Newer cars have keys that communicate with them in order to start. A faulty key or key without these capabilities means that it may not start. However, in these cases, the engine will typically not crank.
Do you smell burnt rubber or fuel? Is there smoke or black soot? Both of these can be signs of a leak or flooding. Make sure to clean everything you can and perform proper maintenance to correct these issues before proceeding.
If your check engine or service engine soon light is on, check the codes. Even if neither light is on, your car may still output certain maintenance codes for things it knows are "wrong" but that it hasn't realized are preventing things from working correctly. As your car won't start and if you don't have a digital code reading device handy, there is a way to read codes "manually" and this method is typically outlined in your vehicle's owner's manual or on its manufacturer's website.
After checking for error and maintenance codes and finding none, check your battery. Is it corroded? Are all of the connectors and wires intact and in good shape? If not, can you repair, clean, or replace them? Once you have done so, it wouldn't hurt to see if that has fixed your issue. Corrosion can lead to more issues than most people would think.
If no damage is found on the outside, check the function of the battery. It may not be dead, but it could be dying. Had your vehicle been slow to start before it stopped completely? If so, that is a sign that your battery has been dying for quite a while. Even if everything was fine, a battery can lose functionality quite quickly once it has reached the three-year mark and even faster after five years.
Occasionally and advanced "anti-theft" security system can prevent a car from starting. If you have recently had a small car accident, fender bender, bent your mirrors, hit your car with anything, or pressed the "panic button" your security system may have engaged and cut off the fuel supply.
Wiring can be chewed overnight causing untold damage and frustration but it's an easy thing to spot and should be inspected regularly anyway. Sensors, especially temperature sensors, can become blocked, dirty, or corroded and will need to be cleaned or replaced id the damage is too great. Hoses should also be inspected. Even a slow leak could be the culprit.
Filters, both oil and air, can become blocked and prevent a vehicle from starting. They may also be installed too tightly and cause an error with another system or read as blocked even when they are new or clean.
Fuses may blow out or become damaged and need to be replaced. Any fuse could be the problem, so make sure to check them all. If one fuse is damaged, be sure to check the others. There could be more than one at fault.
Much like fuses, spark plugs need to be individually tested to ensure they are in working order. However, spark plugs may also be damaged or weak, rather than simply non-functional. You need special equipment in order to safely test spark plugs.
Testing your fuel pump and other systems once your car refuses to start will take specialized equipment and knowledge. If you have made it this far and none of the above steps have yielded any results, you may have to seek expert help in order to proceed safely through the rest of your systems.
However, you can test for signs of a dead fuel pump. In order to do this, you should be able to turn the car on, without turning the key far enough to make the engine attempt to turn over. Listen closely as you do. Do you hear the same sounds you usually do? Typically, there will be a light buzzing type sound coming from the fuel pump, briefly. That means it's working. If there is nothing but dead silence, you may have a dead fuel pump.
If your engine cranks but doesn't start, any number of things could have gone wrong. Still, most of these fixes are relatively easy and things you may want to do as part of a regular maintenance routine. By now, you may have found your issue. If not, please get help from an experienced professional before attempting to remove or replace intricate parts. Further, if you do not have the tools to perform some of the recommended tests, do not try to do so using makeshift methods. This can be dangerous and risk your safety. Always make sure your vehicle is turned off before working on it.