8 Reasons Why a Car Won't Start

Your car has been starting and driving flawlessly for weeks when one day you get in the driver’s seat, and your car sits there like a potted plant while you beg it to start, so you’re not late for work. But, no such luck.

Out of patience and desperate for answers, you go online to find article after article filled with the same vague information. This only tries your patience even more. We’ve all been there, and there’s never a convenient time for your car to break down.

#1 Reason Why a Car Won't Start

Car wont start due to bad weak battery


The most common problem that causes a no-start condition on cars is a dead or weak battery. Even if your lights, radio, and instrument cluster turns on, the battery may be too weak to start the engine. If you hear one or more clicks when you try to start the engine, you most likely have a weak battery, corroded terminals, or loose battery terminals. Even if you think the battery is good, double-check it. 

Jump-starting the dead battery will typically be all you need to do to get back on the road. If the car is stuck at home, you can use a 12 Volt Smart Battery Charger to recharge the battery. If the car is stuck in a parking lot, you can use a jump-box to start it. 

Thankfully for you, generally, a no-start condition is a relatively easy find and fix! The following table can help you narrow down the problem. 

Problem Symptoms Solution
Dead battery
  • None of the electrical components work (e.g., the lights, radio, etc.).
  • The battery light is on when starting the car.
  • No lights on the instrument cluster. 
  • You can't unlock the doors with the keyfob. 
  • car won't start, but lights are on
  • Charge and test battery. Replace if the battery does not hold a charge. 
Weak Battery
  • The doors unlock. 
  • Lights are dim. 
  • Dashboard and lights turn on. 
  • Car won't start just clicking.
  • The engine won't turn over.
  • The engine turns over very slow. 
  • You hear a click when you try to start the engine. 
  • car won't start in cold
  • car won't start after snow
  • The engine won't start, but the radio works
  • The engine won't start but turns over slowly
  • Jumpstart engine. 
  • Replace the battery if needed.
  • Check battery terminals for corrosion. 
  • Check battery terminals are on tight. They should not move.  
 Ignition switch
  • Car won't start
  • The Key may or may not turn in the ignition. 
  • Replace or repair the ignition switch. 
  • Temporary solution: Try turning the key on and off several times. 
  • Nothing happens when you try to start the engine. 
  • You may hear one or more clicks. 


  • Replace Start
  • Temporary solution: Tap on the starter with a rubber mallet to get the engine started a couple more times. 
Fuel Problem
  • Engine cranks but won't start.
  • Check engine light on
  • The car won't start but turns over.
  • Ensure vehicle has fuel.
  • Perform a fuel pressure test.
  • Replace fuel filter. 
  • Replace fuel pump. 
  • The engine won't turn over. 
  • The car won't start but may also turn over.
  • The car won't start, no noise.
  • Possible compression or timing chain issue. 
  • The engine may be hydro-locked or seized. 
  • If the engine turns over but won't start, it could be a bad head gasket. 
Electrical Issue
  • Symptoms can vary depending on the cause. 
  • The car won't start, no clicking.
  • Check engine light on
  • The Engine Control Unit may be faulty. 
  • The vehicle's anti-theft security system may be activated. 
  • Damaged wire harness. 
  • Faulty fuse or relay. 


For an engine to run, it needs three things: air, fuel, and spark. Therefore, I’m going to break this article down into the three categories you need for a car to start:

  • Air,
  • Fuel,
  • Spark.

Furthermore, we go over a few things that you can do to test, fix, and repair these conditions.

Before I get into the specifics of what does what and how to test it, it’s important to have an OBD-II engine scanner on hand. You don't need an expensive scanner. An OBD-II scanner that costs as little as $15 is able to read engine codes. Your local auto parts store may also read the codes for free.

engine car won't start

For more help, follow this guide to learn how to read check engine codes yourself.

This way, you can follow any codes that may arise due to your no-start condition.  This is the most vital step in the diagnostic process. The codes your read may not always solve the problem but can often cut your diagnostic time in half. More often than not, a code will take you straight to the problem area. All that is left is to complete the repair!


  • Clogged air filter
  • Bad PCV valve (positive crankcase ventilation)
  • Worn, chafed, cracked, broken vacuum lines.

Generally, it is rare for your car to not start due to not getting the correct amount of air. However, there are things you can do in your maintenance routine to prevent these conditions from happening.

1. Clogged Air Filter


Extremly dirty engine air filter blocking engine air flow

Most vehicle’s airboxes are easy to locate and easy to access. Consult your owner’s manual on recommended service intervals, but you should check your air filter at every oil change. Everything that you drive through or around has the opportunity to get into your car’s intake. That’s why when checking the air filter, you should be looking for dust, grime, and pollen buildup.

Another common thing to find within your air filter is bugs and other small critters. Especially if you live in a colder environment and have the potential to find small animals chewing and making nests within your air filter and air filter housing box, not only can this prevent the filter from doing its job, but you could also run the risk of your car’s intake being clogged.

The best way to see how plugged your air filter is is to remove it from the airbox and hold it up in front of a flashlight. Looking through the pleats, you should see a fair amount of light pass through. If you do not see the light in a majority of the filter, or the light passing through is minimal, the filter should be changed for best engine performance and fuel efficiency.

2. Bad PCV Valve

Blocked PCV valveThe PCV valve (positive crankcase ventilator) is probably the most overlooked yet simple maintenance item.

A PCV valve (if your car has one) is a plastic and rubber “breather” located along or near the intake manifold.  If your car does not have a PCV valve, it will have a restrictor or vacuum hose completing the same function. Either way, all of these components can fail and need to be inspected.

The purpose of the PCV valve is to return blowby gases pulled from the crankcase. This improves fuel mileage and makes for a “cleaner,” more eco-friendly burn emitted back into the atmosphere.

For the sake of this article, I will focus on a PCV valve being stuck open. This is the most common failure that would result in a no-start condition.

More specifically, symptoms include:

  • Engine misfire
  • Rough idle
  • Increased oil consumption
  • Presence of oil within PCV valve or vacuum line
  • Rough or no-start

Testing the PCV valve is easy and inexpensive to replace if you find yours is the cause of your no-start condition.

  • Locate the PCV valve and inspect it for obvious hydrocarbon, oil, or grime build-up. As well as all other vacuum lines connected to or around the PCV valve.
  • Let your vehicle get to operating temperature, then unplug the PCV valve. Place your finger on the end of the PCV valve and feel for vacuum. If you do not feel a vacuum, there is most likely an obstruction in the breather screen within the PCV valve or the vacuum line.
  • If your PCV valve is operating normally, you will notice when you place your finger over the PCV valve that your engine would drop between 40 and 80 RPMs. Then climb back to normal idle. This dip in RPMS is momentary.
  • If you notice that your RPMs drop more severely, then your engine seems to smooth out, your PCV valve may be stuck open.

If you find an obstruction in the vacuum line or PCV valve, you can clean this out with carb cleaner or solvent and use a soft bore cleaning brush to free the obstruction. However, if the obstruction is within the PCV valve, it is best practice to replace it.

3. Worn, Chaffed, or Broken Vacuum lines

check vacuum lines

If you find that your car still isn’t starting or starting roughly after testing your PCV valve, then further inspection of the surrounding vacuum lines is a quick way to eliminate whether or not you have an “air” problem with your car.

The best way is to look for obvious signs of chaffing and cracking. Check along areas where hoses may come in contact with the engine block or engine accessories. The vibration of the engine and driving down the road will quickly cause premature wear resulting in pinholes in your vacuum lines.

Starting the engine and allowing it to idle. Spray carb cleaner such as Seafoam near and around the vacuum lines and intake. If you spray near the cracked hose, the engine will react to the spray by increasing the engine idle speed as the cleaner is burned.

Another big factor potentially damaging your vacuum lines is the heat from your engine or other environmental factors causing the rubber and or plastic lines to dry rot, causing a leak resulting in loss of vacuum suction.

If you notice that a worn or cracked vacuum line is the culprit for your no-start condition, electrical tape around the hole or crack is a fast fix to get you back on the road until a replacement can be found.


  • Bad fuel
  • Loss of fuel pressure or prime
  • Clogged fuel filter or injector(s)

The first condition listed, bad fuel, is a rare reason why your car would be having a no-start issue. However, this is often overlooked. Especially in colder climates, too much water in the tank can cause a no-start. Not having the correct air, fuel, and spark mixture will not allow for proper compression within the cylinders.

A few measures you can take are:

  1. Make sure you put the correct fuel in the tank.
  2. If you live in a cold climate, make sure your tank never gets below ½ tank.
  3. If you know it will be especially cold (in the negatives), treat your fuel tank with a bottle of Heet fuel treatment. This is sold at auto parts stores and most gas stations, and even Box stores.
  4. If you have a vehicle that isn’t driven very often, make sure that if you live in a climate where the seasons drastically change, you fill the tank before winter in the late fall. Gas stations switch their “summer fuel” with their “winter fuel” in the winter mix; there are often additives to help eliminate moisture.

If you suspect that there is water in your fuel tank, adding Heet to your tank after the fact will eliminate the water within your tank and will get you started. Make sure you fuel at the nearest fuel station ASAP.

4. Loss of Fuel Pressure or Prime

Loss of fuel pressure or prime is probably one of the most common no-start scenarios.

Often there are warning signs your fuel pump is getting weak before your car doesn’t start.

 In the days leading up to a no-start condition, your car may:

  1. Crank more than usual to get your engine running.
  2. Your car may also sputter or die under a load (driving up a hill or during acceleration)
  3. Decreased fuel efficiency

Checking your fuel pump at home is rather easy, and there are virtually no tools required.

The easiest way to check the functionality of your fuel pump is to get in your car, shut the door, and turn the accessory on. At this time, you should hear a humming sound. This is the electric priming of your fuel pump. This puts the correct starting fuel pressure at the fuel rail on the engine.

If you do not hear a humming sound, the next thing would be to open the hood and locate the fuel rail. On the fuel rail, oftentimes, there is a Schrader valve used to connect fuel pressure gauges.

test fuel pressure if car won't start

At this Schrader, you can again turn on your accessory and then walk to the engine bay and use a pocket screwdriver or pick to push the Schrader valve down and see if there is fuel at the fuel rail. You can use a fuel pressure test gauge to check the fuel pressure at this valve. 


No fuel pressure engien won't start

Lastly, if you don’t hear a humming with your accessory on and/or you don’t have fuel at the Schrader valve on the fuel rail, check your fuel pump fuse. Fuses are the easiest first-step diagnostic tests. Typically fuse panels are under the hood. There is typically a fuse box cover, and under the lid is a fuse legend you can follow to help determine what fuse is where and what amps they are. If this is not present on your fuse box cover, oftentimes, there is a legend in your operator's manual.

5. Clogged Fuel Filter or Injector

As cars get newer, more and more often, the fuel filters are left “unserviceable” and are integrated within the fuel tank and are one module with the fuel pump. In this case, if you had a bad fuel pump, the filter and pump would be replaced at once, and you do not have to worry about separate fuel filter maintenance.

Typically, if your fuel filter is serviceable, it is in line with the fuel lines. To find your fuel filter, locate the fuel tank underneath the car and follow the lines (that are normally fastened to the car's frame) all the way to the engine. About halfway between the engine and the fuel tank, there is a cylinder-like component. This is your fuel filter. You can’t always tell if your filter is clogged just by looking at it. But typically, if your filter is clogged, it will show signs of leaking and have a lot of surface rust on it.  These filters are relatively inexpensive and easy to replace yourself.

If you do not have an in-line fuel filter, you may have a cartridge or spin-on filter that can be found within the engine bay. Usually, once you take these off, you should replace them with new ones. So if you suspect that your fuel filter is at fault, it’s probably not a bad idea to replace it.

There are ways to test if the filter is bad by bypassing the filter in its entirety. However, this procedure is normally more work than it is worth and can take some time to put together a bypass line. But if you have the time and want the experience, I say, DO IT!


If you have tested your fuel system up to this point and everything still seems to be checking out, the last step is to check your fuel injectors.

The best and easiest way to test a fuel injector is to unplug each injector from the wiring harness and use your voltmeter on the ohm setting.


If you are experiencing a no-start condition, though, you want to look for the injector or injectors with an ohm reading that is off significantly from the others.

If you find you have a clogged fuel injector, you can clean it by removing the fuel injector from the engine and using a solvent and fuel injector tip cleaners to remove hydrocarbons. If your car starts after this procedure, you can buy a fuel injector cleaner and add it to your fuel tank. This additive is designed to help minimize and clear out hydrocarbon build-up.  When you test your fuel injector and find that the ohm reading is off from the manufactures spec, and the fuel injector does not seem dirty or clogged, your injector is probably a “dead” injector that cannot be repaired. At this time, this injector or injectors would have to be replaced.


No spark no start

This section is usually the culprit of most no-start conditions. In this section, I will go over:

  • Batteries and Battery Cables
  • Starter solenoids
  • Spark Plugs, Sparkplug Wires, Sparkplug Coils

6. Batteries and Battery Cables

The battery should always be the first place you go when you find yourself in a no-start circumstance. If your vehicle battery does not have enough Cranking Amps to turn your engine over, you may have a dead battery or a bad cell within the battery. Most batteries are non-serviceable, and if you have a bad cell, generally, you would replace the battery.

But, if you find that you left your lights on too long or your accessory on and your battery is just drained, you can jump your car with the use of jumper cables, another car, or a jump pack. If your car starts with a jump, then you’d want to let your car run between 10 minutes to half an hour to properly let your alternator recharge your battery. After your car has run and you feel your battery is properly charged, shut your engine down and try to restart. If your car starts up like normal, you are most likely in the clear.

However, it is good practice to have a car battery charger on hand to let your battery “trickle charge” for a few hours or even overnight to prevent premature battery failure.

If you get, your car started and know the battery is in good standing but still have issues with your battery “draining,” your car may be experiencing parasitic draw. This can come from any electrical component in your vehicle. However, for this article, bad battery cables could be the culprit of your battery’s draw.

A battery cable goes “bad” when there is too much resistance in the cables, and the energy from the battery is absorbed into the cables. High resistance in battery cables typically comes from corrosion from moisture or kinks or chaffing within the line itself.

This test is easy to do with a voltmeter. Connect your positive meter lead to the positive cable at the battery


Then connect the negative test lead from your meter to the other side at the positive battery cable to the starter. Again, you want the cable contact, not the pos—starter post. Crank the engine, then watch your voltmeter. Your voltage drop should be no more than .25 volts. Before cranking, your meter should read 0v. When you start cranking, if your meter reads more than .25 volts, there is an excessive voltage drop in that cable, and you would need to replace the positive cable. The same goes for the negative battery cable. For this test, you want to place one lead of the voltmeter onto one end of the battery cable at the starter and then the other lead on the negative battery post. Once again, crank your engine and make sure your reading is as close to 0v as possible. Generally, more than .25v is out of spec.

7. Starter Solenoid

If you find your engine does not crank at all, you may have to see if your starter is even operating. When you go to start your car, listen for a click. If you have a click, that generally means that the starter is getting the correct voltage from the battery, but the starter motor is faulty. If you’re unsure if you hear the click you need to hear, you can also confirm whether or not you’re getting voltage by placing your voltmeter on the s terminal on your starter solenoid and the ground starter (generally grounded through the starter itself. So the starter body would be an acceptable place to put the test lead.

Then have someone turn the key for you as if they were to start the vehicle and read if you’re getting battery voltage. If not, then you would have a problem somewhere in the starter signal circuit. If you are getting battery voltage, then a new starter is probably required for your car to start.

8. Sparkplugs, Sparkplug Wires, Sparkplug Coils

bad spark plugs

There are many sparkplug testing tools out there. But the easiest way to accomplish this test at home is to remove them from the sparkplug hole and physically inspect them. You want to make sure your electrode is not worn away and have the correct spark plug gap. The spark plug gap is measured with a specific spark plug gap tool that measures the space between the electrode and the metal end just above the electrode, causing the electrical ark.

Spark plug wires should be replaced whenever the spark plugs are replaced. Sparkplug wires can chafe and crack just like any other hose-like component in the engine bay. If your sparkplug wires chafe together and arc amongst one another, the required voltage to the sparkplugs is not reached.

Lastly, when it comes to the spark plug coils, generally, this will not be why your engine does not start. Typically this will cause an engine misfire, decreased fuel economy, and other similar symptoms to faulty sparkplugs. Thankfully, testing a spark plug coil on your own is fairly easy. There are tools on the market as well as ohmmeter readings you can take on the coil itself. But, when you have a suspected bad coil, the best thing to do is switch it with another coil from a different cylinder. For example, if you have a misfire on cylinder one, you can switch the coil from cylinder one to cylinder four. If the misfire “follows” and goes to cylinder four and now not on cylinder one, then you can conclude that the coil for cylinder one is responsible for your engine misfire.

In conclusion, there seems like there is a lot that causes your car not to start. Hopefully, from this article, you have a lot of your questions answered and further knowledge on what to do if you find yourself in a no-start condition. As you can see, the tests are fairly easy to diagnose and repair all on your own, helping you better understand your car and how it runs and functions.

Once you start the car, you may notice that the check engine light is on. Follow this guide to learn how to troubleshoot the check engine light.


Frequently Asked Question

Why won't my car start when I try to jump-start it?

  • Make sure that the jumper cables are making good contact. In some cases, the battery may be completely dead and requires to charge for 15 minutes before you can start the engine. If using a jump box, make sure it is fully charged. 

Why won't a car start after a jump start?

  • It is possible that you connected the jumper cables backward. If that is the case, you may have blown a fuse. It is also possible that the main battery is completely dead and needs to be replaced. 

Why won't a car start after sitting for a long time? 

  • The problem most likely is a weak or dead battery. If the car has been sitting for months, then you are more likely to have a fuel-related issue. 

Why won't my car after the new battery was installed?

  • Make sure that the battery cables are not connected backward. Red cable goes on positive (+) post. Also, make sure both clamps on the terminal post are on tight. We have seen many cases where an owner installed a new battery but didn't fully tighten the battery terminals. 

The car won't start and the brake pedal hard; why? 

  • It is normal for the brake pedal to be hard when the engine hasn't started. Once the engine starts, the brake pedal returns to normal operation as vacuum from the engine makes it easy to apply the brakes.