First Things To Check When Your Car Will Not Start

It can be frustrating when your car won't start. Most car owners will experience a engine starting issue at least once in their driving lifetime.

This guide has easy to follow instructions, which applies to vehicles with gasoline burning engines.

If your car is not cranking over then you have a different problem and you need to follow this guide instead: What to do when your engine is not cranking over

If it seems like the car is hard starting because its taking an abnormal amount of time to catch and run then you need to follow this guide: How to repair a hard starting engine

What makes an engine run?

For an engine to run it must have compression, the proper amount of fuel and air mixture with a spark at the plug at the correct time. Check out the video below to get an idea of what needs to happen inside in each of the cylinders for the engine to run.

Test Vital System Fuses

Fuses are used to protect various electrical circuits while supplying power to components such as the fuel pump, injection and computer systems from suffering a short circuit and possibly causing an electrical fire. When these fuses blow the system they support stops working and the engine stops running. 

When a fuse blows it does so for one of three reasons.

  • There is an electrical surge in charging system or the battery has been jumped backwards
  • The fuse ages and pops
  • A short circuit exists because a wire, sensor, amplifier or computer has shorted to ground
Learn more: How to check electrical fuses There are two methods of checking electrical fuses that protect various components, you can either pull each fuse out and inspect it by hand or use a test light and check its continuity. If a blown fuse is found check the system it belongs to by using the vehicles owner's manual or the identification chart on the fuse panel cover. Once the system is identified remove and inspect or replace the failed part and retry the engine. If the fuse still blows you will need to check the wiring harness for damage or a broken wire and repair it.

how to check fuses

Check For A Crankshaft Angle Sensor Failure (P0335)

The crankshaft angle sensor is responsible for sending feedback data to the main computer which in turn translates it into usable information which controls the injector pulse and ignition timing. When this sensor fails the computer see's the engine as not turning which in turn will not send pulse signals to either fuel or ignition systems. This problem causes the engine to crank over but not run.

This sensor is subject to heat and engine vibrations and is inexpensively produced in mass qualities creating high failure rates. When this sensor becomes worn or weak it will fail to produce the alternating currant needed for the computer to read.

Learn More: How to replace a crankshaft angle sensor These sensors are located either at the front, middle or rear of the engine near the bottom of the block where the crankshaft resides. Replacement takes about 45 minutes give for take depending on location and the accessories that maybe needed to be removed to perform the repair.

crankshaft angle sensor repair

Test the Fuel Delivery System

The fuel system is used to deliver the proper amount of fuel at the correct time of the cylinder's compression cycle. This is performed by the fuel injection system which consists of a fuel injector for each cylinder, a fuel pump which is located in the fuel tank and fuel lines that travel from the tank and head up to the engine and into the fuel rail where the fuel injectors reside. This entire system is controlled by the computer; if there is a malfunction the electronic injector drivers inside the computer will not send a trigger signal to allow fuel to enter the engine.

If fuel is not entering the cylinder's combustion chamber the engine will not run and deliver the individual cylinder power as intended. This could be due to a fuel pump that has failed and is not supplying fuel pressure, or the injectors themselves are not operating correctly allowing the proper amount of fuel to be distributed into each cylinder for the piston to ignite.

A fuel pump is a basic electrical motor that is subject to vibration and can fail due to wear and usage. These pumps are cheaply mass produced which increases the risk of them not working. A fuel injector is simple magnetic on and off valve that is controlled by an electrical pulse supplied by the main computer. These units are subject to heat, engine vibration and fuel impurities such as gunk and dirt that can make them clog. If one of them short circuits it can cause the injector driver to "lock up" not allowing any of the injectors or fuel pump to operate.

Learn more: How to test a fuel pump The easiest way to check if the fuel pump is turning on is to be very quite and switch the ignition key to the on position without cranking the starter. You should be able to hear the pump running in the rear of the car. If you are unsure of its operation then you will need to test the fuel pressure. If no pressure is present then confirm the fuel pump being bad by using a wring diagram for your vehicle and probing the pump power wire using a test light.

fuel pump power test

If the fuel pump electrical system and pressure seem to be working okay the next step is to test the injector pulse. This can be done by using a test light while the engine is cranking over to see if the injector is getting a trigger signal from the computer.

Learn more: How to test a fuel injector testing fuel injector pulse

Test The Ignition System

The ignition system is designed to ignite the fuel air mixture inside the combustion chamber via the spark plugs. This is done by using an ignition coil, a crankshaft and camshaft angle sensor along with the car's computer or PCM (Power Control Module). This system can stop working due to a failed ignition module or the crankshaft angle sensor which is very common.

Ignition components are subject to heat and the vibration of the engine along with the constant wear of building an electronic field and then releasing it to amplify the voltage needed (25,000 to 35,000 volts) to bridge the spark plug gap which ignites the fuel. When spark plugs wear they cause this voltage to build higher then the coils and the ignition system is designed for which creates a failure by overheating.

Learn More: How to Test the ignition Testing the ignition system is an easy job that takes about 5 minutes and can be done using a test light or an extra spark plug. Connect a test light to ground and with one of the spark plug wires or coils disconnected. Crank the engine over while holding the tip of the test light about 1/4 (7mm) inch from the wire or coil terminal. Keep your hands clear of the test area to avoid an accidental shock. You can also insert a spark plug into the coil or wire and hold it against a metal ground. You should see a light blue spark in the gap, this is telling you the system is working. If no spark is present more testing of the system will need to be done.

testing the ignition ssytem

Check the Cylinder Compression

For an engine to work three things are needed to happen inside it's cylinders to crank over and run; compression, fuel and ignition. Cylinder compression is the result of the proper correlation of the crankshaft, camshaft and valve system while the pistons travel upward in the cylinder bore. When the volume of compression drops below about 85 psi combustion is not possible.

Cylinder pressure can be affected by a mis-alignment of the crankshaft and camshaft that can put the valve timing out of sync with the pistons. The most common cause for this is a jumped timing belt or timing chain. Improper maintenance such as not changing the oil and filter can cause premature wear of chain where as the belt is a regular service item that should be replaced between 70,000 and 90,000 miles.

Learn More: Testing Engine Compression Checking engine compression is not too difficult and can be done with a spark plug socket and a compression gauge. Remove the ignition or fuel pump fuse and one of the easiest spark plugs to perform the test. If compression readings are between 125 and 170 psi the compression is normal. Most of the time if one cylinder has the correct compression the engine will start and run, if one or more cylinders have low compression the engine will misfire and have a rough idle but still run. When the compression is low or non-existent the engine will crank over freely with little resistance to the starter a sure sign the chain or belt is a problem.

checking engine compression

Read The Engine Trouble Codes

When a vital sensors or controllers fail in the engine computer system such as a crankshaft angle sensor, ignition amplifier or fuel pump controller it will stop the engine from starting. This is because the engine needs spark at the time of compression and fuel to enter the combustion chamber to run.

A computer sensor, electronic controller or amplifier is exposed to heat and vibration which can cause the internal workings of the unit to stop operating. These failures include an open or short circuit in the electrical part of the sensor making it non-operative.

Learn More: How to read trouble codes A check engine, service engine soon or MIL is telling you there is a diagnostic trouble code stored in the car's computer. These codes are designed to give you an idea of the system or sensor that is causing the engine not to start. When these codes are present it means the computer has detected a failure which when corrected can fix the trouble. Today's cars are easier than ever to read the codes and it doesn't cost much for a code reader if you don't have one from places like Amazon. Plug a code reader tool or scanner into the ALDL port which is located on the driver's side near the bottom of the dash in most cases and gather any codes that are present.

how to read engine computer trouble codes

More Obscure Starting Issues

There a few subsequent conditions which are more difficult to detect which will cause your engine not the start and run such as:

  • Water in the fuel tank
  • Electrical system wiring harness failure
  • Computer malfunction
  • Car was driven through a deep water puddle causing electrical components to get wet.
Before your car wouldn't start did you notice anything out of the ordinary while it was still running such as low power or the check engine light on? This could aid in the troubleshooting and diagnosis of the problem. If you are taking your car in for repairs, be sure to mention anything you noticed before the trouble began to your mechanic.

Got Any Questions?

Check out our engine not starting forum if you have questions. Our community would love to help you. Most of us are mechanics by trade and will answer any question you might have.

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