Why is My Engine is Not Starting?

Is your engine not starting or cranking over? You have come to the right place. We are a team of ASE certified mechanics who have created this guide for you. The instructions below will help show you the easy things to look for first and then progress to the harder to diagnose problems. Let's get started!

If the car stalls while driving and then starts back up immediately, it can be more difficult to diagnose: Engine stalls while driving

If the engine is hard starting while 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 with a spark at the plug at the correct time. Check out the video below to get an idea on what needs to happen inside in each of the cylinders for the engine to run.

Quick video overview on what to look for when the engine will not run. When done watching please travel down the guide to gain valuable additional information on the problem.

We have created this guide to help you fix your car and for you to better understand what could be wrong weather you are fixing it yourself or taking it into a garage. The problems below are listed in order of popularity and apply to gasoline and diesel burning engines, so let's get started!

Step 1: Check the Security System

A security system is built into most vehicles which disables the ignition or fuel system when activated. Occasionally the system will simply become confused due to a glitch or a procedural error. If the security light is flashing when trying to start the car the system has been activated.

Exit the vehicle and lock all of the doors with the windows up, then wait two minutes, next unlock the vehicle by the drivers door lock this should reset the system, try to start the engine. If the light is still flashing try the spare key, if the light goes out it is because the frequency chip located inside the first key could have gone bad. This could be due to age in which case you will need a new key from the dealership. If the light is not flashing continue down the guide.

Step 2: Test Vital System Fuses

A blown fuse will make the engine not start. 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

Step 3: Read The Engine Trouble Codes

When 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 codesA 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 does not cost much for a code reader. If you do not have a code reader you can easily purchase one online from places like Amazon. Plug the 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

Step 4: 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 forty five minutes give or take depending on location and the accessories that maybe needed to be removed to perform the repair.

crankshaft angle sensor repair

Step 5: 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 quiet 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 seems 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

Step 6: 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 five 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

Step 7: Check the Cylinder Compression

For an engine to work three things are needed to happen inside of the 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

Starter is Not Cranking Over

You go out to your car you turn the key and the engine is not cranking over. This is when you can lift the hood and do some checking to see if it is something simple or a little more difficult. When the engine is not turning over it can be mainly due to three separate areas of the car, first the area could be the battery, next is the starter or its trigger circuit and finally a problem with the engine or one of its accessories.

Some of these things are easy to fix while others can be a little tougher which I will describe in this repair guide. We will go over each one of these issues in order of popularity to show you the first things to check and get you back on the road, let's get started.

Step 1: Test for a Dead or Weak Battery

A battery is a chemical based voltage storage unit that loses it ability to hold a charge and delivery the amperage needed to operate the electrical system and more importantly the starter motor. Through time, most likely between three and four years, this chemical reaction will begin to break down rendering the battery useless. One thing you need to know is the starter pulls a high amount of electrical amperage from the battery to operate. Avoid trying to crank the engine over when anyone is near the battery. A battery is sometimes filled with explosive gasses that can ignite when extreme heat or a spark is present. When turning the ignition key to the crank position you may notice a few different scenarios which can mean the same problem:

  • You turn the key to the on position and the dash lights go out or are dim
  • You turn the key to crank the starter and it goes for a brief time, but then it stops and you hear a loud clicking noise
  • The engine turns over slowly and then stops.
Residual battery acid around the top of the battery can be present so wear gloves and avoid touching your clothes or skin when working on or near the battery. If needed use baking soda and a garden hose to neutralize any acid residue before you begin the repair or testing. If in the dash the battery warning light has been on prior to this repair then the battery will need to be jumped to get the engine running and regain its charge. Jump the battery using jumper cables which you can purchase online from sites like Amazon. Be careful not to connect the jumper cables backwards by connecting the negative to the positive battery terminal or you can cause electrical system damage, once the engine is running test the alternator voltage output.

Learn More: Testing an alternator

If the battery warning light is not on while driving this means the system is probably being charged properly and the battery has lost its ability to hold a proper charge. Load test the battery to confirm its condition which can be done using and observing the headlights of the car.

Learn more: Load testing the battery

If the battery fails its load test it will need to be replaced with a new or good used battery of comparable size and cranking amps. This can be done easily using everyday tools while wearing protective gloves to protect against residual acid which can be present on a bad battery. You can get an Optima or AC Delco replacement battery which last longer but cost a little more online from sites like Amazon which you can get through prime in one day, or just head on down to your local parts store for a replacement. Record radio preset stations for re-entry before removing the battery.

Learn more: Battery replacement

Step 2: Check the Battery Cable and Connections

The battery supplies voltage to the starter through two battery cables, positive and negative, which need to be clean and tight while being free from corrosion. If you know the battery is good because it is fairly new or you tested it and it passed, you could have a battery connections problem at the terminals or starter motor itself, here are the symptoms of a bad connection.

  • While the dash lights are bright you turn the key to engage the starter and the dash lights go out and nothing happens
  • The starter begins to work, but then it suddenly stops and the dash lights go out and nothing happens.
The battery cables are used to transfer the battery voltage to the engine starter and to the electrical system, these cables are subject to battery acid which can produce an internal cable failure. When this condition occurs the car will act much like a dead battery by not allowing the voltage to continue to the starter motor. Check both the negative and positive battery cables for abnormal bulging, weakness or corrosion. This problem can be sometimes overlooked by most mechanics and can be intermitted.

Corrosion and loose connections is the enemy of electrical current flow. These conditions cause heat which will produce the power disconnect, this is why this problem will come and go, because when the connection cools it can start working again. Inspect the battery cable ends for corrosion which means they need to be cleaned, also while wearing rubber or vinyl disposable gloves grasp both negative and positive battery cable ends and try to wiggle them to check for tightness.

Then use a wrench or socket to loosen and remove the cable end. Be careful not to touch the wrench or ratchet to any metal parts or the opposing terminal to avoid a short circuit. If the end is badly eaten away by acid you may need to use a pair of channel locks to work the cable end loose. Then replace the battery cable end which you can get from Amazon or the local parts store. 

Once the battery cable end has been removed use a terminal cleaner or a wire brush to remove all corrosion or rust on the cable end and battery terminal. This is done by inserting the cleaner tool into the cable end and twisting it back and forth. This tool has a tapper fit which you should observe because it will only work in one direction on the cable end. After the terminal and cable end has been cleaned thoroughly reinstall and tighten. Push down on the cable end while tightening will help secure the connection.

Once the repair is complete, try to wiggle the cable end it should be nice a tight which means the repair is done correctly, reinstall the terminal cover.

Learn more: Battery cable end cleaning

With the Lights Bright you Engage the Starter Motor and Nothing Happens

In the following cases you try to use the starter and nothing happens the engine makes no noise at all.

Step 1: Move the Gear Shifter to Neutral or Fully Depress the Clutch Pedal

Vehicles equipped with automatic transmission are designed with a neutral safety switch that will not allow the engine to crank over if the gear selector is not in park or neutral. For standard transmissions the switch is designed to detect if the clutch pedal is fully disengaged. This safety feature will not allow the engine to start while in gear which will have the car take off unexpectedly when the engine starts.

Both of these switches are subject to wear and can become mis-adjusted or have an open circuit due to time and usage. Furthermore if the clutch pedal is not fully depressed due to a floor mat that has become logged under the pedal or the gear shifter on the automatic transmission is loose or broken the starter will not operate.

Check to see if the floor mat has become lodged under the clutch pedal and reposition it out of the way to allow full travel of the pedal. For automatic transmission cars move the gear shifter to the neutral position and recheck the operation. If the starter works the switch has gone bad and needs testing, adjustment or replacement.

Learn more: Testing a Neutral Safety Switch

Step 2: Check the Starter Fuse and Relay

Like most heavy electrical load components such as starter there is a fuse and relay to protect and control the system via the ignition switch. These components are usually located in the fuse panel or power distribution center under the hood. If an electrical surge occurs or if the fuse ages it can fail causing the starter to not operate. Likewise if the starter relay that follows the fuse stops functioning because of an internal short circuit or the contacts fail due to usage there will be no trigger voltage supplied to the starter solenoid.

Using a grounded test light locate the fuse panel and test the system fuses, replace any that have failed and recheck the starter operation. If the fuse tests okay continue down the guide.

Learn more: Testing the starter fuse

The starter relay is next in the circuit to supply power to the starter solenoid which engages the starter motor operation. Some vehicles are not designed with this relay in which case you can skip this step. To be sure if your car is equipped with one of these relays check your owners manual or the fuse panel identification information located on the lid of the panel.

When this relay fails it can do so in two different ways, first the relay may make a ticking noise like it is working, but the contacts inside the relay are burnt not allowing the power feed of the relay to be transferred through to the starter solenoid. Next the electric coil winding will fail causing an open circuit not allowing the relay to work (no ticking noise). In either case the relay must be tested and then replaced if found to be bad.

To test this relay a small jumper wire and a test light is needed. Remove the relay and check for power at two of the terminals in the power distribution center. If power exits the relay is probably bad, but to be sure more in-depth testing is needed.

Learn more: How to test an electrical relay

Step 3: Test the Starter Motor Trigger Wire

Before the starter motor can work the solenoid that is responsible for its operation must receive a voltage signal. This signal, is the final destination for the voltage which originates from the operation of the ignition switch by the driver. If everything before this point tests or looks okay you will need to test the starter motor trigger wire for power while the key is in the crank position to determine the condition of the starter.

In some cases it will require you to get under the car and located the starter motor which is usually on the right or left side near the rear of the engine block and sometimes under the intake manifold like on Nissan and Infiniti V8 engines. Lift your car safely using a hydraulic floor jack and secure the vehicle with jack stands to access the wire for testing.

Once the vehicle is lifted locate the starter solenoid trigger wire which is the smaller of the two electrical connections. Attach a test light to ground and have a helper hold the key to the crank position. Hold the point of the test light on the terminal of the trigger wire on the solenoid, the test light should light up, also test the large power terminal which is connected to the positive side of the battery it to should also have power.

Do not connect the test light probe to ground while checking for power to avoid a short circuit. If both terminals have power the starter has failed and replacement is required. Sometimes you will here the starter click but not activate, this is telling you the solenoid is working but the motor part is bad in either case the starter motor has failed and needs replacement.

Learn more: Replacing a starter motor

Engine Noises - Troubleshooting Starter and Flywheel for Mechanical Failures

Many abnormal noises can occur while the engine is not cranking over. These noises include grinding, whirring or a loud clunk indicate and mechanical failure of some kind, we will go over these sounds and the repairs needed to get you back on the road.

The starter is a high torque electric motor fitted with a small gear and a mechanism called a bendix. This small gear engages with the large gear called a ring gear on the flywheel if the car has a manual transmission, and onto a flex plate with cars fitted with an automatic transmission. The small gear contacts the large gear only when the starter is engaged and then retracts after the engine starts and the ignition switch is let up to the run position.

The solenoid is a electro magnetic switch and lever that throws the small gear outward into the flywheel while turning the starter motor on. If the solenoid fails it will not push the bendix gear into the flywheel completely which then creates a grinding noise. When this small gear wears or the bendix failed is will cause a grinding or whirring sound which means the bendix is not working and the starter must be replaced.

Once the starter has been removed check the flex plate or flywheel condition. This means observing the teeth of the ring gear which contacts the pinion gear of the starter. If teeth are missing or badly worn the unit must be replaced before installing the new starter. Below is a picture of the flywheel on the rear of the engine with the transmission removed.

Learn more: Flywheel replacement

Step1: Engine Mechanical Breakdown

If the starter makes a single clunk noise and then nothing it might be working fine. The problem could be the engine is not allowing it to work because it cannot be turned over due to a mechanical failure of some kind. To start troubleshooting remove the serpentine belt and check to see if each of the accessories such as the water pump, alternator, air conditioner compressor and power steering pump spin freely and are not locked up not allowing the engine to turn via the belt.

Lean more: Remove the serpentine belt

With the belt removed check for internal mechanical failures which can stop the engine from rotating such as a spun rod or crankshaft bearing, broken piston or rod, dropped intake or exhaust valve or a blown head gasket. The easiest way to do this is to see if you can manually turn the engine over by hand. Check for this problem by installing a large wrench or socket with a long handle fitted onto the front crankshaft bolt and try to move the engine clockwise, it should be difficult, but not impossible to turn. If the engine is locked up it will need to be replaced or repaired.

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 would not 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. This is where our online mechanics hang out and will give you the answers you need.

Article first published