How to Fix an Engine Not Running

Engine not running or cranking over can be an easy fix

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 these instructions which will help check the easy things first and then progress onto the more difficult problems. We have included the two different problem scenarios; the engine is not running and the engine is not cranking over. The first section is for an engine that won't run. The second section is for an engine not turning over.

What Goes Wrong?

An engine needs three things to run; Compression, fuel and spark. Because the engine depends on supporting systems to make these things happen such as the fuel and ignition systems a simple item such as a fuel pump relay will make the engine not run. When the engine is not cranking over a simple item such as a low battery can fix the problem.

How much does it cost?

Troubleshooting an engine that does not run and does not crank over will be different. If the engine is not cranking over and you have towed it to a repair shop to troubleshoot the problem it should cost between $30.00 if it's an easy and $140.00 if it a more complicated electrical issue. If the engine is not starting then more diagnostic time maybe needed. Again, there are simple and complicated problems for both of these scenarios.

Let's Get Started

This section is for an engine that cranks over but will not fire up.

1. Check the Security System

A security system is built into most vehicles which disable 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 and then wait 20 minutes. Then unlock the vehicle by the driver's door lock or remote this should reset the alarm system and then try to start the engine. If the light is still flashing try the spare key. If the light then goes out it is because the frequency chip located inside the first key has 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 with our guide.

2. Test Fuses

Fuses are used to protect various electrical circuits while supplying power to components such as the fuel pump, fuel 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. 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 to 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. If all fuses are good continue with our guide.

Fuse Test Video

3. Check for Spark

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, 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 crankshaft angle sensor, or fouled or worn spark plugs which is very common. 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 inch (7mm) from the wire or coil terminal. Keep your hands clear of the test area to avoid accidental shock (non lethal). 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 suspect the crankshaft sensor will need replacing which is the most common problem.

Test Ignition System Video

4. Check for Fuel

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 is located in the fuel tank with fuel lines that travel from the tank and up to the engine and into the fuel rail where the fuel injectors reside. Common fuel system problems are due to a fuel pump that has failed and is not supplying fuel pressure. Or the injectors are not operating correctly allowing the proper amount of fuel to be distributed into each cylinder for the piston to ignite. 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 and needing replacement by using a wring diagram for your vehicle and probing the pump power wire using a test light.

Fuel Pressure Test Video

Fuel Pump Replacement Video

5. Check Engine Trouble Codes

When a sensor or a controller fails in the engine computer system such as a crankshaft angle sensor, ignition amplifier or fuel pump controller it will stop the engine from starting. 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 problem. 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 for about $40.00 (US). 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. The video below shows a Honda Civic being done but it is the same for most cars.

Check Engine Codes

6. Crankshaft Angle Sensor

A bad crankshaft angle sensor may not show up on a code scan as being faulty. When this sensor fails the computer see's the engine as not turning which may not be the fault of the sensor as far as the computer is concerned such as a bad starter. 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 of the crank sensor takes about fortyfive minutes give or take depending on location and the accessories that maybe needed to be removed to perform the repair.

Crankshaft Angle Sensor Replacement Video

7. Check for Injector Pulse

Injector pulse is needed for the fuel to enter the engine through the injectors. This test will let you know if the computer is working by triggering the injectors for the engine to run. If there is no trigger then the computer is not powered up from the ECM relay or some other electrical issue is involved. Checking injector pulse can be done by using a test light while the engine is cranking. This will test if the injectors are getting a trigger signal from the computer.

testing fuel injector pulse

8. Check Cylinder Compression

The engine requires compression to ignite the fuel to make the engine run. Cylinder compression is the result of the proper correlation of the crankshaft and camshaft 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 misalignment 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. Checking engine compression is not too difficult and can be done with a spark plug socket and a compression gauge which you can rent for free from your local parts store. 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 the problem.

Engine Compression Test Video

9. Plugged Exhaust System

Engine exhaust must be able to be relieved from the engine to allow it to run. If there is an obstruction such as a catalytic converter that has broken and plugged the exhaust system no exhaust gasses will be able to exit the engine. In this case remove the exhaust head pipe to allow make sure the exhaust system is not a problem.

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.

Watch the Video!

What to look for when the engine will not run. This video shows how a mechanic would tackle this problem.

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 such as low power or a check engine light? This could aid in the troubleshooting and diagnosis process. If you are taking your car in for repairs mention anything you noticed before the trouble began to your mechanic.

If the car stalls while driving and then starts back up immediately that is a slightly different issue that will be able to fixed by visiting: 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: Hard starting engine.

Section 2: Starter is not working

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 we will describe in the following repair guide. We will go over each one of these issues in order of popularity to show you the first things to check so we can get you back on the road.

1. Test the Battery

A battery is a chemical based voltage storage unit that loses its ability to hold a charge and delivery the amperage needed to operate the electrical system and more importantly the starter motor. Between three and four years the chemical reaction inside the battery will begin to break down and weaken it. One thing you need to know is the starter pulls a high amount of electrical amperage from the battery to operate. 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.

These are all signs the battery is down on charge. Load test the battery to confirm its condition which can be done using and observing the headlights of the car and by watching the video below. If the battery warning light is not on while driving this means the battery is probably being charged properly and it has lost its ability to hold a proper charge. 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.

Battery Test Video

If the battery tests bad and the battery light has not been on then the battery needs to be replaced. 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 replacement. 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. 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. Here is a video on how to replace your battery.

Battery Replacement Video

If in the dash the battery warning light has been on prior to this repair and the battery is fairly new then the battery will need to be jumped to get the engine running so the alternator can be checked. 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. This step is necessary to test the alternator which will be in the next video.

Battery Jump Video

Test the alternator voltage output once the engine is running. If the alternator fails this test then it will need to be replaced.

Alternator Test Video

2. Check Battery Cable Connection

The battery supplies voltage to the starter through positive and negative battery cables which need to be clean, tight and free from corrosion. If you know the battery is good because it is fairly new or you have tested it has passed there could be a battery connection 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. Corrosion and loose connections stop electrical current flow. When this condition occurs the car will act much like a low 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. These conditions cause heat which will produce the power disconnect. When the connection cools it can start working again. Inspect the battery cable ends for corrosion which means they need to be cleaned. 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.

3. Check Starter Fuse and Relay

Like most heavy electrical load components such as starter there is a fuse and relay to protect the circuit. These components are usually located in the fuse panel or power distribution center under the hood. If the fuse fails it will cause 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. Use a grounded test light and locate the fuse panel to test the fuse. Replace any that have failed and recheck the starter operation. If the fuse tests okay continue down the guide.

The starter relay is next in the circuit to supply power to the starter solenoid which engages the starter motor operation. Some older 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 owner's 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.

4. Test the Starter Solenoid 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 most 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. Connect 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. Then 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 hear 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. If the starter is getting power and still not working you can try using a hammer while the ignition key is held in the crank position and bang on the starter. This will get the starter to sometimes work one more time.

Starter Replacement Video

5. Starter Makes Noise But Still Not Cranking

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 fix the problem. 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 (standard transmission) or flex plate (automatic transmission). The small gear contacts the large gear only when the starter is engaged and then retracts after the engine starts. The solenoid is an electromagnetic 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 completely into the flywheel which then creates a grinding noise 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 flywheel must be replaced before installing the new starter. Below is a picture of the flywheel on the rear of the engine with the transmission being removed.

Flywheel Replacement Video

6. 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 depressed. This safety feature will not allow the engine to start while the transmission is in gear which will make the car take off unexpectedly when the engine starts. Both of these switches are subject to wear and can become misadjusted 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 lodged 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 then works the neutral safety switch has gone bad and needs adjustment or replacement.

7. 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 this problem remove the serpentine belt and check to see if each of an accessory 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 serpentine belt the try the starter. If the engine will still not turn over, 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.

Got Any Questions?

If you have any engine not starting questions or not cranking over questions, please visit our forum. If you need car repair advice, please ask our community of mechanics is happy to help you and it is always 100% free.

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