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What’s wrong with my car? Common reasons it won’t start

Practical Motoring logo Practical Motoring 02-08-2017 Alex Rae

Turning the key in the ignition and hearing… nothing… is a horrible feeling, but don’t panic. Follow our guide to self-diagnosing what’s wrong with your car.

BEFORE GOING ANY FURTHER: Is there fuel in the car? Is the automatic transmission in park and a foot is on the brake? Is the clutch depressed if it’s a manual?

Okay, with that out of the way, next diagnose if it’s an electrical fault or fuel problem. Most problems are electrical related, and if the car isn’t turning over or is turning over very slowly it most certainly is. So let’s start there.

The following should be used as a guide only and, as ever, if in doubt, call a mechanic. Much of the following is aimed at owners of older vehicles and assumes a certain level of mechanical knowledge.

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Car won’t turn over

Battery might be dead: This is easy to diagnose because you’ve probably left the headlights on or the keys in ignition for a long time.

Check: Do the headlights turn-on to normal brightness? Is the radio dead? If so, the battery has probably lost charge. If the battery is leaking, covered in corrosion or damaged then you’ll need a new one, don’t attempt to jump start it.

Jump-start: 

WARNING:This advice applies only to older vehicles as modern cars have complicated and advanced electrical systems that can be damaged by attempting to jump-start them. So, in this situation, if you suspect your car's battery is at fault, don't try and jump start it, call your road-side breakdown service who have service vehicles equipped to deal with modern vehicles. That said, one thing owners of new vehicles can do, is remove the battery completely from the vehicle and, if they have a charger, charge the battery away from the vehicle and then replace it once charged.

ALSO READ: Everything you need to know about changing car tyres…

If the battery appears in good condition the best case-scenario is getting a jump-start from another car. You’ll need jumper leads and a running car. Connect a positive lead clamp to the positive terminal on the running car’s battery, and then connect the other positive lead to the dead battery’s positive terminal. Next, connect the negative lead clamp to the negative terminal on the running car, and then connect the other negative clamp to an earth point on the car - NOT the dead car's battery, or as directed by the owner's manual.

Wait a minute before trying to start the car. If the car won’t turn wait a little longer. Make sure the jump leads don’t get too hot. If the car still won’t start the battery has either expired or there’s another problem.

Deep charge if possible: Trickle chargers for 12v car batteries are cheap and good to have in the shed. If the battery has lost too much charge it’s a good idea to give it a proper deep charge - follow the instructions provided with the charger.

My battery keeps going flat: If the battery is old then you probably need to consider replacing it. A car battery will usually last four to five years, however extended use in very cold weather can decrease its life.

If the battery is within its lifespan, the alternator may be faulty. The alternator is responsible for charging the battery and it can wear out over time. Also check the belt running it is in good condition, as this may be the issue. If not, a replacement alternator might be the solution. Replacing the alternator is a more advanced DIY.

<p>Turning the key in the ignition and hearing… nothing… is a horrible feeling, but don’t panic.</p> © Provided by Practical Motoring

Turning the key in the ignition and hearing… nothing… is a horrible feeling, but don’t panic.

Battery is charged and alternator is fine, but car won’t turn over: The starter motor might be broken or faulty. Usually it will show signs of wearing out by not turning consistently before it completely fails. If the starter motor is suspected, use a maintenance manual to located the starter motor and try tapping it with the end of a hammer while someone else attempts to start the car.

IMPORTANT: Do not attempt if not safe to do so and never put any part of your body in danger.

If the car starts the starter motor is on the way out - better to replace it now before it completely fails. Further diagnosis of the starter motor is dangerous as high voltages are present - it’s best to take the car to a mechanic at this point.

The car is turning but not starting...

If the car is turning over but not starting, there might be not spark inside the cylinder to ignite the fuel. To check for spark you’ll need to remove one of the spark plugs. Once out connect the spark plug into the lead socket and place the metal electrode end of the plug 2-4mm from a metal part of the engine. Alternatively use a spark tester.

IMPORTANT: Do not place near fuel and do not hold the plug with your hand, you’ll likely get an electric shock.

Turn the car over (you might need and helper) and if there’s is a spark then the problem is probably the fuel system. If there’s no spark the problem is elsewhere in the ignition circuit.

Change spark plugs: Inspect the spark plugs, they will be tarnished from use but should not be corroded, covered in oil (if they are, go see your mechanic), or caked with deposits. If they are overly dirty they will need replacing.

Ignition problem: The ignition contact may have worn out, but it’s rare. If this happens the dash lights will flicker when turning the car into ignition like there’s a bad connection.

Distributor or ignition module faulty: More likely is that the distributor or ignition module is faulty and not sending spark to the plugs. To check, remove the lead connected to the distributor or ignition module and connect a voltmeter and turn the engine. If the lead is producing voltage, the problem is likely the distributor or ignition module.

If there’s no voltage the problem could be a fault from sensors in the car - at this point the car should be taken to a workshop to have the computer diagnosed for fault codes and fixed accordingly.

The electrical system seems fine; I think it may be a problem with the fuel

Turn the car over a few times and remove a spark plug. Is it wet with fuel? This is not a completely accurate method to test if fuel is being delivered to the engine, but it will provide a good indication. If there’s fuel in there, the fuel might be bad, if there’s no fuel, the issue is probably a bad fuel pump or clogged filter preventing the fuel from pumping.

Bad fuel: When did you last fill the tank? Fuel goes off, so if it’s old you’ll need to drain the tank and replace with new fuel. If the fuel is brand new, you might have received a bad batch. You’ll also need to drain the tank and replace.

To drain the fuel tank, check a maintenance manual for instructions, or better yet, have your mechanic do it for you - it’s a dangerous job and not for the average DIYer.

No Fuel

Fuel pump might be faulty: The pump can be heard near the fuel tank priming for around 5 seconds when the key is placed into ignition. It might be best heard from within the boot. If there’s no sound, the pump might be broken or not receiving power. If you’re keen to investigate further, use a maintenance manual to locate the fuel pump and check again. If it’s not operating when turning the car, disconnect its power terminals and then check the wires for voltage. If there’s voltage, the pump has probably had it. In newer cars, a faulty fuel pump should show as a fault on the computer diagnostics - much easier.

If the car is older and carburetted, disconnect the fuel hose leading into it and place into a large container. Turn the car over briefly and fuel should pump. If it does, the carburetor might be this issue, if not, the mechanical fuel pump is probably broken.

Check the fuel filter: It’s possible the fuel filter is clogged, but most filters can’t be inspected as they are enclosed. The fuel filter on older vehicles is usually located underneath the car and is reasonably easy but messy to replace. Newer cars have the fuel filter inside the tank or integrated as part of the fuel pump. If the car is serviced it should be part of the service program and it’s recommended to have a mechanic inspect this, unless you are a confident DIYer - in which case refer to a maintenance manual for instruction on how to access and replace the fuel filter.

Other problems...

It’s possible the fuel injectors are faulty, however this usually results in the car starting with a rough idle.

A fuse may have blown that’s needed to start the car, such as for the fuel pump, starter motor or ignition. Check the fuses - there’s usually one in the engine bay and one inside the cabin. Refer to the owner’s manual.

Nearly all modern cars have a socket under the dash to plug in a diagnostics tool. This will show fault codes and will make finding the fault much easier. Most cars use an OBD2 tool, which can bought, however many mechanics and some auto parts stores will check this for free.

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