Car hesitates to start. What are the causes

Sometimes drivers experience difficulties when starting the car, often these problems occur in cold temperatures, especially on diesel engines that are more sensitive to these conditions.

The reasons why the car hesitates to start depends on the type of engine the car has because the reasons why gasoline engines have this problem differ from the causes that are found in diesel engines.

Also, we should take into account the situations when the car hesitates to start, such as when the engine is warm or this happens when the engine is cold, and the car sits for a short or long time.

In this article, we will list the main causes that lead to a hard engine start. Usually, one or two rotations of the starter shaft are enough to start a car in good condition. If this cannot be done, it is advisable to look for potential problems.

The battery is worn out.

If the battery is about to fail, it will not give the right amount of energy that the engine needs to start correctly, leading to a hard engine start, or the engine might not start at all. This is a common cause and it can happen very often in the cold season.

The starter seems to be turning but the car either has a bad start or does not start at all, the reason being a voltage drop at startup. An old or failing battery cannot provide this. This does not happen on a warm engine.

Also, there can be leaks in the car’s electrical system that drains the battery even if it’s new. This can be caused by a bad wire or components that are connected to the electrical system such as alarms, radio, video cameras, etc. Check these items first to see if you have leaks.

The spark plugs are bad

Failing spark plugs are one of the most common reasons why your car hesitates to start. This can happen especially if the electrical connections of the ignition system are damaged or if the ignition coil is failing.

If you do see problems with the spark plugs then you need to change them.

Low-quality gasoline

Adding low-quality fuel to your tank can cause more problems than you think. It can cause the spark plugs to fail, clog the injector, and even cause significant damage to the engine in case of incorrect detonation. If you add low-quality gasoline, and your car starts to experience hard starts, adding some fuel additives may help.

Problems with the air filter

The car can hesitate to start because of the air filter, especially if not enough air enters the engine. This lack of air is caused mostly by a clogged or dirty air filter. But the air filter can be blamed mostly. This problem is caused by the air filter more often in winter because of high-temperature changes.

Air leaks

Starting the car depends on the outside temperature, If the temperature is low, then more air is needed for starting. Before that, the ECU, based on temperature readings, opens de idle air control valve. Because the ECU takes the air values from its memory, it does not know about the extra air and this will result in a hard start, maybe after some attempts.

In this case, you should check the intake for air leaks. Most of them are found through crankcase ventilation valve and because of worn-out gaskets fount between the intake manifold and the engine.

A bad camshaft position sensor

Based on the signals received from the camshaft position sensor, the ECU sets the ignition timing and the cylinder to which the fuel should be supplied. Therefore, if an incorrect signal from the camshaft position sensor is given, the engine will not start the first time.

Very often the problem is not the sensor itself, but its incorrect installation and wiring. A strong symptom of a bad camshaft position sensor is the smell of gasoline.

A bad crankshaft position sensor

If the crankshaft position sensor is failing the car will start anyway because the engine can operate without it, but it will need more time to start. Often a faulty crankshaft position sensor is caused by metal material present on the sensor and a quick and easy way to solve this problem is by removing the sensor and cleaning it.

Bad or failing purge valve

The role of the purge valve is to not allow the fuel vapors created in the fuel tank to get into the atmosphere. If the valve is faulty or leaking, this can mean that fuel vapors can get into the intake manifold and engine cylinders.

Because of that, there will be an excess of fuel and the engine will hesitate to start on the first attempt or it will have a difficult start. A sign that can indicate this problem can be a floating idle or dips in idle speed.

A bad starter

A failing starter can also cause the car to start hard, even if the battery is in good condition.

Low compression in diesel engines

Often caused by wear of the cylinder-piston group. During operation, carbon deposits, sludge, and varnish contamination will form inside the engine. 

The process is inevitable, over time a situation arises when carbon deposits do not allow the compression rings to work correctly. Compression falls, and the pressure becomes insufficient to ignite the fuel mixture.

To prevent this situation from getting worse it’s best to clean the carbon buildups by performing an engine flush.

The electronic control unit (ECU) might not work properly

This can also be a reason why the car hesitates to start. If the ECU is malfunctioning it can lead to this problem, although this is rare.


There are quite a few reasons why the car can have a hard start. As preventive measures, you can check the car battery from time to time and change it if you notice a bad car start in colder temperatures.

When carrying out maintenance, inspect the condition of the car’s electrical circuits, clean them promptly, and use special protective equipment.

Check the functionality and condition of the sensors, especially the camshaft position sensor and crankshaft position sensor.

Their incorrect operation is often a problem, due to which the engine does not start well when hot. When carrying out the replacement procedure, go to a good car workshop. It’s better that way.

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