Trying to fix a car that won’t start can be one of the most difficult troubleshooting tasks when you don’t know where to start.
I work as a diagnostic technician, and advanced troubleshooting is my daily job. I have developed a system that I provide free of charge to help you troubleshoot a car that won’t start.
This guide consists of 10 steps, and I recommend that you follow them carefully to find the problem with your car in the fastest way.
We’ll start with some common reasons why your car won’t start and then move on to the troubleshooting steps.
Common causes why a car won’t start
There are many different reasons why a car will not start. Here is a list of the most common reasons why a car won’t start. Don’t just replace parts, look further down the article to repair your car correctly.
- Faulty Starter motor
- Low voltage/Bad car battery
- Bad Fuel pump
- Faulty Crankshaft Sensor
- Faulty Ignition coil
- Faulty Ignition Switch
- Faulty Ignition Relay / Main Relay
Car Won’t Start: Troubleshooting
|Car Won't start||Starter motor|
Low voltage/Bad car battery
Ignition Relay / Main Relay
|Check starter motor |
Check battery voltage
Check fuel pressure
Check RPM signal
Check trouble codes
Check ignition coils
Check spark plugs
Check ignition switch
Check crankshaft sensor
Check camshaft sensor
Check camshaft timing
Car Won’t Start Diagnose Guide
1. Is the engine cranking?
The first thing you should do is check whether the engine is cranking or not. If you know that your car is cranking, you can move on to the next step. You can usually hear it by the sound when you turn the starter. If the car does not crank when the ignition switch is turned to the starting position, there may be a low voltage or a problem with the starter.
- If your engine does not start, make sure that the car battery is charged and has not failed. You can either try to start it from another car or with the help of a jump starter. You can also use another car battery if you have one at home.
- If the battery is OK and the jump starter has not helped the engine start, there will most likely be a problem with the starter motor or the electrical system of the starter. A tip: Tap the starter with a hammer at the same time as a friend or other person tries to start the engine. This can help the carbons to jump to the right place in the starter and start it. If the starter motor cranks when knocked, there is a problem with the starter motor and it is recommended that it be replaced as soon as possible.
- If tapping has not helped, you must measure the wires on the starter. There are usually two wires connected to a starter: a large b+ wire and a small one.
- Check the ground between the engine and the body. You can place a jumper cable between the negative pole of the battery and a good ground point on the engine to check if there is a bad ground.
- Use a multimeter to check that you have 12 volts on the large cable at the starter.
- Check that you have 12 volts on the small cable when you turn the ignition switch to the starting position. Keep your hands away from all moving parts!
- If you have 12 volts on both wires and the ground is correct, there could be an ampere problem in the large wire or a defective starter. It is rare for the solid power cable to the starter to be damaged and to ensure that the voltage is 100%, you must perform a load test on the cable.
- If you have carried out a load test and it is OK and you get 12 volts on the small wire when starting, you have a defective starter that needs to be replaced.
- If you are missing 12 volts on the small cable when you have the ignition switch in the starting position. You have a problem with the starter signal, and you need to fix the ignition switch, the starter relay, the fuses and the wiring between the ignition switch and the starter.
2. Check the trouble code memory
If the car cranks but does not start, the best way to find out if there are any error codes stored in the error code memory is to use an OBD2 scanner. By reading the error codes, you can skip most of the troubleshooting steps and jump directly to the part for which you received the error code.
Most post-1998 vehicles have an OBD2 system in the vehicle, which makes reading the fault codes very easy. You can find the information about the fault codes in the OBD2 codes. If you have an older American vehicle, it is possible that you have OBD1 codes and you do not need a scanner to read these types of error codes.
If you have any further questions about the fault codes you have received, please contact us and we will help you with where to start troubleshooting.
3. Check the crankshaft/camshaft sensors
The next step is to check the RPM signal from the crankshaft and camshaft sensor. You can do this by checking your tachometer to see if you have any RPMs displayed on the dashboard. A better way is to check the value of the crankshaft speed from the engine control unit with an OBD2 scanner. In most cases you will get an error code on the crankshaft or camshaft sensor if there is a problem there.
For more advanced troubleshooting you can also check the signals from the crankshaft and camshaft sensors with an oscilloscope to see if the signal looks good or not, but in most cases you can only correct if you get some RPMs from the engine ECU and make sure that no error codes are stored.
4. Check the fuel pressure
If the crankshaft and camshaft sensors seem to be okay, it is now time to check if you have fuel pressure. A poor fuel pump, clogged fuel filter or poor fuel pressure regulator can result in low fuel pressure, which may cause your car to not start. Low fuel pressure is a common cause of your car not starting.
You can check fuel pressure either with a fuel pressure gauge or with the OBD2 scanner if your vehicle is equipped with a fuel pressure sensor. If it is fitted with a fuel pressure sensor, you will most likely also receive an error code stored indicating the fuel pressure is low. But it is always good to check this with a manual fuel pressure gauge.
If the fuel pressure is low, check the wiring, relay, and fuse of the fuel pressure pump and test if it is pumping fuel. If it does not run, but you get power, replace the fuel pump. If the fuel pump is OK, replace the fuel filter and correct the fuel pressure regulator fault.
5. Check the spark from the ignition coil
Another common problem when the car does not start is problems with the spark. It can be caused either by a bad spark plug, a bad ignition coil, or a bad ignition cable. The wiring could also cause problems at the ignition coil or no signal from the crankshaft sensor, so you should always diagnose the crankshaft sensor first.
You can check the spark by removing the wire/coil and spark plug. Take a wire between the plug and a good ground point and have a friend start the engine while you check for sparking.
In this video you will learn a little more about how to check the spark of an engine:
6. Check if the injectors are opening
Another common cause is that the injectors do not open and thus fail to deliver fuel to the engine. A broken fuse/wire or lack of signal from the crankshaft sensor usually causes this to happen to the injectors. In rare cases it can also be caused by a bad engine control unit.
To check if the injectors open, you can measure the voltage with a multimeter. The injectors usually have two pins, a 12+ power, and a ground signal to the engine ECU. Make sure that you have 12 volts on one of the wires when starting, and you can use an LED light to check if you get a ground signal. Further troubleshooting on the injectors should be done with an oscilloscope.
When the injectors open, they often produce a small click that you can hear if you listen carefully. Let a friend start the engine and check if the injectors click. If they click, the injectors should be OK. You can also see from the spark plugs whether the car is injecting fuel, as they often get wet when you get fuel but no spark.
7. Check the Crankshaft/Camshaft timing
A lousy timing belt or a poor timing chain can cause serious engine damage, which can prevent your car from starting. Almost all engines have TDC markings where the camshaft and crankshaft should be aligned. You must either find these marks in your car’s repair manual or find out online. Then you have to check if the timing is correct.
A skipped timing belt or timing chain causes damage to the valves in almost all cars. If you suspect that your chain or belt is skipped, you should always do a compression test to check that the compression is good and that the valves are not bent.
8. Check compression/leak down test
The last step, if you have fuel and ignition, but the car still won’t start, is to check the compression and check the leakage through the piston rings at the bottom. First you should do a compression test with a compression tester to make sure that you have the same pressure on all cylinders. Refer to the repair manual to find out what pressure the engine should have. Worn engines can have slightly lower pressure, but the pressure should be even between the cylinders.
A leakage test checks whether the pressure is flowing through the piston rings to the bottom of the engine. This can be a good method of detecting broken pistons and piston rings. If you want to check our leakage down tester, you can find it here at Amazon: Leak down tester
In the video below you will find a more detailed description of how to perform a compression test at home:
An engine needs fuel, ignition, camshaft control and compression to start. If you follow these diagnostic procedures, you will most likely find the problem of why your car won’t start. If you start checking the fault codes, you can significantly reduce the troubleshooting time by getting a code indicating where to start troubleshooting. If you want to have a scanner at home to read the fault codes from the engine control unit, you can take a look at our guide to OBD2 scanners.
If you have further questions about the car, you can ask them on our homepage. If you have problems getting your car to start after this article, please comment below and I will answer you as soon as possible. You can also discuss it and tell us how you repaired your engine when it wouldn’t start.