Diagnose: Why Won’t My Car Start (updated)

It’s a Monday morning, you are late out the door, you get in your car and try to turn it on. Surprise! It won’t start! Do you know how to figure out what’s wrong with your automotive pet? If you have no idea where to begin, it sure will be difficult to repair it.
There are a lot of reasons why your car won’t start:
– 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.
Here is what you can do to get to the bottom of why your car won’t start. Check the car battery first before worrying about the starter motor, fuel pump, or ignition repairs. Experts will tell you that a lot of the time, the car simply needs a new battery. When you are sure, the battery is not the problem or put in a new one, investigate the other possible faults.

How old is your car battery?

When diagnosing why the car is not starting, do the battery eye test. Safety first, so apply the parking brake and make sure the ignition is off. Lift the hood and look for corrosion around the cell connectors, cracks down the side or on top of the battery, frayed or broken cables, or unusual stains. If you see most of these on the battery, then you know the reason for your car starting problems, and it is time to get a new car battery. But how do you swap the battery yourself?
Before you remove the battery, use your smartphone to take a photo of the battery compartment. It will help you remember how to reconnect the new battery, especially if you have never done it before. It is always best to have experts replace the battery, but if you are determined to do it yourself, let’s look at the next steps.
Disconnect the black (negative) cable first, then the red (positive) cable. If you disconnect the red cable first and touch any metal surface, you could create a spark that damages the electrical system. The battery is kept safe by restraints that are either a clip holding it in place at the bottom or a bar on top. Remove the restraints with a wrench and lift the battery while keeping it level.
If you see dirt, give the area where your old battery was a quick wipe. Put the new battery in and fasten the restraints. Now you must reverse the cable steps. First connect the red cable, then the black cable. The new car battery should be fully charged when you buy it. Take the old battery for proper recycling to the store where you got the new one.
What else can cause a car not to start when you put in a new battery?

Is the engine cranking?

The first thing you should check is whether the engine is cranking or not. If you know your engine is cranking, you can go to the next step. You can typically hear it from the starter’s sound when turning the ignition. If the car is not cranking when you are turning the ignition switch to the start position, you may have a low voltage or a starter problem.
If your engine is not cranking, ensure that the car battery is charged and in working order. You can either try to jump-start the battery from another car or with the help of a booster pack. You can also work with a different car battery if you have an extra one at home.
If the battery is good and the jump start didn’t help the engine to crank, there is most likely a problem with your starter or the electrics to it.
The next step is to test the wires on the starter. A starter usually does have two wires connected to it: one large b+ wire and one small.
Check the ground between the engine and the body. You can put a jumper cable between the battery negative terminal and a good ground point on the engine to check if it’s bad ground.
Check if you have 12V on the large wire on the starter with a multimeter.
Check if you get 12V on the small wire when you are turning the ignition switch to the starter position. Keep your hands away from any moving parts while doing it!
If you have 12V on both the wires and the ground is right, there might be an ampere problem in the large wire or a faulty starter. It’s rare for the massive power cable to the starter to get damaged, so to be 100% sure that’s the cause, you have to perform a loading test on the wire.
If you have done a loading test and it shows OK, and you get 12V on the small cable when cranking, you have a faulty starter, and it has to be replaced.
If you are not getting 12V on the small wire when you have the ignition switch in the starter position, you have a problem with the starter signal, and you have to troubleshoot the ignition switch, starter relay, fuses and the wirings between the ignition switch to the starter.

Check the trouble code memory

If the car is cranking, but won’t start, use an OBD2 scanner to find out if there are any stored trouble codes in the trouble code memory. By reading the trouble codes, you can skip over many troubleshooting steps and jump directly to troubleshooting the part you got the trouble code for.
Most cars after 1998 have an OBD2 system which makes it very easy to read the trouble codes. You can find the information about the trouble codes in the OBD2 codes. If you have an older American vehicle, there is a chance that you have OBD1 codes and you do not need a scanner to read them.

Check the crankshaft/camshaft sensors

The next step is to check the RPM signal from the crankshaft and the camshaft sensor. You can do this by checking your tachometer for any RPM readings on the dashboard. Even better is to check the value of the crankshaft RPM from the engine control unit with an OBD2 scanner. In most cases, you will get a trouble code on the crankshaft or camshaft sensor if there is a problem there.
In 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 make corrections if you are getting any RPMs in the engine control unit and make sure there are no trouble codes stored.

Check the fuel pressure

Now if the crankshaft and camshaft sensors seem okay, it’s time to check if you have any fuel pressure. A bad fuel pump, clogged fuel filter or a bad fuel pressure regulator can result in low fuel pressure which will lead to your car might not starting. Low fuel pressure is a widespread cause of why your car won’t start.
You can either check the fuel pressure with a fuel pressure gauge or check it in the OBD2 scanner if your car is equipped with a fuel pressure sensor. If it’s equipped with a fuel pressure sensor, you will likely also get a trouble code showing low fuel pressure. But it’s always good to verify it with a manual fuel pressure gauge.
If the fuel pressure is low, check the wirings, relay and fuse to the fuel pressure pump and test if it’s pumping any fuel. If it’s not going, but you get voltage to it, replace the fuel pump. If the fuel pump is fine, replace the fuel filter and troubleshoot the fuel pressure regulator.

Check the spark from the ignition coil

Spark is another common problem when the car won’t start. It could either be caused by a bad spark plug, bad ignition coil or ignition cable. The wirings could also point to the ignition coil or to no signal from the crankshaft sensor, so you should always diagnose the crankshaft sensor first.
You can check the spark by removing the cable/coil and the spark plug. Take a cable between the plug and a good ground point and let a friend crank the engine while you are checking for a spark, just remember to keep your hands away from the spark or you will get a dangerous shock.

Check if the injectors are opening

Another common cause – is the injectors are not opening and injecting fuel into the engine. A broken fuse/power wire is usually to be blamed, but in rare cases, it can also be produced by a bad engine control unit.
You can measure the voltage with a multimeter to check if the injectors are opening. The injectors usually do have two pins, one 12+ power and one ground signal to the engine control unit. Make sure you have 12V on one of the wires while cranking and you can check if you get any ground signal with an LED light. More advanced troubleshooting of the injectors should be done with an oscilloscope.
When the fuel injectors are opening, they are often making a small clicking sound which you can hear if you listen carefully. Let a friend crank the engine and check if the injectors are clicking. If they are clicking, the injectors shouldn’t have a problem. You can also take a look at the spark plugs – if the car is injecting fuel, they will be wet but produce no sparks.

Check the crankshaft/camshaft timing

A lousy timing belt or a bad timing chain can result in serious engine damage which can make your car not want to start. Almost all engines have TDC marks where the camshaft and the crankshaft should be aligned. You have to find these marks either in the repair manual for your car or online. Then you have to check if the timing is correct.
A timing belt or a timing chain that has jumped over will in almost all vehicles result in damaged valves. If you suspect that your chain or belt has skipped over, you should always make a compression test to verify that the compression is good and the valves are not bent.

Check compression/leak down test

If you have fuel and ignition working, but the car still won’t start, the last step is to check compression and leak down through the piston rings. First, you should make a compression test with a compression tester to verify that you have the same pressure on all cylinders. Check the repair manual to see what pressure the engine should have. Worn engines can have slightly lower pressure, but the pressure should be even between the cylinders.
A leak-down test is meant to help you see if there is any pressure going through the piston rings down to the bottom of the engine. This can be a good method to recognize broken pistons and piston rings.

Check the fleet car in when it won’t start

When the car that won’t start is one of a fleet, it is better to contact the professionals for help. Your company will have rules when there is a fleet car breakdown or it does not start. They want you to be safe and for you to deliver the service or goods to clients on time. CRS Automotive Hamilton has a fleet service team that prioritizes starting your company car.

If all this is too much for you, come to our repair shop in Hamilton. We will take good care of your car.