An attempt is made to turn the car on but either nothing is happening, a clicking sound is heard, or the starter is turning the motor but the engine won't start. The problem could be as simple as a dead battery or as complex as a bad fuel pump or neutral safety switch. One tool that is absolutely essential to diagnose the issue is a multimeter. An inexpensive multimeter can be purchased at Radioshack for under $20.
No Crank, No Start
In this scenario, either the starter is clicking or nothing is happening. Try turning the lights on. If they are dim, then this is an indicator that the battery is dead and needs a jump or recharge. If the lights aren't dim, then there is another issue. Use a multimeter to check the voltage on the battery. To do this set the multimeter on the Volts setting and connect the red lead to the positive terminal and the black lead to the negative terminal. There should be 12 Volts at the battery. If there isn't, recharge the battery or jump the car.
If the voltage is fine, attention should be turned to the starter The goal is to find out if the starter is getting a signal. If the starter is getting a signal, then we know the starter is bad and needs to be replaced, which can also be verified by removing the starter and getting it bench tested at an automotive parts store. To see if the starter is getting voltage:
Another issue that plagues many vehicles is corrosion. Be sure to check the battery terminals for corrosion, as well as the negative battery cable where it attaches to the body. If there is any corrosion there, that could be the cause of the vehicle not starting.
Crank, No Start
The car is cranking, meaning you can hear it trying to start, but it just won't turn over. An engine needs fuel, spark, and compression to start. If it doesn't have any one of these, it will not run.
Testing for spark is by far one of the easiest tests to perform. To test for spark, follow these steps:
If spark is available, check for fuel. There are a couple ways to do this. One is by using a fuel pressure tester and plugging it into the port on the fuel rail. If a fuel pressure tester isn't available, test for fuel by following these steps:
Was there a heavy stream of fuel exiting the fuel line? If so, the fuel pump is good. If not, try replacing the relay. If that does not fix the problem, then a faulty fuel pump is the cause of the vehicle not starting. If fuel is available, then the issue could be one of the fuel injectors. Pull out the digital multimeter and set it to the "ohms" setting. Unplug the fuel injectors one by one and check for resistance. Each injector should have a very low reading (0-15 ohms). If the multimeter reads more or reads "infinite", then the injector is faulty and should be replaced.
If spark and fuel checked out fine, then the only conceivable problem is compression. To verify this, obtain a compression tester to test each of the cylinders and follow these steps:
What is the reading at? Obtain the compression specification from the dealership or factory service manual and compare to the reading. Are the readings consistent or is there one or two readings that are way below the rest? If one or two readings are way below the others, an engine rebuild or replacement is necessary. If compression checks out, then follow this guide again making sure you followed it precisely.
Diagnosing a vehicle no start, as can be seen, is very methodical in nature and only requires a following of an established guide to finding the fault. Unless the vehicle that is being worked on has a very rare issue, the chances are that this guide will help pinpoint the issue.