Car Won’t Start: Basic Diagnostic Tests

There are three essentials that must be in place for gasoline and diesel engines to start: spark, fuel and mechanical soundness or compression. Begin your diagnosis by exploring all three areas one step at a time to discover your car won’t start problem. We will examine the most common problems only or what any driver can usually handle without the mechanical expertise to show for it.

car diagnostic


Locate your car’s battery and check the posts and cables. The connections should be secure and free of corrosion. If corrosion is present, a solution of water and baking soda along with a wire brush can clean the contacts. Jump start the car if the battery is dead.


Verify that your car has fuel. The fuel gauge may incorrectly show that you have a gallon or two of fuel left in your car, but it may be empty. Without fuel, the engine will not generate spark to start, therefore put in a gallon of fresh fuel and try the ignition again. If it turns over, head to the nearest service station and top off the fuel tank. Replace the fuel gauge fuse if this has burned out.

Mechanical Soundness

Examine the timing belt. Your car’s engine may have clean fuel and sufficient oil, but it won’t turn over if the timing belt is no good. Through observation you can usually discover whether the belt is broken or loose. You can also rotate the timing belt slightly to determine whether it is loose. If loose or broken, replace it immediately to avoid costly engine repairs.

Diagnostic Codes

Look up the OBD code. If the starter cranks and the engine does not turn over or its starts and then stalls out, your dashboard should hold an important clue. Specifically, the check engine light will activate, indicating a problem. If the light is flashing you need to contact your mechanic. If the light is solid, an onboard diagnostics tool reader (OBD-II scanner) can identify the problem. Connect the scanner to your car’s 16-pin connector, typically located underneath the dashboard. Check your service manual for the location. Write down the read out code and find that code in the related book. If the problem is something you can handle such as replacing the engine coolant temperature sensor, then replace it. If the repair is beyond your expertise or comfort level, then contact your mechanic.

Photo Attribution

Photos by Tim Samuel via

See AlsoNew Car Windshields – Proper Care and Maintenance Tips

Matt Keegan
Author: Matthew Keegan
Matt Keegan is a journalist, media professional, and owner of this website. He has an extensive writing background and has covered the automotive sector continuously since 2004. When not driving and evaluating new vehicles, Matt enjoys spending his time outdoors.

Leave a Reply

Your email address will not be published. Required fields are marked *