It’s no secret that today’s modern vehicles are more complex than ever. Between the many sensors that regulate the functionality and emissions of our engines, to computers communicating over Controller Area Network (CAN) systems, it’s very easy to get overwhelmed. 

However, if we take a deep breath and remember the basics, diagnosing these systems will be much easier and make a lot more sense. Even when discussing today’s most complex engines, there are still only five things (in no particular order) that they need for them to run. 

First, a car needs fuel. Not just in the tank, but the entire delivery system. Make sure the injectors are firing and that they have the proper fuel pressure. Every manufacturer has its own procedures for testing this, so make sure you check your service information regularly.

Second, the engine will need a way of igniting this fuel, which leads us to ignition. When addressing the ignition system, make sure you include the entire system – which includes, but is not limited to, ECM control over the ignition coils, wires (if equipped) and spark plugs. 

Third, make sure the engine is getting its proper amount of air. A clogged engine air filter could result in a poor running engine, and a completely plugged filter will result in a no start condition. I remember working on a vehicle that had sucked a plastic bag up into the airbox, which completely sealed the air intake, and choked the engine.

Fourth, in order to create the pressure needed to push the piston downward during the power stroke, which ultimately spins the crankshaft, we need compression. Without compression (which is a combination of piston rings sealing properly inside the cylinder bore and the starter motor spinning the crank to push the pistons to top dead center (TDC)), there would not be enough energy created during combustion to start the engine.

Lastly, all of these things must happen at precisely the right time! The injectors must deliver fuel, and the spark plugs must fire at a precise degree of crankshaft rotation for the 4-stroke cycle to function properly. Timing also includes the synchronization of the camshaft (which controls valve activity) to the crankshaft (which controls piston activity) by way of a timing belt.

I promise you, if your engine has satisfied the above criteria, the engine will run. 

Understand that the purpose of the numerous sensors and computers found in a modern vehicle are designed to ensure all of these criteria happen properly, efficiently and effectively. For example, if the crankshaft sensor were to malfunction and not send a signal to the ECM/PCM, the vehicle may not start because the computer relies on that signal to determine spark (which is one of the basic criteria). As another example, if the camshaft sensor were to not deliver a signal to the ECM/PCM the vehicle may not start because the vehicle needs that signal to determine fuel injector activity to deliver fuel (another one of the basic criteria).

It all boils down to the basics!