Basic Car Engine Parts Diagram

Beginner's Guide to Car Engine Diagnostics

Last Updated March 25, 2020

How much do you know about engines? The average person only knows how to carry out basic maintenance, like changing the oil and topping up the radiator. So what do most of us do when the motor makes strange noises or the dash begins to light up with warnings? Problems like misfiring cylinders and damaged suspension are easy enough to diagnose because of the noises they make but modern cars need to go through a diagnostic machine to work out what exactly is wrong with them so you'll probably be heading to the auto shop if your motor's not running smoothly.

Car Engine Diagnostics

Every new car sold in the USA since 1996 has been installed with an on-board computer that monitors parameters like speed, voltage and temperature. It also takes stats from braking and steering as well as other actions. When something outside of normal operating parameters is detected, the on-board computer's software turns on the dashboard warning lights. Until recently you had to take your car to the garage to find out what was wrong with it but you can now buy handheld scanners that plug into your car and tell you what's wrong with your car.

The plug point for OBD-II, which has been the standard on-board diagnostics device fitted to cars and light trucks since 1996, is found close to the driver seat in all cars. It's normally behind a trim panel or between the front seats, although Honda drivers will find theirs by the ashtray. Your scanner is designed to connect to the car through this port. When it's plugged in, turn the ignition on but don't start the motor. The device will ask for your vehicle identification number (VIN), the engine type and the car's make and model. Just follow the onscreen instructions. Now press the 'Read' button on the scanner. If you get any error codes, write them down.

Resetting Engine Lights

The most expensive scanners will bring up information about the fault. Other devices will point you to a CD that came with it or a website where you can get a breakdown of the fault by inputting the code. That's great but if you diagnose the issue at home and correct it yourself, the dashboard warning lights will still be on. You can reset these lights yourself through the scanner. Attach the scanner to the car as instructed earlier and run it as before. When the error codes come up press 'Clear' or 'Erase' and they'll disappear.

Powertrain Control Module

Although you've turned off the warning lights, the powertrain control module (PCM) needs to record data from various sensors before it can be satisfied that the fault's gone for good. Until this is complete your car won't pass any inspection and maintenance test at the Department of Motor Vehicles (DMV). That's because the DMV doesn't want drivers to cheat their tests by switching fault lights off. Every car maker has its own idea of how long the PCM needs but a few days of driving are normally enough.

Engine Compression Tests

Has your motor been running roughly or losing power? If so, there's probably a lack of pressure in the cylinders. A compression test can be done at home with a handheld compression gauge that records the pressure the piston exerts on the fuel/air mixture before the spark plugs fire. These gauges are easy to use as they either screw into the spark plug opening or are held in place. They don't cost a lot but they could diagnose a problem that won't get better on its own.

How to Learn About Cars

All car owners should know a few basics about cars so they can maintain them between services. Ask questions about how the car was fixed when your car is repaired at the garage rather than just paying the check and collecting the keys. You could also ask the mechanic to walk you through the repair if he's got time. Reading about cars and engines is another way to gain knowledge. TV documentaries will also help you understand more about how cars work. When you have built up enough confidence, try working on a car yourself. An oil change is not beyond the skills of anyone, and there are other things you can do to look after your own car like changing the battery and changing the spark plugs.