How to Diagnose Car Problems

In the past, most drivers knew a thing or two about cars. And they had to – car service shops were few and far between. On top of that, the vehicles of the time were easier to maintain – no electronics to care about. Today, the opposite is true – car service shops are everywhere, and the vehicles are full of technology. But, should that detract you from learning how to diagnose car problems? Of course not! Diagnosing your car yourself is cheaper and more convenient, especially when you’re on the road.

check engine light meaning

The thing is, you can’t just stop your vehicle, check the engine bay and boom, you found the problem. Modern vehicles can be very complicated, and some issues won’t show in the driving experience. Your car will drive just fine, yet there can still be a faulty unit somewhere. Usually, modern cars will signal the error via a light on the instrument panel (i.e., the “check engine” light). Then, where to go from there?

In this article, I will show you how to diagnose car problems. I’ll start with the usual mechanical issues, and then I will cover the electronic stuff, like sensors, for example.

Use Your Senses for Mechanical Issues

Unlike errors with the electronics, most mechanical issues can be felt by your senses. The most obvious one is looking for them. For example, if there’s an oil leak, you can see a puddle below the engine when the car is stationary. You can use this for other fluids, like brake fluid (translucent and oily) or engine coolant (green or orange). Either way, when you see that something’s dripping below your car, you should immediately react. You certainly don’t want your brakes to stop working while driving, do you?

engine oil leak

Then, you can also use your ears for strange noises. Most of the time, you can locate where the sounds come from, like the engine bay or the suspension.

Here are the most common mechanical problems you can hear while driving:

  • Suspension Components: If the shock absorbers are worn-out, they usually emit a clunking noise when you hit a larger pothole. Other suspension components like bushings and ball joints can produce a creaking sound, while joints can produce ticking sound. Problems with the suspension can cause uneven wear on the tires, too.

uneven tire wear

  • Engine Components: The most common noise is squealing, and it usually comes from a loose timing belt. That said, the same noise can come from the serpentine belt, so it’s best to check in the engine bay. If you hear loud popping from the engine bay, it seems like you have some problem with the ignition. Usually, it is a spark plug, but it can also mean that one of the injectors doesn’t work correctly.
  • Brake Components: Worn-out brake pads squeal and grind. When you hear that noise, you can visually check how much they’re worn out. If there’s no material left on them, replace them immediately!

worn brake pads

Other than hearing for noises, you can also feel if your car behaves strangely while driving. For example, if your car leans to one side, one of your tires may be deflated. You might also need to balance the tires or align the wheels if there’s a vibration at higher speeds. That said, both leaning and vibrations can mean problems with the suspension.

How to Diagnose Your Car for Other Issues?

It seems that modern cars have more problems with faulty sensors or other electronic components than with the mechanics. According to most reliability surveys, that’s entirely true – advanced automotive systems are often the first to fail. Luckily, when that happens, you will see a warning light on the instrument panel. Usually, the “check engine” light appears, but you might also see a high-temperature warning and low oil pressure warning. If the latter two appear, check the coolant level (on the reservoir) or the oil level (via the dipstick). If the “check engine” light appears, things aren’t as straightforward.

Using A Car Problem Diagnosis Tool

All car services use tools that support the OBD-II (On-Board Diagnostics) standard to diagnose car problems. These systems check the DTC memory inside the vehicle, which contains information on the error that one of the components has. Most mechanics use a laptop connected to the OBD-II port to see which error shows on the screen. Thanks to the system, they can diagnose the problem quickly and efficiently, or in around 10-20 minutes.

engine computer diagnosis

However, diagnosing your car at a mechanic can be costly, which is why you should probably do it yourself. Car diagnostics tools can be had for $20 for simple code readers and up to a few hundred dollars for professional options. There are even some Bluetooth options that connect to your phone! Which one you need is really up to you, but for most errors, even the cheapest tools will work just fine.

Please note that older vehicles, before 1996, used the non-standardized OBD-I standard. If you own one of those vehicles, you will need a tool that can connect to your particular car. In other words, you will need a diagnostic tool for your make, model, and year of production.

Car Diagnosis Process

You can diagnose car problems with the OBD-II diagnostics tool if you own a vehicle produced after 1996. Here are all the steps needed to analyze your car thoroughly when the “check engine” light appears:

  • Turn the ignition of the vehicle off. The diagnostics tool can’t work if your vehicle is “ON” or ignited.

obd-ii diagnosis port

  • Find the OBD-II plug in your vehicle. In most modern vehicles, the diagnostics connector is located on the lower side of the dashboard, left to the steering wheel. However, some models have the plug located on the center console. If you can’t find the connector, a quick Google search can help. You can also find the same information in the owners’ manual.
  • Smoothly insert the plug into the connector. Make sure that you position the plug correctly.
  • Enter the make, model and year of production, or the VIN of your car. Some diagnostics tools will be able to obtain the type of vehicle automatically.

engine diagnosis results

  • Wait until the tool communicates with the vehicle’s DTC memory and shows you the error code. Write it down so you can research it thoroughly.
  • After you’ve repaired the problematic part, delete the error code from the DTC memory. Otherwise, the “check engine” light will still appear, and you’ll not know if the problem was fixed.

What Does A Diagnostic Test Show On A Car?

The diagnostic test will show you an error code that it reads from the DTC memory. Search online for what the error code means. Usually, you can find information on errors on the most popular search engines, as well as some tips for repair. Some forums have surprisingly detailed guides on how to pinpoint the problem.

For example, the P062D error code means that there’s a problem with the fuel injector driver circuit for engine bank one. Usually, this means that the fuel injector isn’t functioning correctly and should be immediately repaired or replaced.

Some more advanced diagnostic tools can also show you additional error information while the car is running. These tools will show you real-time data as opposed to stored errors in the DTC memory. You can use this method to see detailed parameters of the problematic injector in real-time.

Car Diagnostic Cost

If you want to analyze your car by yourself, you only pay for purchasing the diagnostic tool. However, if you trust your mechanic to diagnose the car, the cost will be much higher. Depending on the vehicle and the car service, the price for diagnosing can range from $20 to over $100. That said, an experienced mechanic might find additional issues with your car that will not show on the OBD-II tool.

How Long Does it Take A Mechanic to Diagnose A Car?

It depends on the diagnostics you paid for. For a quick check on the error code, the mechanic may need 30 minutes, but full-on diagnostics may take hours. When a mechanic can diagnose car problems thoroughly, he/she may need to drive it while checking the parameters on a laptop.

Check engine light on? Diagnose it with this easy-to-use tool.


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