Mechanic workshop

What is a Car Diagnostic Test & How to DIY?

You know your car best. You drive it daily and know what it should look, sound, and smell like.

But when something goes wrong, like your check engine light comes on or you hear an unusual sound from underneath the hood, you may find your car not familiar as it should be. That's where a car diagnostic test can come in handy.

During the Covid19 pandemic, you can try to do car diagnostic tests at home by yourself when all the dealers are closed. This guide will walk you through the most common questions about the car diagnostic test and how to do it by yourself.

What is a Car Diagnostic Test?

A car diagnostic test can determine if your vehicle has issues with its engine, exhaust, transmission, ignition coils, oil tank, throttle, and more.

Car diagnostic tests are usually done in dealer shops and mechanics, while you can also do it by yourself at home. Though sounds complex, a car diagnostic test could be done in a short period of time and at a low cost by yourself.

How Often Do You Have To Do A Car Diagnostic Test?

It’s a common issue that when we only take our vehicles to the mechanics for diagnostics, we will wait until there’s a severe malfunction or breakdown, as it’s time-consuming and relatively expensive. (Question, have you ever ignored a check engine light until it’s time for an inspection?)

If you learned about how to do a simple diagnostic test on a car by yourself, you can do it regularly and prevent severe problems from happening, as you can see minor issues and fix it with simple repairs long before it’s become a major problem and cost hundreds or even thousands. It’s definitely a more efficient and cost-effective approach than taking your vehicle to the mechanic till it’s broken down.

What is a Car Diagnostic Test?

A car diagnostic test can determine if your vehicle has issues with its engine, exhaust, transmission, ignition coils, oil tank, throttle, and more.

Car diagnostic tests are usually done in dealer shops and mechanics, while you can also do it by yourself at home. Though sounds complex, a car diagnostic test could be done in a short period of time and at a low cost by yourself.

How Often Do You Have To Do A Car Diagnostic Test?

It’s a common issue that when we only take our vehicles to the mechanics for diagnostics, we will wait until there’s a severe malfunction or breakdown, as it’s time-consuming and relatively expensive. (Question, have you ever ignored a check engine light until it’s time for an inspection?)

If you learned about how to do a simple diagnostic test on a car by yourself, you can do it regularly and prevent severe problems from happening, as you can see minor issues and fix it with simple repairs long before it’s become a major problem and cost hundreds or even thousands. It’s definitely a more efficient and cost-effective approach than taking your vehicle to the mechanic till it’s broken down.


How Long Does a Car Diagnostic Test Take?

A normal car diagnostic test should only take a few minutes to complete. Every car diagnostic test starts with check engine light code reading, AKA OBD2 Codes reading, and this will only take several minutes. The mechanics will plug in a car diagnostic scanner to read the trouble codes which indicates where the problem is.

After pulling the Diagnostic Trouble Codes, the mechanics will then do some investigative work to get a more accurate picture of what is functioning incorrectly and how best to fix it depending on the error codes that appeared.

If you decide to take your vehicle to an auto shop, you should be prepared to wait a little bit before the test and stay afterward to discuss what issues were found and how they can be resolved. I’d say you should expect to spend at least an hour for any car diagnostic test, and 2-3 hours could be a reasonable estimate.

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Clicking or Tapping Noise from Engine

Engines can produce a lot of noises, but a metallic tapping or clicking sound means your engine may be low on oil, or is not developing normal oil pressure. The clicking noise is coming from the valve train. If oil pressure is low because of a low oil level in the crankcase or a problem with the oil pump, the hydraulic lifters that open and close the valves may collapse creating an increase in valve lash. This is the noise you hear, and it will be coming from the vicinity of the valve covers on top of the engine.
Stop the engine, let it sit a few minutes (so the oil can run back down into the crankcase), then check the oil level on the dipstick. If low, add oil as needed to bring the level back up to the full mark. Do not overfill the crankcase with oil. Also, check the engine for oil leaks. Old valve cover and pan gaskets, or leaky crankshaft end seals can allow oil to leak out of the engine.

If the noise does not go away, and/or the oil pressure gauge or warning light indicates low oil pressure, it's not a good idea to keep driving your vehicle. Loss of oil pressure can cause extensive and expensive engine damage.

Other engine sounds can also mean bad news. A deep metallic rapping noise can be caused by worn connecting rod bearings, and may indicate your engine has reached the end of the road (or will soon!).

If you hear a metallic knocking or clattering noise that only occurs while accelerating or when driving up a steep hill or pulling a load, your engine is likely experiencing detonation, a potentially damaging form of erratic combustion. Detonation can be caused by a buildup of carbon in the combustion chambers, low octane fuel, engine overheating, an EGR system that is not working, over-advanced ignition timing, or a defective knock sensor.