Understanding the warning lights displayed on the dashboard

Vehicles are largely divided into engine, chassis, body, computer system. There is an electronic control unit (ECU) computer for each area. If input from sensor is out of the range specified for each sensor, the corresponding ECU displays a warning light. Below is an article on the engine side. It is also different for each diagnostic device and vehicle. So, please understand the following as a general case.​

Why is the engine warning light on and what does it mean?

Numerous parts such as fuel, air, electricity, ignition, cylinder, injector, air sensor, pressure sensor, and temperature sensor make up the engine. We don't know exactly which of these is faulty. The computer that controls the engine (ECM, Engine Control Module) obtains information from various sensors. And if sensor input is out of the preset range, the engine warning light (CEL, Check engine light) is displayed. What does engine warning light mean? That means that ECM left a fault code (DTC, Diagnostic trouble code). So, scanning it with a diagnostic machine and repair the issue if at all. That’s what it means.​

No one can know for sure what the fault is until the fault code (DTC) is checked with a scanner.

So, the best thing to do is to post the DTC if you ever ask a question on a forum. Then it will b easier to diagnose and analyze the issue. It can also prevent unnecessary over-maintenance. Of course, you can also save time and headache as well. OBD2 for about US$7.00 and a scanner program (eg Torque pro) for less than US$10.00 are good enough for most of DIY requirements.

3 cups of coffee, OBD2 scanner is enough to diagnose most engines

OBD2 is a diagnostic device that must be installed as onboard diagnostics. 1969 VW first introduced onboard diagnostics system. From 1996, OBD2 has been compulsory for all vehicles sold in the United States. The biggest reason was exhaust gas regulation for environmental protection. Afterwards, the chipsets became widespread as they were mass-produced. The basic functions are the same for both the expert's several thousand US dollars diagnostic device and the less than U$10.000 OBD2. So, why not just invest the price of 3 cups of coffee to prepare an OBD2 scanner and program.

​OBD2 scanner basic knowledge & minimal training is enough

Basically, in the case of Korea, I understand that OBD2 was introduced in the mid-2000s. It may be different for each vehicle, so you need to check if there is OBD2. Also, it is possible to check and delete the fault code with the OBD2 program. Therefore, users can directly scan the fault code (DTC) and, if necessary, delete the DTC and watch the progress.

​Understanding the basic structure of DTC

In OBD2, it is broadly classified as follows. A typical DTC looks like P0301 format. Take a look at the sample below using P0301. P0301 is the fault code for cylinder 1 misfire. Let's take a closer look.

​The first alphabetic meaning of DTC. In case of P0301, it means there is a problem with the engine side.

P - Engine. Powertrain, transmission, etc. (common)
C - Chassis. Suspension, handling, brakes, etc. (often)
B - Body. In-vehicle issues (rare)
U - Electric. Battlefield. computer systems, etc. (rare)

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The meaning of the number in the second line. The second among P0301 is 0. Therefore, it is a global or generic code.

0 – Universal code, meaning the code supported by all vehicles according to the OBD2 standard. This is supported by all OBD2 scanners.
1 - Manufacturer-specific code. It means a unique code used by each manufacturer. This is supported by high-priced scanner, but some low-cost devices also support a limited number of manufacturers.

​3rd digit meaning. The third among P0301 is 3. That is, injectors, fuel. This is an air-side fault code.

1 – Fuel and air volume measurement
2 – Injector circuit fuel and air volume measurement
3 – Ignition system or misfire
4 – Additional exhaust gas management
5 – Vehicle speed control, idle control, etc.
6 – Computer and I/O electric circuit system
7 – Transmission

The meaning of the 4th and 5th numbers.

The last two digits of 01 in P0301 means cylinder 1 in engine, general purpose, and true story. If the DTC is P0302, it is cylinder 2, and if it is P0306, it means cylinder 6 of the 6-cylinder engine is misfired.01. Ignition system for DTC P0301. It means the first true story.

0 to 99 - are used, and this is a very specific issue code.

In addition, there are more than 11,000 DTC codes out there. So, for generic issues affordable OBD2 is good enough, for full system diagnostics then professional scanner is recommended.
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