Why Your Car's Check Engine Light Needs a Diagnostic Machine

William Lewis

Updated Monday, April 15, 2024 at 10:59 AM CDT

Why Your Car's Check Engine Light Needs a Diagnostic Machine

Understanding the Limitations of the Check Engine Light

The car's screen could display a menu to tell you why the check engine light is on, instead of having to use a separate machine. This would provide convenience and save time for car owners. However, there are limitations to relying solely on the car's screen for diagnostic information.

Many diagnostic trouble codes (DTCs) are not always useful in determining the exact issue. For example, a P0420 code on a Honda could indicate a bad catalytic converter, bad O2 sensor, or even an exhaust leak. Even experienced mechanics may take some time to figure out the specific problem indicated by a DTC.

The check engine light serves as a signal to go see a professional because something is wrong with the car. The diagnostic machine in the garage helps the professional mechanic determine where to start looking for the problem. It provides a more comprehensive analysis of the car's systems and can identify issues that may not be apparent from the check engine light alone.

The Importance of Professional Diagnosis

The check engine light can come on due to various issues, such as exhaust gas anomalies, faulty sensors, catalytic converter problems, incomplete burning, exhaust leaks, or issues with the mass airflow sensor. If the car directly tells people what's wrong, those who don't know what they're doing may attempt to fix the problem and potentially make it worse.

People who have some knowledge about car repairs can use an OBD2 scanner to help diagnose the issue indicated by the check engine light. This low barrier to entry, such as a cheap OBD2 scanner, saves time and cost for everyone compared to having no barrier to entry. However, it is still recommended to take the car to a shop where a mechanic can manually check the wiring, sensors, and other components to determine the exact problem.

The Limitations of the Check Engine Light

The check engine light turns on when the car's computer detects an anomaly in the system, indicating that something is not sending the correct information. The computer sets a DTC, which is a guide to what happened, but it does not provide an exact explanation of the problem. It does not know exactly what caused the anomaly; it only knows that a sensor or circuit is not reading or sending the correct information.

There are numerous factors that can cause a sensor or circuit to send the wrong information, making it difficult for the computer to guess the exact issue. Instead of the computer guessing, it is recommended to take the car to a shop where a mechanic can manually check the wiring, sensors, and other components to determine the exact problem. This ensures a more accurate diagnosis and prevents unnecessary repairs.

The Role of Diagnostic Machines

Diagnostic OBD readers existed before cars had screens, so there was no need to create software or a menu for the check engine light. A $20 scan tool can provide all the necessary information about the check engine light, making a software/menu on the car's screen unnecessary. It allows car owners to access valuable diagnostic information and understand the symptoms of the issue and the general affected system.

An OBD2 readout of the check engine light provides symptoms of an issue and a general idea of the affected system, but it does not tell you exactly what is broken. For example, a code for a cylinder misfire could indicate various potential problems, such as bad spark plugs, bad ignition coils, bad wiring, bad valves, bad head gasket, bad piston rings, or a faulty crankshaft sensor. Therefore, relying solely on the check engine light or the car's screen may not provide a complete and accurate diagnosis.

While the idea of having the car's screen display diagnostic information for the check engine light may seem convenient, it is important to understand the limitations of such a system. Professional diagnosis using a diagnostic machine and the expertise of a mechanic is still crucial for accurate and comprehensive problem identification.

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