Understanding Check Engine Light Codes and Their Permanent Removal

Recently, a user asked whether a check engine light code can be permanently deleted without deleting other codes. After purchasing a used car from an individual, the check engine light activated 2 days later, which raises several important questions about fault codes, their permanence, and effectively dealing with them.

Understanding Fault Codes and Their Criteria

Before we dive into the specifics, it's essential to understand that fault codes serve as a diagnostic starting point. They are diagnostic trouble codes (DTCs) that identify a test failure in a vehicle's computer system. The only true way to permanently delete a fault code is to rewrite the software routines in the control module used to run the test. Simply clearing codes with a scan tool or disconnecting the battery does not truly delete anything but rather resets the system to report new issues.

The Criteria for Setting Fault Codes

Different fault codes have varied criteria for setting and different conditions under which they are tested. Some test failures may be detected immediately upon turning the ignition, while others require multiple test failures under specific driving conditions to trigger the check engine light. Understanding the criteria for setting these codes is crucial in determining why the light communicates with the user.

A Scenario and Its Possible Explanations

The user in the scenario mentioned that the used car had other minor codes before the purchase. The question here is whether and how these minor codes could have been cleared, leading to the check engine light not illuminating immediately. The possibility exists that some minor codes may not have triggered the light until the system determined there were two or more failures. Alternatively, the described 'minor codes' could have been incomplete OBDII monitor tests. To provide a more specific answer, the exact code numbers, vehicle's year, make, and model would be necessary.

Temporary Clearing Methods

Disconnecting the battery briefly is one method to clear fault codes, albeit temporarily. By disconnecting the battery for a few minutes, the ECU (Engine Control Unit) loses its memory, including the fault codes. However, this does not resolve the underlying issue, and the light may come back on once the system relearns the conditions. Therefore, fixing the underlying fault is always the most effective solution.

When to Address the Fault

It is generally not advisable to purchase a vehicle with a check engine light on, as it indicates a potential issue that needs to be diagnosed. A scan tool can help determine the extent of the problem. Disregarding a malfunction can lead to further damage, such as an engine rebuild, which can cost significantly more than the cost of fixing the initial issue.

Passing a Smog Test

If the primary goal is to pass a smog test for vehicle registration, there are temporary solutions, such as battery reset followed by a series of steps to allow the system to stabilize. Here's a simple procedure:

Disconnect the battery for 30 minutes to clear the the battery and allow the system to idle for 20 minutes.Take the car for a normal drive.

While these steps can mask the issue temporarily, they do not address the root cause. In the long run, it's crucial to repair the fault that caused the check engine light to come on in the first place.

Conclusion

In conclusion, while there are temporary methods to clear the check engine light codes, such as a battery reset, these do not offer a permanent solution. The best approach is to identify and solve the underlying issue causing the fault. If you're looking for a quick fix to pass a smog test, a battery reset followed by a stabilized driving session can be a temporary workaround, but always consider the long-term health of your vehicle.