Fault Codes Explained: Current, Stored, Active, Past, & History. What’s the difference?

Fault codes, also known as Diagnostic Trouble Codes (DTCs) in professional diagnostic scanners, provide detailed information about vehicle faults, what they mean, and indicate their current and past states.

Note: The name of the DTC statuses will vary depending on the vehicle being scanned. Some cars use the codes Active and History, while other cars use Current and Stored. Both mean the same thing.

Stored and Current

Stored and Current usually points to a fault detected in the past that is still present. It’s one of the most common code statutes. You will need to address the issue so that the code status will change to STORED, at which point you can clear it.

Current Fault Codes

Current faults (Active DTCs) are codes that point to issues in your car that are currently causing problems. These codes will not clear until you fix the issue. If they do clear, they will most likely return after a day or two, unless the fault was triggered due to a glitch in the car’s system. Fix the problem, and the status of these codes will change from Current to Stored, at which point you can clear them.

Stored Fault Codes

Stored / Past / History Faults indicate issues that occurred previously but are not currently a problem. They give technicians an idea of intermittent problems or issues that might have been temporarily corrected but could return.

Event

This might not be a fault, but an event that the ECU deemed important to log. For example, an “event” could be a sudden, momentary drop in oil pressure that might warrant investigation. The fault code may say Stored and Current (Event) or Stored (Event).

MIL ON / CEL ON

MIL stands for “Malfunction Indicator Lamp,” and CEL stands for “Check Engine Light.” Both terms refer to the same dashboard warning light in most vehicles, illuminating when the vehicle’s onboard diagnostic (OBD) system detects an issue.

When someone says “MIL on” or “CEL on”, the specific fault code has triggered the check engine light or the corresponding malfunction warning in the instrument cluster.

When the MIL/CEL is on, Diagnostic Trouble Codes (DTCs) will be stored in the vehicle’s computer, which can be read with an OBD scanner to help diagnose the issue.

Can I clear stored and current codes?

When you hit “erase” on your YOUCANIC full-system scanner, here’s what typically happens:

Current/Active Faults – These will be cleared from the active list, but if the underlying issue causing the fault has not been resolved, the fault can return when you cycle the ignition back on. Think of this as turning off a check engine warning light because you have an EVAP leak. The light goes off, but if the problem persists, it will come back on.

Stored / Past / History Faults – These are cleared from the history, but if the root cause of the problem hasn’t been resolved, the fault can reappear and be logged again.

Event– Events, being more of a log than an actual fault, might not be clearable like traditional DTCs. The specifics depend on the vehicle’s diagnostic system and how it treats these events.

While you can erase or clear many fault codes from the diagnostic tool’s memory, the fault will likely return if the underlying issue that caused it hasn’t been addressed. Clearing a fault doesn’t fix the problem; it just resets the diagnostic system’s memory of that problem. Always ensure that the root cause of any fault is identified and fixed to prevent the fault code from returning.

Before clearing the codes, it’s a good practice to save the report on your scanner. Most of the time, you will not need to review stored reports, but if you are trying to troubleshoot an intermittent issue, one of the fault codes could be the Holy Grail, pointing you or your mechanic in the right direction.

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