Pending, Stored, and Permanent Codes | What They Mean in Car Scanner

When using auto scanner, you'll encounter three different forms of diagnostic codes: Pending Codes, Stored Codes, and Permanent Codes.

Each of these codes plays a unique role in diagnosing engine performance and emissions issues.

In the following article, we will provide a comprehensive explanation of each type of code, including their characteristics, applications, and how to address them effectively.

What Are Pending Codes

Pending Codes are Diagnostic Trouble Codes (DTCs) that the vehicle's onboard diagnostic system (OBD) has detected but has not yet confirmed. These codes signify that an issue exists but has not reached the threshold to trigger a check engine light.

• Temporary Nature: Pending Codes are temporary indicators of an issue, signaling that a fault has been detected but requires further monitoring.

• Recent Detection: These codes often emerge after a recent event, such as a failed emission test or irregular sensor readings.

• Monitoring Requirement: The OBD system must observe the fault under specific conditions multiple times before it can escalate to a Stored Code.

Examples of Pending Codes

1. Oxygen Sensor Issues (DTC P0131): If an oxygen sensor exhibits fluctuating readings, it may generate a Pending Code like P0131, indicating that the sensor is reading low voltage. The system will continue to monitor the sensor to confirm the fault.

2. EVAP System Faults (DTC P0455): A large leak detected in the evaporative emissions control system could trigger a Pending Code P0455. This indicates a problem that requires further observation during subsequent driving cycles.

3. Mass Airflow Sensor Problems (DTC P0101): If the mass airflow sensor provides inconsistent readings, it may trigger a Pending Code P0101. The vehicle’s system will need to monitor this sensor to determine if the issue persists.

Related Reading: How to Clear Permanent Engine Codes?

What Are Stored Codes

Stored Codes are DTCs that have been confirmed as persistent issues. These codes indicate that a fault has been detected consistently and has met the criteria necessary to illuminate the check engine light.

• Confirmed Issues: Unlike Pending Codes, Stored Codes represent faults that have been verified by the OBD system over multiple monitoring cycles.

• Check Engine Light Activation: When a code becomes stored, it typically triggers the check engine light, alerting the driver to the issue.

• Resetting Monitors: After repairs, stored codes can be cleared, but the vehicle’s monitors must be reset to ensure proper functioning of emissions-related systems.

Examples of Stored Codes

1. Catalytic Converter Efficiency (DTC P0420): A Stored Code like P0420 indicates that the catalytic converter is not functioning efficiently. This often requires inspection or replacement of the converter.

2. Oxygen Sensor Slow Response (DTC P0138): If an oxygen sensor is detected to be slow in its response, a Stored Code P0138 may appear. This indicates the need for diagnostic checks on the sensor and its circuit.

3. Fuel System Rich Condition (DTC P0172): A Stored Code P0172 signifies that the fuel system is running too rich. This can lead to poor fuel economy and potential engine damage if not addressed.

What Are Permanent Codes

Permanent Codes are unique in that they indicate a fault that has been detected and verified but cannot be cleared using standard methods. These codes remain in the system until the underlying issue is resolved and can only be reset through specific procedures.

• Non-Clearable: Permanent Codes cannot be erased by simply using a scan tool or disconnecting the battery. They persist in the system to ensure that unresolved issues are addressed.

• Post-Repair Monitoring: After repairs, the vehicle must meet specific conditions for the monitors to reset and clear the Permanent Code.

• Emissions Compliance: These codes are particularly important in emissions testing, as they indicate unresolved issues that can lead to failure in inspections.

Application Examples of Permanent Codes

1. Oxygen Sensor Malfunction (DTC P0133): A Permanent Code like P0133 indicates a persistent issue with an oxygen sensor that has not been resolved. Until the sensor is repaired or replaced, this code will remain.

2. Evaporative Emission Control System (DTC P0442): A Permanent Code P0442 signifies a small leak in the EVAP system that remains unresolved. The vehicle will need to undergo diagnostic checks to find and fix the leak.

3. Catalytic Converter Damage (DTC P0421): This Permanent Code indicates a failure in the catalytic converter's efficiency. The vehicle must be repaired before the code can be cleared.

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Can These Codes Be Cleared

Clearing Pending and Stored Codes

Both Pending Codes and Stored Codes can typically be cleared using an OBD-II scanner. These tools could be used to read and reset diagnostic trouble codes effectively. 

Using  OBD2 Scanners

To clear codes, simply connect the ANCEL V6 Pro OBD2 scanner to the vehicle's diagnostic port, usually located under the dashboard.

After powering on the scanner and navigating to the codes section, you can select the option to clear or erase codes.

This action sends a command to the vehicle’s computer, resetting the codes.

It’s important to note that clearing codes does not fix the underlying issue; it merely removes the indication of a fault.

To fully resolve the problem, you need to identify and repair the root cause of the issue.

This involves diagnosing the specific component that triggered the code, fixing or replacing it, and then verifying that the repair was successful.

Only after addressing the underlying problem will the codes stay cleared and the vehicle operate correctly.

Disconnecting the Battery

An alternative method to clear codes is to disconnect the vehicle’s negative battery terminal.

This action cuts power to the onboard computer, resetting it and clearing both Pending and Stored Codes.

However, this method can have drawbacks. While it may clear codes, it can also reset other vehicle settings, such as the clock and radio presets.

Additionally, not all vehicle monitors may reset, leading to potential issues when attempting emissions testing.

Post-Clearing Procedures

After codes are cleared, the vehicle often needs to be driven for a specific number of cycles to ensure that all systems are ready for emissions testing.

This is because the onboard diagnostic system must recheck all monitored components, such as the EVAP system and oxygen sensors, to confirm they are functioning correctly.

The number of cycles required can vary by vehicle make and model, so consulting the owner’s manual or a repair guide is advisable.

Monitoring System Readiness

After clearing codes and completing the necessary driving cycles, it’s essential to check the vehicle's readiness monitors using the OBD-II scanner. This step verifies that all systems are functioning correctly and are ready for emissions testing. If the monitors indicate any issues, further diagnosis may be necessary before the vehicle can pass inspection.

Managing Permanent Codes

Managing Permanent Codes requires a more nuanced approach compared to Pending and Stored Codes.

Unlike those codes, Permanent Codes cannot be cleared using a standard OBD2 scanner or by simply disconnecting the battery.

Fixing the Underlying Issue: The first step in managing a Permanent Code is to identify and fix the underlying problem.

If a Permanent Code related to an oxygen sensor (like P0138) appears, it indicates that the sensor or its circuit is malfunctioning.

Technicians must diagnose and repair the root cause, which may involve replacing faulty sensors, repairing wiring issues, or addressing exhaust leaks.

Performing Diagnostic Tests: Once the issue is resolved, the vehicle’s onboard system must perform specific diagnostic tests to reset the Permanent Code. These tests include:

• Monitor Readiness Tests: The OBD system checks various components, such as the fuel system and oxygen sensors, to ensure they function correctly under predefined conditions.

• Continuous Monitoring: Components like oxygen sensors are continuously monitored during engine operation. The vehicle must be driven under various conditions (idle, acceleration, deceleration) to confirm consistent readings.
• Key-On Engine-Off (KOEO) Tests: These tests check the functionality of components without the engine running, verifying that sensors and circuits are operational.
• Key-On Engine-Running (KOER) Tests: Conducted while the engine runs, these tests evaluate performance for components like fuel injectors and ignition systems.
• Self-Diagnostic Procedures: Many vehicles run built-in self-diagnostic routines that perform checks when the vehicle starts, helping to identify any persistent issues.
• Emission System Checks: For emissions-related codes, the system verifies components like catalytic converters and EVAP systems to ensure they meet operational standards. This may require specific driving conditions over a certain distance or number of cycles.

Driving Conditions for Monitors: After repairs, it’s crucial to drive the vehicle under specified conditions to allow the OBD system to complete its checks.

This typically means driving for a specific distance or duration, incorporating various driving scenarios such as idle, acceleration, and highway speeds.

Each vehicle has its own requirements, and following these ensures that the monitors can validate that the repair was successful.

Code Reset Confirmation: After the diagnostic tests, if the system determines that the repairs were effective, the Permanent Code will eventually reset on its own. However, it may take several drive cycles for this to occur, and the check engine light will typically remain illuminated until all necessary monitors are ready and confirmed by the system.

Conclusion

Pending Codes, Stored Codes, and Permanent Codes are crucial for effective vehicle diagnostics.

Each type provides valuable information about your car's performance and emissions. If you're seeking reliable diagnostic tools, consider Ancel's range of OBD-II scanners.

Their user-friendly features make it easy to identify and resolve issues in your vehicle, ensuring it stays in top shape.

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