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Permanent Codes

What are Vehicle Permanent Codes?

2010 and newer vehicles can fail for permanent codes.

Vehicle permanent codes, also known as Permanent Diagnostic Trouble Codes (Permanent DTCs), are codes stored in a vehicle's onboard diagnostics system (OBD-II) that indicate a persistent issue. Unlike traditional DTCs, which can be cleared by disconnecting the battery or using a scan tool, permanent codes remain stored in the vehicle's computer until the issue is properly resolved and the vehicle completes a series of diagnostic tests.

If your vehicle has 15 warm up cycles and travels 200 miles and your check engine light is not on the California smog test will not fail your vehicle for a permanent code.

Purpose and Importance

Permanent codes were introduced to prevent tampering and ensure that emissions-related repairs are adequately performed before a vehicle passes a smog check. This ensures the reliability of the repair and prevents temporary fixes that might fail soon after the inspection. Permanent codes help regulatory bodies like the California Bureau of Automotive Repair (BAR) enforce stricter emissions standards, thus contributing to better air quality.

How Permanent Codes Work

When a vehicle's OBD-II system detects an emissions-related fault, it records a temporary DTC and illuminates the Check Engine Light (CEL). If the fault persists, the code becomes a permanent DTC. To clear a permanent code, the following criteria must be met:

  1. Repair: The underlying issue causing the code must be repaired.

  2. Driving Cycle: The vehicle must undergo a series of driving conditions known as a "driving cycle." This includes starting the engine, driving at various speeds, and allowing the engine to cool down. The cycle ensures that the OBD-II system can verify the repair under different conditions.

  3. Monitors: Specific readiness monitors must complete their diagnostic checks without detecting the original fault.

Impact on Smog Check

During a smog check, the vehicle's OBD-II system is scanned for permanent codes. If any permanent codes are present, the vehicle will fail the smog check regardless of the current status of the CEL. This is because the presence of a permanent code indicates that a prior emissions-related issue was not adequately resolved.

Resolving Permanent Codes

To clear permanent codes and pass the smog check, vehicle owners should:

  1. Get a Proper Diagnosis: Use a certified technician to diagnose the exact issue causing the permanent code.

  2. Ensure Comprehensive Repair: Ensure that all related issues are fully repaired to prevent the code from reappearing.

  3. Drive to Complete the Cycle: After repairs, drive the vehicle under various conditions to complete the driving cycle. This allows the OBD-II system to verify the repair and clear the permanent code.

Benefits to Consumers and Environment

Permanent codes protect consumers from incomplete repairs and fraudulent practices by ensuring that repairs are effective and long-lasting. For the environment, this means fewer vehicles emitting harmful pollutants, leading to improved air quality and public health.


Vehicle permanent codes are a critical component of the California Smog Check Program, ensuring that emissions-related issues are thoroughly repaired before a vehicle is deemed compliant. Understanding how these codes work and the steps necessary to resolve them is essential for vehicle owners and automotive professionals alike. By adhering to these regulations, we can contribute to a cleaner, healthier environment and maintain the integrity of vehicle emissions standards.

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