Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Permanent Fault Codes
Permanent Fault Codes (PFCs)
PFCs are very similar to a regular Diagnostic Trouble Code (DTC), except that they cannot be reset by disconnecting the vehicle battery or cleared using a diagnostic scan tool. PFCs are DTCs that are stored in the EEPROM memory of some Electronic Control Units (ECUs) starting in 2010. Only DTCs that illuminate the Malfunction Indicator Lamp (MIL) will be stored as Permanent Fault Codes.
Starting July 1, 2019, the presence of Permanent Fault Codes will be considered in determining the vehicle's smog emission test result in states which require emission testing.
Vehicles that have a PFC stored in the OBD system will fail the smog emission test regardless of whether the MIL is illuminated because a stored PFC indicates the OBD system has not yet successfully verified that a previously detected emissions related malfunction no longer exists.
All PFCs must be cleared in order to pass state emission testing. The diagnostic scan tool can be used to check for PFCs in the "GUIDED DIAGNOSTICS" tab. The DTC number and ECU storing the DTC will be displayed for each PFC. Not all vehicles built after 2010 store Permanent Fault Codes in the ECUs, therefore if it is not applicable for the vehicle, then no PFC will be displayed in the "GUIDED DIAGNOSTICS" tab. If there are no PFCs stored in any ECU, then no additional action is required and PFCs will not be the reason for state emission testing failure. However, if there are PFCs stored, they must first be cleared to pass state emission testing.
There are only two ways that PFCs can be cleared:
- Three successful trips (no recurring faults) with the diagnostic monitor running and passing will naturally clear the MIL and PFCs.
- After the vehicle has been repaired and the DTC erased with a diagnostic scan tool or a battery disconnect, complete one successful trip with the diagnostic monitor running and passing.
It is important to note that this does not need to be done during every normal repair action. Repairing an issue and erasing the DTCs with the diagnostic scan tool will turn off the MIL after performing normal repairs and erasing the DTCs with the diagnostic scan tool. It is only necessary to check for PFCs when a repair for a DTC is done to a vehicle and that vehicle needs to pass smog emission testing.
There is one other scenario where a vehicle can pass state emission testing with a PFC present. If the vehicle completes 15 or more warm-up cycles (as defined below) and has been driven 322 kilometers (200 miles) or more since the OBD information was last cleared, the emission test will pass because the time to complete 15 warm-up cycles and drive 322 kilometers (200 miles) is reasonable for vehicles to complete the self-diagnostic tests. When the DTC fault is repaired, the diagnostic monitors and PFC diagnostics should naturally run and clear long before these limits are reached.
- One warm-up cycle is defined as: The engine coolant temperature increases a minimum of 4.4°C (40°F), a change of 22.2°C (71.9°F), and reaches at least 71.1°C (160°F) during a drive cycle.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.