Some emissions diagnostic systems support permanent diagnostic trouble codes. These are different from a fault simply returning immediately after clearing. Where supported, disconnecting the battery or using an ordinary code-clear command does not remove the permanent record; the vehicle must verify the relevant repair through its monitoring logic.
Identify the actual status
Ask for a report separating permanent codes from current, pending and confirmed records. Check whether the original symptom and warning remain. A permanent record by itself is not enough to decide that the same part needs replacing again.
Use the correct verification procedure
The required conditions depend on the vehicle and monitor. Do not follow an arbitrary internet mileage target or drive an unsafe car to make a code disappear. The workshop should consult the applicable manufacturer information and confirm that the underlying fault has been addressed.
Keep the before-and-after reports and the repair date. If the warning returns, preserve the new fault data before another reset. The California Bureau of Automotive Repair explains permanent-code behaviour; its inspection rules are specific to California and are not UK MOT guidance.
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