Permanent code (PDTC)
Definition
A permanent DTC is an emission-related confirmed code that the ECU keeps in a protected Mode 0A memory and that cannot be erased with a scan tool, by disconnecting the battery or by any reset procedure; it was introduced on 2010 and later vehicles to stop people clearing codes just before an emissions inspection. The only way to remove it is to fix the fault and let the ECU re-run the relevant monitor and pass it, which normally requires a complete drive cycle under the right conditions; some ECUs need the monitor to pass on two trips. Inspection programmes in several regions will fail a car with a permanent code even when the MIL is off and the stored code has been cleared. On the shop floor it is a useful reality check: if a permanent code is still present after a repair, the monitor has not yet passed, either because the drive cycle was not completed or because the repair did not work. Typical permanent codes are P0420/P0430, P0171/P0174, P0300-P0304 and the EVAP leak codes P0442/P0455/P0456.
Codes often stored
- P0171System Too Lean (Bank 1)
- P0300Random / Multiple Cylinder Misfire Detected
- P0420Catalyst System Efficiency Below Threshold (Bank 1)
- P0430Catalyst System Efficiency Below Threshold (Bank 2)
- P0442Evaporative Emission System Leak Detected (Small Leak)
- P0455Evaporative Emission System Leak Detected (Gross Leak)