A Permanent Diagnostic Troubles Code (PDTC) can be set by any confirmed DTC currently commanding the MIL On. They first appeared in 2010 as part of a three-year phase-in period. By the 2012 model year, all vehicles could set a PDTC. The ECM must have enough memory to store a minimum of four permanent DTCs.
The following capture is an example of the three possible DTCs: a Pending DTC (MODE $07), a stored DTC (MODE $03), and a Permanent Diagnostic Trouble Code (MODE $0a).
A PDTC is designed to prevent a stored DTC (MODE $03) from being erased before going in for a state emissions test. This prevents a vehicle that would typically fail from passing. PDTCs are stored in non-volatile ram (NVRAM) to prevent them from being erased with the scan tool or by removing battery power to the ECM.
A PDTC can only be erased from memory if the OBD system extinguishes the MIL (e.g., when the current DTC changes to a History DTC). If the memory is not cleared with a scan tool, the ECM will need to see the related monitor test complete and pass on three consecutive trips. The PDTC will not be removed from memory until the fourth key-on cycle. If the memory is cleared with the scan tool, the MIL will be extinguished; the MODE $03 DTC and MODE $02 Freeze Frame Data will be cleared. The PDTC will still be in memory, but it will take only one good trip to remove it from memory.
If multiple PDTCs are present, it could take many trips and miles to clear them from memory. This should not affect driveability or emissions if the stored MODE $03 DTC is no longer present. Initially, there were many issues with clearing a Permanent Diagnostic Trouble Code. Eventually, these issues were resolved by reprogramming the ECM.
For a Misfire and Fuel System PDTC, the ECM must support storing up to four similar conditions window (SCW) in NVRAM to allow proper clearing from memory. If a Misfire of Fuel System PDTC is stored during the first occurrence, the ECM must store an SCW that includes: engine speed +/- 375 rpm, engine load +/-20 %, and the same warmup condition below 160°F or 160°F and above. The SCW allows the ECM to monitor the specific Misfire/Fuel system conditions when the DTC was initially set. If additional Misfire or Fuel System DTCs are set, each must store a SCW.
Chrysler is the only manufacturer to provide this information through their factory scan tool. This is demonstrated in the following two Similar Conditions Windows captures.
For Smog Inspectors in California, pay attention to Warm up cycles and Miles Driven. PID $30 (Warm Up Cycles Since Cleared) and PID $31 (Distance Traveled Since Cleared) are used by the OIS to Pass or Fail a vehicle with a PDTC(s). If the Warm-Up Cycles are 14 or less or the Distance Traveled is less than 200 miles, the OIS will fail the vehicle. If the Warm-Up Cycle is => 15 and the Distance Traveled is => 200 miles, the OIS will pass the PDTC status.