$0a Permanent Diagnostic Trouble Code (PDTC)

Any confirmed DTC currently commanding the MIL On can set a Permanent Diagnostic Troubles Code (PDTC). 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). Note: This capture is from an AUTEL scan tool, which does not display MODEs using Hexadecimal symbols.

A PDTC (MODE $0a) will remain in memory after a stored DTC (MODE $03) is erased. This prevents someone from clearing a DTC before going for a state emissions test. This prevents a vehicle that would typically fail from passing. PDTCs are stored in a non-volatile RAM (NVRAM) to prevent them from being erased with the scan tool or by removing battery power from 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 must 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 (Confirmed DTC) and MODE $02 (FFD) will be cleared. The PDTC will still be in memory, but it will take only one good trip and a second key-on cycle to remove it from memory. 

If multiple PDTCs are present, clearing them from memory could take many trips and miles. If the stored MODE $03 DTC is no longer present, this should not affect driveability or emissions. Clearing a Permanent Diagnostic Trouble Code was initially complicated. Eventually, these issues were resolved by reprogramming the ECM. If a reflash update is designed to fix a PDTC issue, the PDTC will be erased during the update. If the reflash is unrelated to the PDTC, the update cannot erase it.

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 specified, each must store a SCW.

Think of an SCW as a freeze frame set in memory when a Pending DTC (MODE $07) is set for a misfire or fuel system problem. It gives the ECM the window of information it needs to monitor a recurrence under the same driving conditions. The technician cannot view this information when a Pending DTC is present. If a second failure and a confirmed DTC is set in the same window, the MIL will be ON, and a reviewable freeze frame will be stored in MODE $02. Now, the technician can review the conditions that set the DTC through the freeze frame data (FFD). 

Chrysler is the only manufacturer that provides this information through its factory scan tool. The following two captures demonstrate Similar Conditions Windows (SCW). 

For Smog Inspectors in California, pay attention to Warmup 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 counter is => 15 and the Distance Traveled is => 200 miles, the OIS will ignore the PDTC and pass this inspection portion.

For 2010MY and newer, the California Air Resources Board (CARB) created a universal drive cycle pattern for clearing misfire and fuel systems DTCs. Before this type of PDTC can be erased, Cumulative time since engine start must be 600 seconds; Cumulative vehicle operation at or above 25 miles per hour equal to 300 seconds (medium-duty vehicles with diesel engines certified on an engine dynamometer may use cumulative operation at or above 15% calculated load instead of the 25 miles per hour); and Continuous vehicle operation at idle (i.e., accelerator pedal released by driver and vehicle speed less than or equal to one mile per hour) for greater than or equal to 30 seconds. Then, the ignition must be turned off for at least five seconds and then cycled on again.

The California Smog Check Program is the only state that uses Permanent Diagnostic Trouble Codes to fail a vehicle. There are some exemptions to this rule, and they can be found at On-Board Diagnostic Test Reference - Bureau of Automotive Repair.