Inspection/Maintenance Test DTCs, commonly referred to as Permanent DTCs, are codes that are currently commanding on the Check Engine MIL (Malfunction Indicator Lamp) and are stored in non-volatile memory of an electronic control module. (Fig. 3) These DTCs, which first appeared on 2010 GM models and have been required on all 2012 and later GM models, cannot be cleared using a scan tool or by disconnecting power to the control module, making them “permanent” codes.
Fig 3
The DTC data is intended to prevent vehicles from passing Inspection/Maintenance (I/M) inspections required by some states/provinces and local governments in order to renew license plates if there is an emissions-related condition. Since the permanent codes cannot be cleared by disconnecting the battery or using a scan tool, the presence of these fault codes at an inspection without the MIL illuminated indicates that the proper repairs were not verified by the on-board diagnostic (OBD II) system. A vehicle will only pass an inspection by using a scan tool to confirm that no Permanent DTCs are present.
Any DTC that illuminates the MIL can be a Permanent DTC, including DTCs set by control modules other than the ECM.
New Naming in SI and GDS 2
In the past, there may have been misperceptions by some technicians regarding the naming of I/M Test DTCs and Permanent DTCs. These terms are interchangeable. The most common use in dealerships appears to be “Permanent” DTC, while the term Inspection/Maintenance Test DTC is used in the Service Information and GDS 2.
As a result, the naming of the I/M Test DTCs is being changed to Permanent DTCs in both the Service Information and GDS 2. All I/M Test DTCs references will now be listed as Permanent DTCs.
Clearing Permanent DTCs
Permanent DTCs will be cleared by the OBD II system when the internal algorithm for the DTC passes and the MIL is no longer being commanded on. The Permanent DTC will clear from the control module after the ignition has been turned off (power down).
– Thanks to Chris Henley and Morgan Chemello
