Continuous Memory Self-Test

The continuous memory self-test is a functional test of the PCM carried out under any condition (engine running or off) with the key on. Unlike the KOEO and KOER self-tests, which can only be activated on-demand, the continuous self-test is always active. A fault does not need to be present when accessing continuous memory self-test DTCs, making the test valuable when diagnosing intermittent faults. The vehicle may need to be driven or the on-board diagnostic (OBD) drive cycle completed to allow the PCM to detect a fault. Refer to ON BOARD DIAGNOSTIC (OBD) DRIVE CYCLE  for more information. When a fault is stored in memory, a DTC will be output on the data link at the end of the test when requested by a diagnostic tool.

There are two types of continuous DTCs. The first type is an emission-related malfunction indicator lamp (MIL) code which will illuminate the CHECK ENGINE or SERVICE ENGINE SOON indicator in the instrument cluster. The second is a non-emission related, non-MIL code which will not illuminate the cluster indicator.

For emission-related MIL codes, the PCM stores the DTC in continuous memory when a fault is detected for the first time. At this point the DTC does not illuminate the MIL and is now considered a pending code. The purpose of pending codes is to assist in repair verification by reporting a pending DTC after one drive cycle. If the same fault is detected after the next ignition start-run cycle, the emission-related MIL code illuminates the MIL. The MIL remains on even if the fault is intermittent. The MIL is extinguished if the fault is not present through 3 consecutive drive cycles or the DTCs are cleared. Also, an emission-related pending MIL and non-emission related (non-MIL) DTCs are erased after approximately 40 vehicle warm up cycles or the DTCs are cleared.

Any diagnostic tool that meets OBD requirements can access the continuous memory to retrieve emission-related MIL DTCs. However, not all diagnostic tools access pending and non-emission related (non-MIL) DTCs in the same way.

During most diagnostic procedures in this article, it is required that all DTCs be retrieved and cleared. Consult the instruction manual from the tool manufacturer for specific instructions.