Continuous Memory Self-Test

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

There are 3 types of continuous DTCs:

• an emission-related malfunction indicator lamp (MIL) code which illuminates the CHECK ENGINE indicator in the instrument cluster.
• a non-emission related, non-MIL code which does not illuminate the CHECK ENGINE indicator, but illuminates the powertrain malfunction indicator (wrench), HAZARD, or both indicators.
• a non-emission, non-MIL code which does not illuminate any indicators.

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 1 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, the DTC that illuminates the MIL is cleared, or the keep alive memory (KAM) is reset. Also, an emission-related pending MIL and non-emission related (non-MIL) DTCs are erased after approximately 40 vehicle warm up cycles, a KAM reset, or when the DTCs are cleared.

Any scan tool that meets OBD requirements can access the continuous memory to retrieve emission-related MIL DTCs. However, not all scan 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.