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 ignition ON. Unlike the KOEO and KOER self-tests, which can only be activated on demand, the continuous memory self-test is always active. A concern does not need to be present when accessing continuous memory self-test DTCs, making the test valuable when diagnosing intermittent concerns. The vehicle may need to be driven or the OBD drive cycle completed to allow the PCM to detect a concern. Refer to On Board Diagnostic (OBD) Drive Cycle  for more information. When a concern is stored in memory, a DTC is output on the data link when requested by the scan tool.

There are two types of continuous DTCs. The first type is an emission related code which illuminates the malfunction indicator lamp (MIL) in the instrument cluster. The second is a non emission related, non-MIL DTC which does not illuminate the instrument cluster indicator.

For emission related MIL DTCs, the PCM stores the DTC in continuous memory when a concern is detected for the first time. At this point the DTC does not illuminate the MIL and is 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 concern is detected after the next drive cycle, the emission related MIL DTC illuminates the MIL and sets both a confirmed MIL DTC and a permanent DTC. The MIL remains illuminated even if the concern is intermittent. A permanent DTC is stored until three consecutive passing drive cycles have been completed after a repair and the MIL turns off, or after a request to clear DTCs has been made using the scan tool and the next monitoring cycle has completed and passed for that DTC.

Confirmed emission related MIL DTCs and any non-emission related, non-MIL DTCs are erased approximately 40 vehicle warm-up cycles after the concern was last detected, or if the DTCs are cleared by the scan tool.

Pending emission related MIL DTCs that never detect a concern on a second consecutive drive cycle (and never illuminate the MIL) are not stored in memory for any number of vehicle warm-up cycles; they are immediately cleared when the next monitoring cycle has completed and passed for that DTC, or until a request to clear DTCs has been made by the scan tool.

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. Permanent DTCs cannot be directly cleared by the scan tool. When a scan tool clears DTCs, pending and confirmed DTCs are immediately cleared. Permanent DTCs will not clear until the next monitoring cycle has completed and passed for that DTC. For additional information, refer to Powertrain Control Software, Permanent Diagnostic Trouble Code (DTC).