Continuous Memory Self-Test

Testing for Continuous Memory DTCs is a functional test of the powertrain control module performed 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 at the time of testing for Continuous DTCs and is therefore, especially valuable when diagnosing intermittent faults. This test will detect failures contributing to driveability or emission concerns. The vehicle may need to be driven or the OBDII Drive Cycle completed to allow the PCM to detect a fault. Refer to DRIVE CYCLES  . When a fault is stored in memory, a Diagnostic Trouble Code (DTC) will be output on the data link at the end of the test when requested by a scan 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 nonemission-related non-MIL code which will never illuminate the cluster indicator.

For emission-related MIL codes, the PCM will store the DTC in continuous memory when a fault is detected for the first time. At this point the DTC will 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 star-run cycle, the emission-related MIL code will illuminate the MIL. The MIL will remain on even if the fault is intermittent. The MIL will be extinguished if the fault is not present through three consecutive drive cycles or a PCM reset is performed. Also, an emission-related pending MIL and nonemission-related non-MIL code will be erased after approximately 40-80 vehicle warm up cycles or a PCM reset.

Any scan tool that meets OBDII requirements can access Continuous Memory to retrieve emission-related MIL DTCs. However, not all scan tools access pending and nonemission-related non-MIL DTCs in the same way. If using the New Generation Star (NGS) scan tool, all MIL (including pending) and non-MIL codes are retrieved together on the same screen. During most diagnostic procedures in this manual, it is required that all DTCs be retrieved and cleared. Consult the instruction manual from the tool manufacturer for specific instructions.