Continuous Memory DTC Access: Overview

PURPOSE
This mode is to enable the scan tool to obtain stored Diagnostic Trouble Codes (DTCs). All scan tools (NGS and generic) are capable of obtaining, converting and displaying OBD II emission related DTCs (MIL DTCs) from a vehicle. These DTCs are transmitted in response to an OBD II Mode O3 request. The DTC, descriptive text or both will be displayed. Specific menu access to emission related DTCs (MIL only) is determined by the scan tool manufacturer.

DESCRIPTION
Continuous Memory DTC access is a self-test of the powertrain control system. The Continuous Self-Test is always active, unlike the KOEO and KOER self-tests, that can only be activated On-demand. The test consists of all the OBD II monitors, and the Comprehensive Component Monitor. It is designed to detect failures contributing to driveability or emission concerns. When this test detects a fault, a Diagnostic Trouble Code (DTC) will be stored in PCM memory. The DTC can be retrieved at a later time even if the fault no longer exists. This capability makes Continuous Self-Test valuable when diagnosing intermittent faults.

As part of Quick Test, the technician retrieves DTCs that have been stored in Continuous Memory. During pinpoint testing, the technician may perform a specific drive cycle before running Quick Test. This is necessary to detect certain faults not tested during KOEO or KOER Self-Tests. Malfunction Indicator Lamp (MIL) DTCs activate the "Check Engine" light in the instrument panel and are only generated for faults concerning the emission controls. Generally, non-MIL DTCs are for controls other than the emission system on the vehicle (i.e.; ACCS or TR faults).

Any scan tool that meets OBD II requirements can access Continuous Memory to retrieve MIL DTCs. However, when performing KOEO or KOER Self-Test or retrieving all Continuous DTCs, (MIL and non-MIL) with a generic scan tool, it will take additional manually entered commands.

During most diagnostic procedures, it is required that all DTCs be retrieved. It is necessary to use the enhanced diagnostic mode in the generic scan tool. Refer to Expanded Diagnostic Protocol. Expanded Diagnostic Protocol