Continuous Memory DTC Access: Overview

PURPOSE
The purpose of this mode is to enable the scan tool to obtain stored Diagnostic Trouble Codes (DTCs). All scan tools 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 03 request. Specific menu access to emission related DTCs (MIL only) is determined by the scan tool manufacturer. Most vehicles also support OBD II Mode 07 request for pending MIL DTCs. The purpose of this mode is to assist in repair verification, by reporting a pending DTC after one drive cycle. The pending DTC does not necessarily indicate a damaged component or system. If the test indicates a failure after additional driving, then the MIL will be illuminated and a DTC will be set and reported with OBD II Mode 03, Emission Related Continuous Memory DTCs access.

DESCRIPTION
Continuous Memory DTC access is also a self-test of the powertrain control system. Unlike the KOEO and KOER self-tests, which can only be activated on demand, the Continuous Self-Test is always active. The test consists of all the OBD II monitors, and the Comprehensive Component Monitor, and is designed to detect failures contributing to driveablity 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 dealing with 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.

It is also possible to access MIL DTCs that are pending and have not actually turned on the MIL when using a generic scan tool. This applies to all vehicles except Continental, Ranger and 3.0L Windstar. A pending DTC applies to a fault set during the first drive after a PCM reset that has not turned on the Malfunction Indicator Lamp. Pending DTC retrieval is useful for a repair verification without the need to drive the vehicle through more than one drive cycle. Previously, a MIL DTC was not accessible by a generic scan tool until after the MIL was on.

During most diagnostic procedures in this manual, it is required that all DTCs be retrieved. It is necessary to use either the NGS Diagnostic Data Link Menu or the Expanded Diagnostic Protocol (EDP) mode in the generic scan tool.