Diagnostic System Operation

The ECM of the DEC system is equipped with a self-diagnostic system which detects system failures or abnormalities. However, the system does not store trouble codes or provide a visual display of malfunctions. To determine the cause of driveability problems, a Diesel Diagnostic Check (DDC) tester (J 34750 or equivalent) must be connected to the system. See Fig 1 .

Fig 1: Diesel Diagnostic Check Tester. This tester must be used to determine system failures.

The DDC tester must be used to accurately diagnosis the cause of any problems which may be related to the DEC system. This is the only special tool required to service the DEC system.

An Assembly Line Data Link (ALDL) connector located under left side of instrument panel (under driver's seat on van models) is used by factory technicians to check the system prior to shipment. This ALDL connector is also used to make specific checks on the system by service personnel. See Fig 2 .

Fig 2: ALDL Connector Identification. Located under left side of dash on pickup models and under driver's seat on van models.