This system utilizes an engine mounted ECM with a replaceable PROM in the DDEC II ECM and an EEPROM in the DDEC II ECM. The ECM has isolator mounts for both vibration and electrical isolation. Depending upon application, some units have fuel cooling of the ECM. The engine mounted system simplifies vehicle wiring for greater reliability.
The DDEC II ECM is a microprocessor. It is the control center of the DDEC II system. See Figure 20002 .
Schematic Diagram of DDEC II
The DDEC II ECM is packaged in a die-cast aluminum housing with sealed connectors, see Figure 20002 . It is mounted on the left side of the engine block.
The DDEC II consists of the following:
The DDEC II ECM is a sealed, nonserviceable unit. Tag defective ECM for recore.
Before attempting any diagnosis of the system, read Section 2, "Basic Knowledge Required," and Section 3, "Testing the DDEC System," of the DDEC II Troubleshooting Guide, 6SE489. Basic mechanical checks should be made beforehand to verify that the problem is definitely related to the electrical portion of the system. If the basic mechanical checks fail to locate the problem, start the electrical diagnosis with the Troubleshooting Charts as described in the DDEC II Troubleshooting Guide, 6SE489, or DDEC III/IV Troubleshooting Guide, 6SE497.
DDEC II Diagnostic Data Reader
DDEC II Diagnostic Reader
Perform the following steps for ECM removal:
Perform the following steps for ECM installation:
Diesel engine exhaust and some of its constituents are known to the State of California to cause cancer, birth defects, and other reproductive harm.
If the diagnostic reader is not available, the following procedure can be used to read the fault codes using the "Check Engine" light on the dashboard of the vehicle. See Figure 20399 .
Dashboard Warning Lights
If the vehicle is equipped with an OEM supplied diagnostic switch, hold the switch in the "ON" position. This should be done with the ignition on and the engine not running.
If there is no diagnostic switch, locate the 12-pin Diagnostic Data Link (DDL) connector (DDEC II applications only) under the dash of the vehicle. See Figure 20400 .
Examples of Diagnostic Data Link (DDL) Connector
If the vehicle is equipped with an OEM supplied diagnostic switch, the switch must NOT be switched on when operating the vehicle. If this is done, the diagnostic mode line will be grounded, and the throttle will be forced to the idle position, affecting vehicle operation. This condition will not occur when a diagnostic reader is used.
These methods will cause the "Check Engine" light to begin flashing a code when the ignition is turned to the "ON" position. Code 25, for example, would be two flashes followed by a pause, followed by five more flashes. This code would indicate no trouble codes logged since the last system check. This flashing code will be repeated until the diagnostic switch is turned "OFF" or the jumper wire is removed from pins A and M (on DDEC II engines only).
If a code other than 25 is read, refer to the correct chart as instructed by the DDEC II Troubleshooting Guide, 6SE498, or DDEC III/IV Single ECM Troubleshooting Guide, 6SE497 for repair instructions.
Fault codes can be cleared from the DDEC II and III systems only by using a diagnostic reader. Follow the instructions supplied with the reader to clear the fault codes.
Note: Before beginning any repair procedures, the ignition switch must be in the "OFF" position.
Following are basic replacement procedures for the DDEC components. Components should NOT be replaced unless a defective unit has been concluded by the DDEC II Troubleshooting Guide , 6SE489, or DDECIII/IV Single ECM Troubleshooting Guide, 6SE497.