This system utilizes an engine mounted EDU and a cab mounted ECM, which has a replaceable Programmable Read-Only Memory (PROM). The EDU functions as the high current switching unit for the actuation of the injector solenoids and is fuel-cooled.
The DDEC I ECM is a microprocessor. It is the control center of the DDEC I system. See Figure 20001 .
Schematic Diagram of DDEC I
The DDEC I ECM is packaged in a die-cast aluminum housing with sealed connectors. See Figure 20402 .
The DDEC I system consists of the following:
Electronic Control Module - DDEC I
It is usually mounted inside the passenger compartment of the vehicle.
DDEC I ECM is a sealed nonserviceable unit.
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, refer to the Detroit Diesel Single ECM Troubleshooting Manual (6SE497). Start by reading the "Basic Knowledge Required" section before attempting to diagnosis electrical faults.
The DDL Reader can only be used on DDEC I engines. See Figure 20396 .
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.
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. See Figure 20399 .
To avoid injury from electrical shock, follow OEM furnished operating instructions prior to usage.
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. The throttle will also go to idle if pins A and M in the DDL connector are jumpered together. 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.
If any code(s) other than code 25 is logged, refer to the Detroit Diesel Single ECM Troubleshooting Manual (6SE497).
Fault codes can be cleared from the DDEC I system by interrupting the power flow to the ECM. This can be accomplished by turning the ignition to the OFF position and removing the 5-amp ECM fuse for ten seconds or more. See Figure 20401 .
Typical Electronic Control Module Power Fuse Panel
Note: Some OEMs will use circuit breakers. Follow the OEM schematic. Some OEMs will use a different fuse plate configuration than the one shown. See Figure 20401 .
Note: Before beginning any repair procedures, the ignition switch must be in the OFF position.
The following section(s) are basic replacement procedures for the DDEC components. Components should NOT be replaced unless a defective unit has been concluded by the Detroit Diesel Single ECM Troubleshooting Manual (6SE497).
Perform the following steps for ECM removal:
Perform the following steps for ECM installation: