DDEC III provides an indication of engine and vehicle malfunctions. The ECM continually monitors the DDEC III system. See Figure 20003 and see Figure 38352 .
DDEC III System Series 50 Diesel
DDEC III System Series 50 Natural Gas
Any faults that occur are stored as codes in the ECM's memory. These codes can be accessed in any of three ways:
DDEC III features programmable with a Diagnostic Data Reader (DDR) are:
The hand-held DDR is used on engines equipped with DDEC III to display engine description, diagnostic data, fault codes, and to program the ECM calibration. A printout of the information displayed on the DDR, can be obtained by attaching a printer. The diagnostic data reader kit, J 38500-1DD , includes a reader, cable, carrying case, DDEC cartridge, manual, and a 6-pin adaptor. See Figure 21424 .
Note: S50G GFI controlled fuel systems that have been converted to DDEC III controlled close loop fuel system will not have an oil temperature sensor.
The DDR and Printer
The SAE Standard Communications of the DDEC III system are listed in Table . The fan control inputs and outputs for DDEC III are listed in Table . The engine brake control features of DDEC III are listed in Table . DDEC III can identify faulty components and other engine-related problems by providing the technician with a diagnostic code. A comparison of DDEC II and DDEC III engine hardware is listed in Table . A comparison of DDEC II and DDEC III standard sensors is listed in Table and a comparison of optional sensors is listed in Table . Standard sensors for the S50G are listed in Table .
DDEC III and DDEC II Electronic Control Module (ECM)
SAE Standard Communication |
SAE J 1587 protocol on J 1708 hardware |
Diagnostics |
Electronic dashes |
Data Hub |
SAE J 1922 protocol on J 1708 hardware |
Traction control systems |
Transmission controls |
SAE J 1939 high speed data link |
Vehicle controls |
Inputs |
Outputs |
Coolant temperature |
Single on/off fan clutch |
Oil temperature |
Dual on/off fan clutch |
Air temperature |
2-speed single fan |
Air conditioning |
Modulated fan clutch |
Engine Brake Control |
Eliminates OEM engine brake module |
Compatible with cruise control |
Engine brake will go and off without disabling cruise control |
Engine fan braking |
Requires fan and engine brake control |
Fan turn on when engine brake is on high |
In cruise control, engine brake operates electronically |
MPH activating speeds are set with DDR |
Cruise control, engine brake operates manually |
Engine Hardware |
DDEC II |
DDEC III |
Electronic Foot Pedal Assembly |
3 Wires |
3/4 Wires |
Coolant Level Sensor |
Coolant Probe/Module |
Coolant Probe Only |
Diagnostic Request Stop Engine Override |
2 Separate Switches |
1 Combined Switch |
Communications |
Vehicle Interface Harness SAE J 1587/J 1922 |
Vehicle Interface Harness SAE J 1587 Communications Harness SAE J 1922, SAE J 1939 |
Power Harness |
6 Pin Connector |
5 Pin Square Connector |
Wiring |
16 gage wire, 4 Power, 2 Ground |
12 gage wire (Eliminates Splicing), 2 Power, 2 Ground |
DDEC II |
DDEC III |
Oil Temperature (Truck) |
Oil Temperature |
Oil Pressure |
Oil Pressure |
Coolant Level |
Coolant Level |
Turbo Boost |
Turbo Boost |
Throttle Position (OEM Supplied) |
Throttle Position |
Timing Reference |
Timing Reference |
Synchronous Reference |
Synchronous Reference |
Fuel Temperature |
Fuel Temperature, Air Temperature |
DDEC II |
DDEC III |
Fuel Pressure |
Fuel Pressure |
Pressure Governor (Firetruck) |
Pressure Governor (Firetruck) |
Low Pressure Fuel System |
High Pressure Fuel System |
Oil Temperature |
Exhaust Temperature |
Oil Pressure |
Oil Pressure |
Coolant Temperature |
Coolant Temperature |
Coolant Level |
Coolant Level |
Turbo Boost (Inlet Manifold Pressure) |
Turbo Boost (Inlet Manifold Pressure) |
Timing Reference |
Timing Reference |
Synchronous Reference |
Synchronous Reference |
Fuel Temperature |
Fuel Temperature |
Air Inlet Temperature |
Air Inlet Temperature |
Throttle Position |
Throttle Position |
Knock |
Knock |
|
Exhaust Gas Oxygen |
|
Barometric Pressure |
|
Fuel Pressure |
The DDEC III ECM is a sealed, nonserviceable unit. Tag defective ECM for recore.
Perform the following steps for ECM removal:
Perform the following steps for ECM installation:
![]() PERSONAL INJURY |
Diesel engine exhaust and some of its constituents are known to the State of California to cause cancer, birth defects, and other reproductive harm.
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A water shield may be installed on the vertically mounted ECM of DDEC III on-highway or coach engines. The water shield prevents the intrusion of high pressure water into the 30-pin and power plug connections of the ECM, which may cause corrosion of the terminals. Perform the following steps for removal of the ECM water shield:
![]() EYE INJURY |
To avoid injury from flying debris when using compressed air, wear adequate eye protection (face shield or safety goggles) and do not exceed 40 psi (276 kPa) air pressure. |
1. Bolts (2)
4. Cylinder Block
2. Water Shield
5. Electronic Control Module
3. Cold Plate
6. Engine Wiring Harness
Electronic Control Module Related Parts with Cold Plate
Inspect the water shield for cracks or other damage which could allow water to enter the ECM connections, resulting in possible corrosion of the terminals. Replace the water shield if cracked or damaged.
Install the ECM water shield as follows:
![]() EYE INJURY |
To avoid injury from flying debris when using compressed air, wear adequate eye protection (face shield or safety goggles) and do not exceed 40 psi (276 kPa) air pressure. |
1. Electronic Control Module
2. Mounting Boss
Electronic Control Module 30-Pin Location
1. Bolts (2)
4. Cylinder Block
2. Water Shield
5. Electronic Control Module
3. Cold Plate
6. Engine Wiring Harness
Electronic Control Module Water Shield with Cold Plate
1. Bolts (2)
4. Electronic Control Module
2. Water Shield
5. Engine Wiring Harness
3. Cylinder Block
Electronic Control Module Related Parts without Cold Plate
![]() PERSONAL INJURY |
Diesel engine exhaust and some of its constituents are known to the State of California to cause cancer, birth defects, and other reproductive harm.
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