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DDEC III/IV provides an indication of engine and vehicle malfunctions. The ECM continually monitors the DDEC III/IV system. See Figure 20003 and see Figure 38352 . ‪

DDEC III/IV System Series 60 Diesel Engine

DDEC III/IV System Series 60 Natural Gas Engine

Any faults that occur are stored as codes in the ECM's memory. These codes can be accessed in any of three ways: ‪

  1. A DDR can be used to read the codes. See Figure 21424 .
  2. A personal computer (PC) connected to the ECM through a translator device which converts J1708 to RS232 protocol can be used.
  3. The Check Engine Light (CEL) or the Stop Engine Light (SEL) is illuminated.
    • The CEL (panel mounted yellow indicator light) illuminated diagnose condition as soon as convenient.
    • The SEL (panel mounted red indicator light) and CEL illuminated, a major fault occurred and immediate attention required to avoid engine damage.
    • Automatic engine shutdown or rampdown is available as an option. A shutdown override switch is required to allow the vehicle to be moved to a safe location during automatic shutdown or rampdown.

DDEC III/IV features programmable with a Diagnostic Data Reader (DDR) are: ‪

  • Password
  • Droop
  • Active hp braking
  • Cruise control
  • Engine brake
  • Vehicle speed limiting
  • Vehicle speed sensor
  • Variable Speed Governor cruise switch
  • Idle timer shutdown
  • Idle timer between air temperatures
  • Vehicle ID number (VIN)
  • Idle adjustment
  • Progressive shifting
  • Engine protection

The hand-held DDR is used on engines equipped with DDEC III/IV 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-D , includes a reader, cable, carrying case, DDEC cartridge, manual, and a six-pin adaptor. See Figure 21424 . ‪

The DDR and Printer

The SAE Standard Communications of the DDEC III/IV system are listed in Table . The fan control inputs and outputs for DDEC III/IV are listed in Table . The engine brake control features of DDEC III/IV are listed in Table . DDEC III/IV 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/IV engine hardware is listed in Table . A comparison of DDEC II and DDEC III/IV standard sensors is listed in Table and a comparison of optional sensors is listed in Table . ‪

SAE Standard Communication

SAE J1587 protocol on J1708 hardware ‪

Diagnostics ‪

Electronic dashes ‪

Data Hub ‪

SAE J1922 protocol on J1708 hardware ‪

Traction control systems ‪

Transmission controls ‪

SAE J1939 high speed data link ‪

Vehicle controls ‪

SAE Standard Communications for DDEC III/IV



Coolant temperature ‪

Single on/off fan clutch ‪

Oil temperature ‪

Dual on/off fan clutch ‪

Air temperatures ‪

Two-speed single fan ‪

Air conditioning ‪

Modulated fan clutch ‪

Fan Controls for DDEC III/IV

Engine Brake Control

Eliminates OEM engine brake module ‪

Compatible with cruise control ‪

Engine brake will go on and off without disabling cruise control ‪

Engine fan braking ‪

Requires fan and engine brake control ‪

Fan turns 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 Brake Control with DDEC III/IV

Engine Hardware



Electronic Foot Pedal Assembly ‪

Three Wires ‪

Three or five wires ‪

Coolant Level Sensor ‪

Coolant Probe/Module ‪

Coolant Probe Only ‪

Diagnostic Request Stop Engine Override ‪

Two Separate Switches ‪

One Combined Switch ‪

Communications ‪

Vehicle Interface Harness SAE J1587/J1922 ‪

Vehicle Interface Harness SAE J1587 Communications Harness SAE J1922, SAE J1939 ‪

Power Harness ‪

6-Pin Connector ‪

5-Pin Square Connector ‪

Wiring ‪

16 gauge wire, 4 Power, 2 Ground ‪

12 gauge wire (Eliminates Splicing), 2 Power, 2 Ground ‪




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 ‪

Standard Sensors



Fuel Pressure ‪

Fuel Pressure ‪

Pressure Governor (Firetruck) ‪

Pressure Governor (Firetruck) ‪

Optional Sensors

Repair or Replacement of the DDEC III/IV Electronic Control Module

The DDEC III/IV ECM is a sealed, nonserviceable unit. Tag defective ECM for recore. ‪

Removal of the DDEC III/IV Electronic Control Module

Perform the following steps for ECM removal: ‪

  1. Carefully disengage the lock tab on the power harness and injector harness connectors when removing.
  2. Remove the two (2) wire and three (3) wire harness connections at the ECM.
  3. Remove the two 30-pin connectors.
  4. Remove the through-bolts holding the ECM to the engine.
  5. Remove the ECM and cold plate from the engine, if so equipped.
  6. Remove the screws securing the cold plate to the ECM. Remove the cold plate from the ECM, if so equipped.

Installation of the DDEC III/IV Electronic Control Module

Perform the following steps for ECM installation: ‪

  1. Install the cold plate on the ECM, if so equipped. Tighten the screws securing the cold plate to the ECM. Use Loctite 262, or equivalent, on the cold plate-to-ECM screws. Torque to 9.5-12 Nm (84-106 lbin.).
  2. Inspect the ECM isolators for damage and replace if required.
  3. Mount the ECM and cold plate to the engine.
  4. Secure the ECM to the engine with through-bolts. Torque the ECM-to-engine bolts to 23-27 Nm (17-20 lbft).
  5. Install the connectors in the ECM and torque the jack screws to 2.493.16 Nm (2228 lbin).
  6. Engage the lock tab on the power harness and injector harness connectors.
  7. Turn the ignition to the "ON" position. Observe the DDR for any diagnostic code(s). If any code(s) other than code 25 is logged, refer to the Detroit Diesel DDEC III/IV Single ECM Troubleshooting Manual (6SE497).


    Diesel engine exhaust and some of its constituents are known to the State of California to cause cancer, birth defects, and other reproductive harm.

    • Always start and operate an engine in a well ventilated area.
    • If operating an engine in an enclosed area, vent the exhaust to the outside.
    • Do not modify or tamper with the exhaust system or emission control system.
  8. Start the engine, and check for leaks.