PREVOST H3-41 Manual page 60

DETROIT DIESEL ELECTRONIC
CONTROL (DDEC) SYSTEM
DDEC is an advanced-technology electronic fuel
injection and control system for Detroit Diesel
engines. As an integral part of the engine, the
DDEC system provides a number of performance
features and driver benefits; including, improved
fuel economy and performance, reduced cold
smoke, and reduced maintenance and repair cost.
These advantages are obtained by optimizing
control of the critical engine functions which affect
fuel economy, engine
performance of the injectors.
Its major components include an Electronic
Control Module (ECM), Electronic Unit Injectors
(EUI), electronic throttle pedal and sensors. The
ECM, which provides central processing and
control of the DDEC system, contains the
following:
- A microprocessor that continuously monitors
and analyzes the engine's performance using
sensors during engine operations.
- Flash Random Access Memory (FRAM) that
stores ECM runtime software, which contains
engine control instructions.
- Electrically Erasable, Programmable, Read-
Only Memory (EEPROM) that provides
instructions for basic engine control functions
such as rated speed and power, engine
governing, cold start logic and diagnostics,
and an engine protection system.
OTHER FEATURES
reliability and the
The Electronic Unit Injectors (EUI) operate on a
principle similar to the mechanical unit injector
system. However, a solenoid-operated control
valve performs the injection timing and metering
functions which make injector timing much
simpler and more precise.
DDEC provides
diagnosing system malfunctions with a self-
diagnostic system.
monitors all engine sensors and electronic
components and recognizes system faults and
other engine-related problems by providing the
technician with a diagnostic code.
system will illuminate the dashboard CHECK
ENGINE and STOP ENGINE indicators which are
integral parts of the electronic diagnostic system.
These lights are designed to indicate a problem
and transmit a coded signal to the technician to
locate the defective component.
troubleshooting and obtain pertinent data logged
in the ECM (Electronic Control Module) memory,
a Diagnostic Data Reader (DDR) can be used (not
supplied by manufacturer). Plug the DDR into the
receptacle on the bottom of the side panel of the
L.H. control panel.
depress the stop engine OVERRIDE switch on the
L.H. lower control panel (refer to the "Controls &
Instruments" section). Active and inactive codes
will flash respectively the STOP ENGINE and the
CHECK ENGINE indicators. Refer to "Technical
Information" section under "DDEC III Diagnostic
Codes".
4-1
H3-41 & 45
the capability of quickly
The self-diagnostic system
The DDEC
To facilitate
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