Usage:
System Operation
The 3408 & 3412 Industrial Engines are equipped with an Electronic Control Module (ECM) to control fuel rate instead of using flyweights and linkages in the governor. The electronics also replace the mechanical fuel ratio control (FRC), torque control group and various adjustment screws.
The ECM uses several sensor input signals to control the rack movement. The ECM decides where to position the rack and then varies the voltage to the Brushless Torque Motor (BTM) to move the rack to the desired position. The rack position sensor is used so the ECM can sense the actual rack position for determining desired rack position.
Electronic Controls
The electronic control system consists of two main components, the Electronic Control Module (ECM) and the Personality Module. The ECM is the computer hardware which controls the engine. The Personality Module is the software which controls how the computer behaves.
Rack Controls
The rack mechanism on the engine is moved by a servo-valve which receives oil pressure from the fuel injection pump. However, the servo-spool is moved by a solenoid (BTM) rather than by a linkage, governor flyweights and springs.
The ECM determines a desired engine rpm based on the throttle position and customer specified parameters. The ECM maintains the desired engine rpm by sensing actual engine rpm using the primary engine speed (rpm) sensor or the secondary (backup) speed (rpm) sensor, then controlling the rack to achieve the desired engine rpm.
The ECM adjusts the voltage to the rack solenoid (BTM) to increase or decrease rack movement. (More voltage results in more rack movement.) The ECM senses how far the rack moved from the rack position sensor signal. The ECM increases or decreases the voltage to the rack solenoid until the rack is at the desired position.
The ECM sets certain limits on rack motion. FRC Rack (Fuel Ratio Control Rack) is a rack limit used to reduce the amount of acceleration smoke.
It operates similar to a mechanical engine FARC (Fuel Air Ratio Control). When the ECM senses a higher inlet manifold (boost) pressure (more air into cylinders), the FRC Rack limit is increased, which allows more fuel into the cylinders. Rated Rack is a rack limit based on rated power of the engine. It is similar to the rack stops and torque springs on a mechanical engine. It provides a power output limit and torque curves for a specific engine family and rating. All of these limits are programmed by the factory into the Personality Module.
Programmable Parameters
Certain parameters that affect the engine operation may be changed with an Electronic Service Tool (ECAP). These parameters are stored in the ECM.
These parameters are either System Configuration Parameters or Customer Parameters. System Configuration Parameters are those that affect power ratings or emissions. Customer Parameters are those that affect the Low Idle and High Idle Engine RPM Setting.
Passwords
System Configuration Parameters are protected by Factory Passwords. Customer Parameters are protected by Customer Passwords. The customer passwords are programmed by the customer.
Self-Diagnostics
The ECM has a limited ability to diagnose itself. When a problem is detected, a diagnostic code is generated and the diagnostic lamp flashes the diagnostic code. In most cases, the diagnostic code is also stored in the ECM permanent memory.
Diagnostic codes that represent current diagnostic codes are called ACTIVE. They indicate that a problem of some kind currently exists. They should always be serviced first.
Diagnostic codes stored in memory are called LOGGED. Since the problem may have been temporary, or may have been repaired since the time it was logged, logged diagnostic codes do not necessarily mean something needs to be repaired. Instead they are meant to be an indicator of probable causes for intermittent problems.
In addition, some logged diagnostic codes record events, rather than failures. Diagnostic codes not requiring passwords to clear are automatically deleted after 100 ECM operating hours. Refer to the topic in Section 4: Troubleshooting With A Diagnostic Code for more details.
Engine Overspeed
If the engine rpm exceeds 2230 rpm, the electronic control system will:
1. Shut down the rack signal from the ECM.
2. Shut down the rack signal to the rack actuator.
3. Activate the engine emergency air shutoff system by de-energizing the air shutoff solenoid.
PTO Mode
Closing the PTO Enable Switch allows the engine rpm to be controlled through a separate PTO increase/decrease speed switch. Initially, when the PTO Enable Switch is closed, the PTO desired speed becomes the same as desired speed from the primary throttle input. Then, as the PTO increase/decrease speed switch is used the desired engine rpm becomes the higher of the two speed inputs.
System Alarm Outputs
The electronic control system provides five different lamps to warn the operator about engine conditions. These lamps can be used to obtain status of Engine Low Oil Pressure, High Coolant Temperature, Low Coolant Level, Atmospheric Derate and a Diagnostic Lamp. The diagnostic lamp uses flash diagnostic codes to display the different diagnostic conditions present in the system. Refer to P-505: Alarm Lamp Circuit Test for additional Information.
The electronic control system provides four sinking drivers and one sourcing driver to annunciate the various conditions. The four sinking drivers are capable of sinking 200 mAmp and the sourcing driver is capable of sourcing 200 mAmp. The wiring harness provides a diagnostic connector output to allow the customer use of a relay, audible alarm or lamp for diagnostics. The diagram is an example of how to utilize the system alarm outputs.
The electronic control system provides for five optional alarm lamps to warn the operator about engine conditions. These lamps can be used to obtain status of Low Oil Pressure, High Coolant Temperature, Atmospheric Pressure Derate, Low Coolant Level and a Diagnostic Lamp. The diagnostic lamp uses flash diagnostic codes to display the different diagnostic conditions present in the system.
There are four sinking drivers which are capable of sinking 200 milliAmp. There is one sourcing driver which is capable of sourcing 200 milliAmp. The wiring harness provides a customer connector output and the customer can use the connector outputs to drive a relay, audible alarm or lamp. The diagram above is an example of how to utilize the system alarm outputs.
Customer Responsibility
Wiring Schematic
System Component Diagram
Engine Sensor and Connector Locations
Engine Sensor and Connector Locations
Connector Function and Pin Description
Electrical Connectors and Functions
Electronic Service Tools
The Caterpillar Electronic Service Tools for the electronic system are designed to help the service technician analyze and locate diagnostic codes or problems within the system.
The principle tool is the Electronic Control Analyzer Programmer (ECAP). It is able to communicate with the Electronic Control Module, to read diagnostic codes (CID-FMI), to read/monitor the various sensor output signals such as engine speed, rack position, or boost pressure, and to electronically calibrate the sensors such as boost pressure, throttle position and rack position.
The Electronic Service Tool is required to perform sensor calibrations, and to read or change engine/customer parameters. The basic tools have small plug-in modules, called Service Program Modules (SPM), to adapt the basic tools to the specific electronic engine application.
The ECAP (requires PWM adapter) can measure Pulse Width Modulated (PWM) signals, such as those produced by the Throttle Position Sensor.
There are several adapter cables, breakout T cables, probes, etc, that are used with the Electronic Service Tools in order to gain access for measurements of wires carrying voltages and signals. All multimeters listed in the following chart are suitable for making the necessary measurements. Other Special Tools include those needed to measure pressure or temperature.
Electronic Service Tools
