ELECTRONIC TROUBLESHOOTING 3176 DIESEL TRUCK ENGINE Caterpillar

Glossary Of Terms

Usage:

Aftermarket device: A device or accessory installed by the customer after the vehicle is delivered.
Air-To-Air Aftercooler (ATAAC): A means of cooling intake air after the turbocharger, using ambient air for cooling. The intake air is passed through an aftercooler (heat exchanger) mounted in front of the radiator before going to the intake manifold.
Alternating Current (AC): The type of current where the direction of current flow changes (alternates) regularly and constantly.
American Wire Gauge (AWG): A measure of the diameter (and therefore the current carrying ability) of electrical wire. The smaller the AWG number, the larger the wire.
Before Top Dead Center (BTDC) or Before Top Center (BTC): The 180° of crankshaft rotation before the piston reaches Top Dead Center (normal direction of rotation).
Boost Pressure Sensor: This sensor measures inlet manifold air pressure and sends a signal to the ECM.
Bypass Circuit: A circuit, usually temporary, to substitute for an existing circuit, typically for test purposes.
Calibration: As used here, is an electronic adjustment of a sensor signal.
Cruise Control Range: The range that the cruise control can operate within. Usually limited to the speed range anticipated on the open road.
Code: See Diagnostic Code.
Customer Specified Parameter: A Parameter that can be changed and whose value is set by the customer. Protected by Customer Passwords.
Data Link: An electrical connection for communication with other microprocessor based devices that are compatible with the American Trucking Association and SAE Standard such as, trip recorders, electronic dashboards, and maintenance systems. The Data Link is also the communication medium used for programming and troubleshooting with Caterpillar service tools.
Desired RPM: An input to the electronic governor within the ECM. The electronic governor uses inputs from the Throttle Position Sensor, Engine Speed Sensor, Cruise Control, and Customer Parameters to determine "Desired RPM".
Desired Timing Advance ("Des Timing Adv" on ECAP): The injection timing advance calculated by the ECM as required to meet emission and performance specifications.
Diagnostic Code: Sometimes referred to as a "fault code", it is an indication of a problem or event in the 3176 System.
Diagnostic Lamp: Sometimes referred to as the "check engine light", it is used to warn the operator of the presence of an active diagnostic code.
Digital Diagnostic Tool (DDT): A Caterpillar Electronic Service Tool used for programming and diagnosing of the 3176 System.
Direct Current: The type of current where the direction of current flow is consistently in one direction only.
Duty Cycle: See Pulse Width Modulation.
Electronic Control Analyzer and Programmer (ECAP): A Caterpillar Electronic Service Tool used for programming and diagnosing a variety of electronic controls. An ECAP is needed for advanced diagnostic and programming functions not possible with a DDT.
Electronic Control Module (ECM): The engine control computer that provides power to the 3176 electronics, monitors 3176 inputs and acts as a governor to control engine rpm.
Electronic Engine Control (3176): The complete electronic system that monitors and controls engine operation under all conditions.
Electronically Controlled Unit Injector: The injection pump which is a mechanically actuated, electronically controlled unit injector combining the pumping, electronic fuel metering and injecting elements in a single unit.
Engine Speed/Timing Sensor: Provides a Pulse Width Modulated Signal to the ECM, which the ECM interprets as crankshaft position and engine speed.
Estimated Dynamic Timing: The ECM's estimate of actual injection timing.
Fuel Ratio Control (FRC): FRC Fuel Pos. - is a limit based on control of the fuel-air ratio and is used for emissions control purposes. When the ECM senses a higher boost pressure (more air into cylinder), it increases the "FRC Fuel Pos" limit (allows more fuel into cylinder).
Fuel Position: An internal signal within the ECM, from the Electronic Governor to Fuel Injection Control. It is based on desired rpm, FRC Fuel Position, rated fuel position and engine rpm. Reference "3176 System Overview" in Section 1 of this manual.
Fuel Pressure Sensor: This sensor measures engine fuel pressure and sends a signal to the ECM.
Harness: The wiring bundle connecting all components of the 3176 System.
Hertz (Hz): Measure of frequency in cycles per second.
Open Circuit: Condition where an electrical wire or connection is broken, so that the signal or the supply voltage can no longer reach its intended destination.
Original Equipment Manufacturer (OEM): As used here, the manufacturer of a vehicle in which a Caterpillar engine is installed.
Parameter: A programmable value which affects the characteristics or behavior of the engine and/or vehicle.
Password: A group of numeric or alpha-numeric characters, designed to restrict access to parameters. The 3176 System requires correct passwords in order to change Customer Specified Parameters (Customer Passwords) or certain engine specifications (Factory Passwords). Passwords are also required to clear certain diagnostic codes.
Personality Module or Ratings Personality Module: The module connected to the ECM which contains all the instructions (software) for the ECM and performance maps for a specific horsepower family.
Progressive Shifting: Shifting up through the lower gears quickly by not winding up the engine in each gear. Shifts are made above peak torque but below rated rpm. Needlessly winding up the engine into the higher rpm ranges before shifting to the next gear wastes fuel and fails to take advantage of the torque rise of the engine. The two steps (LoGr1, LoGr2) approximate ideal progressive shifting. Low Gear #1 is typically set no lower than Peak Torque RPM + 200 RPM. Low Gear #2 is typically set midway between Low Gear #1 RPM limit and Top Engine Limit.
Power Take Off (PTO): Operated with the cruise control switches, this mode permits setting constant engine RPM when the vehicle is not moving (like a manual throttle control cable).
Pulse Width Modulation (PWM): A signal consisting of variable width pulses at fixed intervals, whose "TIME ON" versus "TIME OFF" can be varied (also referred to as "duty cycle").

Example of Pulse Width Modulation Signals
Rated Fuel Position: ("Rated Fuel Pos" on ECAP) - this indicates the maximum allowable fuel position (longest injection pulse). It will produce rated power for this engine configuration.
Reference Voltage: A regulated voltage supplied by the ECM to a sensor. The reference voltage is used by the sensor to generate a signal voltage.
Retarder Enable Signal: The retarder enable signal interfaces the ECM to the engine retarder. This will prohibit operation of the engine brake during undesirable engine operating conditions (such as while the engine is being fueled).
Sensor: A device used to detect and convert a change in pressure, temperature, or mechanical movement into an electric signal.
Service Program Module (SPM): A software program on a factory programmable computer chip, designed to adapt an ECAP or DDT to a specific application.
Short Circuit: A condition where an electrical circuit is unintentionally connected to an undesirable point. Example: a wire which rubs against a vehicle frame until it makes electrical contact.
Signal: A voltage or waveform used to transmit information, typically from a sensor to the ECM.
Speed "burp": A sudden brief change in engine speed.
Speed/Timing Sensor: Provides a PWM signal to the ECM, which the ECM interprets as engine speed and crankshaft position.
Subsystem: as used here, it is a part of the 3176 System that relates to a particular function, for instance: vehicle speed subsystem, etc.
Supply Voltage: A constant voltage supplied to a component to provide electrical power for its operation. It may be generated by the ECM, or it may be vehicle battery voltage supplied by the vehicle wiring.
'T' Harness: A test harness designed to permit normal circuit operation while measuring voltages, typically inserted between the two ends of a connector.
Throttle Position: The ECM's interpretation of the signal from the throttle position sensor.
Throttle Position Sensor: An electronic sensor which is connected to the accelerator pedal and sends a Pulse Width Modulated Signal to the ECM.
Total Tattletale: Total number of changes to all customer specified parameters.
Transducer: A device that converts a mechanical signal to an electrical signal.
Transducer Module: A sealed unit mounted on one end of the ECM, which contains the engine Boost Pressure Sensor.
Vehicle Speed Buffer: A device used to condition and amplify the output of the Vehicle Speed Sensor.
Vehicle Speed Sensor: An electro-magnetic pickup that measures vehicle speed from the rotation of gear teeth in the drive train of the vehicle.