0335685 JOHNSON RETAINER, Outlet nipple to brkt.

Electronic Controls
The Electronic Control Module (ECM) consists of two main components, the control computer (hardware) and the Personality Module (software). The control computer is the microprocessor and electronic circuitry. The Personality Module contains the software for the control computer which stores operating maps that define power and torque curves. The two work together to control engine operation.
Figure 1.1 - Personality ModuleThe ECM governs engine rpm (refer to Figure 1.2) by controlling the amount of fuel delivered by the injectors. Desired engine rpm is determined by the Throttle Position Sensor signal and certain sensor readings. Some diagnostic codes may cause a derate that affects engine rpm. Actual engine rpm is measured by the Speed/Timing Sensor. The ECM determines how much fuel to inject to maintain desired engine rpm by sensing the actual engine rpm.Fuel Injection
The ECM controls the timing, duration (amount) and pressure of the fuel injected by varying signals to the injectors and the Injection Actuation Pressure Control Valve (IAPCV). The injectors will inject fuel ONLY if the injector solenoid is energized by a 105 volt signal from the ECM. By controlling the timing and duration of the 105 volt signal, and the injection actuation pressure, the ECM can control injection timing and the amount of fuel injected based on engine rpm, load, and other operating conditions.The ECM limits engine power and modifies injection timing and pressure during Cold Mode operation to increase startability, reduce warm up time, and reduce white smoke. Cold Mode is active if the engine oil temperature falls below a predetermined value and other conditions are met. It remains active until the engine has warmed or a time limit is exceeded.The ECM has factory programmed limits on the amount of fuel that can be injected. FRC Fuel Pos is a fuel limit for exhaust smoke control purposes that is based on the maximum allowable fuel-to-air ratio. When the ECM senses a higher Turbocharger Compressor Outlet Pressure (more air available), the FRC Fuel Pos limit is increased to allow more fuel into the cylinder. Rated Fuel Pos is a limit based on the power rating of the engine. It is similar to the rack stops and the torque spring on a mechanically governed engine. The Rated Fuel Pos determines maximum power and torque values for a specific engine family and rating. Rated Fuel Pos is programmed by the factory into the Personality Module.Programmable Parameters
System Configuration Parameters are parameters stored in the ECM that affect engine operation. The parameters are set at the factory and may be changed with an Electronic Service Tool ( ET - Electronic Technician or, to a limited extent, ECAP - Electronic Control Analyzer Programmer). However, a factory password may be required to change certain parameters.Self-Diagnostics
The engine has the ability to detect problems with it's inputs and outputs. When a problem is detected, a diagnostic code is generated and an audible or visible alarm may be present at the electronic display module. The diagnostic code is also stored in the ECM's permanent memory and can be read with an Electronic Service Tool.Current diagnostic codes are referred to as ACTIVE. An Active code indicates a problem currently exists. They should always be serviced first. Refer to Section 4: Troubleshooting With A Diagnostic Code for more information.Diagnostic codes stored in memory are called LOGGED. The problem may have been temporary or may have been repaired since the time it was logged. It is important to remember that it is possible to log faults whenever a component is disconnected and the keyswitch is in the ON position. Therefore, logged diagnostic codes do not necessarily mean something needs to be repaired. Logged diagnostic codes may be helpful indicators to determine intermittent problems.In addition to diagnostic codes, the ECM also records EVENTS (such as high coolant temperature or low oil pressure) that have occurred, rather than diagnostics or electronic problems. Refer to Section 4: Troubleshooting With A Diagnostic Code for more information.Passwords
Several System Configuration Parameters and most Logged Events are protected by Factory Passwords. Factory passwords are available only to Caterpillar dealers. Refer to Section 2: Programming Parameters for details regarding when passwords are needed and how to obtain them.Electronic Governor Diagram
Figure 1.2 - Electronic GovernorFuel System Block Diagram
Figure 1.3 - HEUI Fuel System Block DiagramBasic Engine Block Diagram
Figure 1.4 - 631E/637E 3408E Engine Block DiagramApplication Block Diagram
Figure 1.5 - 631E/637E Application Block DiagramEngine Component Diagrams And Model Views
Figure 1.7 - Engine View - Sensor LocationsElectrical Connectors And Functions 631E/637E Application Electronic Service Tools
The Caterpillar Electronic Service Tools are designed to help the service technician obtain and analyze data, and diagnose existing and potential problems within the electronic system. Their use is required to perform calibrations and to read or change programmable parameters.Two Caterpillar Electronic Service Tools can be used with the engine. The Electronic Technician (ET) or the Electronic Control Analyzer Programmer (ECAP). With either ET or ECAP, a Communication Adapter Tool is required to communicate with the Electronic Control Module (ECM). ET is the preferred Electronic Service Tool due to its increased functionality, however, the ECAP may be used to perform basic troubleshooting procedures.The digital multimeter is suitable for making the necessary voltage and resistance measurements. There are also several adapter cables, probes, etc, used with the Electronic Service Tools that allow the service technician to perform the required measurements needed for diagnosis. These tools are listed in the following tables and diagrams, along with their associated part numbers. Optional Service Tools
Two short jumper wires will be needed to check continuity of some wiring harness circuits. The jumper wires are used to short (connect) two adjacent pins or sockets together in a connector. Refer to the Service Tools Diagram for details on how to fabricate jumper wires.A long extension wire may be needed to check continuity of some wiring harness circuits. Refer to the Service Tools Diagram for details on how to fabricate an extension wire.The following list contains service tools that are not required, but may be helpful, to