Introduction

994D Wheel Loader

The 994D Wheel Loader is equipped with the latest state-of-the-art electronic machine control and monitoring technology. This guide provides a general overview of each electronic system along with a troubleshooting guide which explains how to use the various troubleshooting tools, techniques and component locations.

Features

Power Train Electronic Control System

Power Train Electronic Control System Block Diagram

The Power Train Electronic Control System performs the shifting of the transmission. The electronic control module (ECM) responds to the shifting requests of the operator by activating the appropriate clutch solenoid valves which then allow oil to flow to the corresponding transmission clutches. In addition to the shifting function, the ECM also controls the neutral start function and the backup alarm function.

* STIC Controller - The direction, upshift and downshift switches, located in the STIC controller, tell the ECM the requests of the operator; forward, reverse, neutral, upshift or downshift. The ECM acts upon the shift requests by activating the appropriate transmission clutch solenoid valves. Except for certain conditions, the ECM shifts the transmission as requested by these switches.

* Transmission Clutch Solenoid Valves - These clutch solenoid valves, located on the transmission, direct pilot oil to the ends of the control spool. The control spool will shift allowing pressure oil to the corresponding clutches. The ECM decides which clutch solenoid valves to activate, based on the input from the direction, upshift and downshift switches (STIC controller). Clutch solenoid valves 1 and 2 are for direction. Clutch solenoid valves 3, 4, and 5 are for speed. For movement of the machine two clutch solenoid valves are activated; one for direction and one for speed. When in neutral, only clutch solenoid valve 3 is activated.

Also featured is a electronic torque converter. The ECM controls the impeller clutch and lockup clutch functions of the torque converter. These machines also have an additional feature called Reduced Rimpull. This allows the operator to select a preset amount of rimpull reduction desired.

The power train ECM communicates with other electronic controls on the machine using the CAT data link. This data link allows the power train ECM to send and receive information throughout the machine between the various control modules. The CAT data link is not a visible component.

Calibration and service code information can also be shown on the service tools, Caterpillar Electronic Technician and VIMS-PC.

For detailed information on operation and troubleshooting of the power train system, refer to RENR2522, Power Train Electronic Control System.

Vital Information Management System (VIMS)

Vital Information Management System (VIMS) Block Diagram

VIMS Message Center Module
(1) Alert indicator. (2) Data logging indicator. (3) Message area. (4) Universal gauge. (5) Gauge warning area.

Keypad
(6) Backward arrow key. (7) Forward arrow key. (8) Gauge key. (9) Key pressed indicator.

The Vital Information Management System (VIMS) are electronic monitoring systems that continuously monitor machine systems. The main VIMS module makes decisions based upon input from the VIMS interface module(s), VIMS keypad, other electronic control modules on the machine and internal calculations. The main module sends information to the VIMS interface module(s) and other electronic control modules on the machine. The input and output of this information takes place over the CAT Data Link. VIMS is the standard equipment on the 994D. VIMS consists of two interface modules, a main module, a keypad, display components and various switches, sensors, solenoids, lamps and alarms. VIMS has the additional capability of providing historical machine and operator data which can be used to analyze and forecast machine problems.

VIMS alerts the operator of abnormal machine conditions that exist. All abnormal machine conditions are called machine events. VIMS also alerts the operator of system faults of other electronic modules on the machine and of VIMS itself. These system faults are called system events. VIMS stores information about each event (machine and system) to assist service personnel in machine maintenance and troubleshooting.

MACHINE events are those that relate to a machine system. An example of a machine event is: engine coolant temperature high. In most every case, the operator needs to respond to the event. When an event is present, pressing the "F1" key will show more information to the operator on the second line of the message center area. During temperature warnings, the F1 key will cause the display to show the actual temperature of the machine system.

SYSTEM events are those relating to an electrical system problem where a service technician needs to make a repair. An example of a system event is: signal voltage of coolant temperature sensor is above normal. When such an event is present, pressing the "F1" key will display the service codes Module Identifier (MID), Component Identifier (CID), and Failure Mode Identifier (FMI).

NOTE: When VIMS is receiving a machine event and a system event regarding the same machine condition (such as coolant temperature), VIMS can determine if the sensor is actually faulty or if the coolant temperature is too high.

For detailed information on the Vital Information Management System, refer to SENR6059, Service Manual, Vital Information Management System (VIMS).

Payload Control System

VIMS Payload Control System Block Diagram

The Payload Control System on the 994D is an option which is included in and controlled by the VIMS. The VIMS Payload Control System is an advanced electronic system designed to provide accurate material weighing. The VIMS Payload Control System can not only calculate bucket and truck load weights, but can also display and store this information for later retrieval. The VIMS message center and keypad are the primary interface to the operator. The main module receives lift cylinder pressure and position from the interface module via the Cat data link. Additional hardware requirements are a "Payload Store" button and an optional printer in the cab.

The standard VIMS RS-232 interface to off-board systems is the method used to upload the desired VIMS configuration from the service tool. It is also used to download machine productivity information to the laptop for later analysis.

NOTE: The printer and broadcast interfaces are shown as two lines coming from the VIMS main module, but they are actually the same line. This one line will have both a printer and broadcast port, but the operator must choose between one or the other since both cannot be supported simultaneously.

For detailed information on the operation of the VIMS Payload Control System, refer to SEBU7145, Operation And Maintenance Manual, 994D Wheel Loader. For Service information, refer to SENR6059, Service Manual, Vital Information Management System (VIMS).

Engine Control

The 3516B Engine in the 994D Wheel Loaders is designed for electronic control of most engine functions. The engine electronic system consists of an Electronic Control Module (ECM), Hydraulic Electronic Unit Injectors, Injection Actuation Pressure Control Valve (APCV), wire harness, switches, solenoids, and sensors. All of these components work together to monitor and control the engine operation.

The 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 is the software for the control computer which stores the operating maps that define power and torque curves. The two work together to control engine operation.

The ECM governs engine rpm by controlling the amount of fuel delivered by the injectors. Desired engine operation is determined by the throttle position sensor signal and certain sensor readings. Some diagnostic codes may cause a derate that effects desired engine rpm. Actual engine rpm is measured by the Speed/Timing Sensor.

For service information refer to SENR1123, Systems Operation, Testing & Adjusting, 994D Wheel Loader Engine.