Note: The ECM is not serviceable. If the ECM is damaged, the ECM must be replaced. The ECM failure is unlikely. If the ECM failure is suspected, contact the Technical Communicator at a local dealership for possible consultation with Caterpillar before replacing the ECM. Replace the ECM only after all the other possible causes of a particular problem have been investigated.
Inorder toaid in diagnostics of certain types of electrical circuits that are controlled by the ECM, an internal "pull up voltage" is connected to ECM switch and sensor signal input contacts. An above normal voltage is internally connected to the ECM signal input circuit through a resistor.
During normal operation, the switch or sensor signal will hold the circuit low or at a certain signal amplitude, however, circuit conditions such as a loss of power to the component, a disconnection, or an open circuit will allow the circuit to be pulled high by the ECM pull-up voltage. The pull-up voltage will result in an above normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 03 (voltage above normal) diagnostic code for the affected circuit.
The types of ECM input circuits that have pull up voltage present are:
- Pulse Width Modulated (PWM) sensor input circuits
- Switch to ground switch input circuits
- Active analog (voltage) input signal circuits
- Passive analog (resistance) input signal circuits
Inorder to aid in diagnostics of electrical circuits that are controlled by the ECM, an internal "pull down voltage" is connected to ECM switch to battery type input circuits.
During normal operation, the switch contacts that are allowing the connection to a voltage source will hold the circuit high. When circuit conditions such as a loss of power to the switch supply voltage, a disconnection in the switch circuit or an open circuit will allow the circuit to be pulled low by the ECM pull-down voltage. The pull-down voltage will result in a below normal voltage condition at the ECM contact. As a result, the ECM will activate an FMI 04 (voltage below normal) diagnostic code for the affected circuit.
The machine has several different types of input devices. The ECM receives machine status information from the input devices and determines the correct output action that is needed in order to control machine operations based on memory and software parameters. The machine utilizes the following types of inputs: switch type and sensor type.
Switches provide signals to the switch inputs of the ECM. The possible outputs of a switch are listed: an open signal, a grounded signal and + battery signal.
Sensors provide an electrical signal to the ECM that constantly changes. The sensor input to the ECM can be one of several different types of electrical signals such as: pulse width modulated (PWM) signals, voltage signals, and frequency input signals. Refer to the correct pilot machine schematic to verify each input to the ECM.
The ECM sends electrical signals through the outputs. The outputs can create an action or the outputs can provide information to the ECM. The ECM can send output signals to the system components in one of several different electrical signal types such as: driver outputs, sinking driver outputs, sensor power supply outputs, and data link outputs. Refer to the correct pilot machine schematic to verify each output to the ECM.
Communication between the ECM and the other control modules on the machine is conducted over data link circuits. The data link circuits allow the sharing of information with other electronic control modules. The data link circuits are bidirectional. The data link circuit allows the ECM to send information and to receive information.
The ECM supports two types of data link systems.
- Cat® Data Link
- SAE J1939 Data Link
The two types of data links are the main structure for communication between all the control modules on the machine. More than one CAN data link system can be present on a machine. Dedicated CAN data link circuits can be used for communication between specific controls on the machine.
Communication between the ECM and the other control modules on the machine are conducted over the J1939 Data Link circuit that is connected to each control module. The ECMs use the Cat Data Link to send and receive information from the Cat® Electronic Technician (Cat ET) Service Tool.
A module identifier (MID) is assigned to each ECM on a machine. For example, the MID for the Machine ECM is 299.
| Contact Description for Connector J1 | ||
|---|---|---|
| No. | Function | Type |
| 1 | Hydraulic Lock Solenoid | Driver Low Side Return |
| 2 | Swing Solenoid Left | PWM Driver 1 |
| 4 | Swing Solenoid Right | PWM Driver 2 |
| 5 | Swing Brake Unlock | Sourcing Driver 1 |
| 6 | Hydraulic Lockout | Sourcing Driver 2 |
| 7 | Engine Start Relay | On/Off Sourcing Driver 1 |
| 8 | Travel Sped Shift | On/Off Sourcing Driver 2 |
| 9 | Quick Coupler Wedge | On/Off Sourcing Driver 3 |
| 10 | Boom Raise | PWM Driver 3 |
| 11 | Stick In | PWM Driver 14 |
| 12 | Stick Out | PWM Driver 13 |
| 13 | Bucket / Stick Return | PWM Return |
| 14 | Analog Sensor Return | Return |
| 15 | Return | Return |
| 16 | Governor | Sinking Driver 1 |
| 17 | Bucket Dump | PWM Driver 16 |
| 18 | Boom Low Leak Check | On/Off Sourcing Driver 5 |
| 19 | Hydraulic Lock Solenoid | On/Off Sourcing Driver 6 |
| 21 | Start Relay | Return |
| 22 | Blower Relay | Return |
| 23 | Travel Alarm Relay | Sinking Driver 3 |
| 24 | Washer Pump Relay | Sinking Driver 2 |
| 29 | Left Travel Pressure Switch | Switch to Ground |
| 29 | Quick Coupler Solenoid | Return |
| 30 | Hydraulic Lockout Switch | Return |
| 31 | A/C Compressor Relay | Sinking Driver 5 |
| 32 | Glow Plug Relay | Sinking Driver 4 |
| 33 | Fuel Level Sender | Passive Analog Input 1 |
| 34 | Hydraulic Oil Temperature Sensor | Passive Analog Input 2 |
| 35 | Left Joystick Left/Right Position Sensor | PWM / Frequency Input 1 |
| 36 | Boom / Swing Solenoid | Return |
| 37 | Left Joystick FWD/Reverse Position Sensor | PWM / Frequency Input 2 |
| 38 | Right Joystick Left/Right Position Sensor | PWM / Frequency Input 3 |
| 40 | Machine Lighting Relay | Sinking Driver 6 |
| 41 | Right Joystick FWD/Reverse Position Sensor | PWM / Frequency Input 4 |
| 42 | Left Joystick Thumbwheel | PWM / Frequency Input 5 |
| 43 | Engine Oil Pressure Switch | Switch to Ground Input 13 |
| 46 | Bucket Curl | PWM Driver 15 |
| 48 | Main Power Relay | Sinking Driver 8 |
| 49 | Wiper Relay | Return |
| 54 | Hydraulic Lock Out Switch | Switch to Ground Input 16 |
| 56 | 8V Power Supply | 8V Supply |
| 57 | Boom Lower | PWM Driver 4 |
| 62 | Hydraulic Lockout Switch | Switch to Ground Input 15 |
| 63 | Right Joystick Thumbwheel | PWM / Frequency Input 6 |
| 64 | 5V Supply 1 | 5V Supply 1 |
| 65 | Electronic Pump Solenoid | PWM Driver 5 |
| 69 | Key Switch Run | Key Switch Input |
| 70 | Blade Lever for Blade Lift Control | PWM / Frequency Input 7 |
| 71 | VAB/AUX/POB Pedal Control Signal 1 | PWM / Frequency Input 8 |
| 73 | Quick Coupler Safety | On/Off Sourcing Driver 4 |
| 77 | Key Switch Start | Switch to Battery Input 1 |
| 78 | A/C Pressure Switches | Switch to Battery Input 2 |
| 79 | Hydraulic Lockout | Switch to Battery Input 3 |
| 80 | VAB/AUX/POB Pedal Control Signal 2 | PWM / Frequency Input 9 |
| 81 | Battery - | Battery - |
| 82 | Battery - | Battery - |
| 83 | Battery - | Battery - |
| 84 | Battery + | Battery + |
| 85 | Battery + | Battery + |
| 86 | Battery + | Battery + |
| Contact Description for Connector J2 | ||
|---|---|---|
| No. | Function | Type |
| 2 | Aux 1 Supply A | PWM Driver 17 |
| 3 | Travel Right FWD | PWM Driver 6 |
| 4 | Travel Right Rev | PWM Driver 7 |
| 5 | Travel Left FWD | PWM Driver 8 |
| 6 | Travel Left Rev | PWM Driver 9 |
| 8 | Aux 1 Return B | PWM Driver 18 |
| 10 | Air Temperature Sensor | Return |
| 11 | Blade Solenoid | Return |
| 12 | Swing Brake Unlock Solenoid | Driver Low Side Return |
| 13 | Blade Raise | PWM Driver 10 |
| 14 | AUX / Boom Solenoid | Return |
| 16 | Boom Swing Left | PWM Driver 19 |
| 19 | AUX 2 Relay | Return |
| 21 | Blower Motor Control | Sinking Driver 9 |
| 22 | Water Valve Control | Sinking Driver 10 |
| 23 | CAN A+ | CAN A High |
| 24 | Boom Swing Right | PWM Driver 20 |
| 25 | Blade Lower | PWM Driver 11 |
| 26 | Travel LH/RH Solenoid | Return |
| 28 | Engine Speed Sensor - | Sensor Input 2+ |
| 29 | Left Travel Pedal Signal 1 | PWM / Frequency Input 10 |
| 31 | CAN A - | CAN A Low |
| 33 | Bypass | PWM Driver 12 |
| 34 | VAB Raise | PWM Driver 21 |
| 36 | Engine Speed Sensor + | Sensor Input 2+ |
| 37 | Left Travel Pedal Signal 2 | PWM / Frequency Input 11 |
| 38 | Right Travel Pedal Signal 1 | PWM / Frequency Input 12 |
| 39 | Calibration Pressor Sensor | PWM / Frequency Input 21 |
| 41 | VAB Lower | PWM Driver 22 |
| 43 | Right Travel Pedal Signal 2 | PWM / Frequency Input 13 |
| 44 | Main Hydraulic Pump Pressure Sensor | PWM / Frequency Input 14 |
| 45 | Blade Lever - Travel Speed Select | Switch to Ground Input 19 |
| 46 | Boom HE Pressure Sensor | PWM / Frequency Input 15 |
| 50 | Boom RE Pressure Sensor | PWM / Frequency Input 16 |
| 67 | Barometric Pressure Sensor | Active Analog Input 5 |
| 69 | Engine Coolant Temperature Sensor | Passive Analog Input 3 |
| 70 | Blade Expand Switch | Switch to Ground Input 30 |
| 77 | HVAC AIR Temperature Sensor | Passive Analog Input 4 |