795F AC Off-Highway Truck : Electronic Control Module (Drive Train)

Location of the Drivetrain ECM in the cab front ECM compartment (1) Drivetrain ECM (2) J2 harness connector (3) J1 harness connector (4) Chassis ECM(5) Brake ECM

ECM Connectors and Contacts

Electronic control of the Electric Drive Train System is provided by three Electronic Control Modules (ECM). The three electronic controls are the Drivetrain ECM, the Motor 1 ECM and the Motor 2 ECM.

The Drivetrain ECM is the primary control module in the system. The operation of the two motor control modules will be enabled or disabled by the Drivetrain ECM. The Motor 1 ECM and the Motor 2 ECM receive operational commands from the Drivetrain ECM. The motor control ECMs will then control the operation of the left-hand and the right-hand traction motors according to the commands.

The Drivetrain ECM is a standard A4:M1 model electronic control module. This model ECM is used for machine system control on many of the machines that are in the Caterpillar product line.

While the three control modules look physically the same, the Motor 1 ECM and the Motor 2 ECM are A4:P1 model electronic control modules. The A4:P1 control modules are equipped with different input circuit assignments and different output circuit assignments when compared to the Drivetrain ECM A4:M1.

For more information on the Motor 1 ECM and the Motor 2 ECM, refer to the Systems Operation, "Electronic Control Module (Motor)" section of this manual.

ECM Pull Up Voltage

In order to aid in diagnostics of certain types of electrical circuits that are controlled by the ECM, an internal "pull up resistor" is connected between many ECM l input circuits and an above normal voltage source.

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 voltage to be pulled high through the ECM pull up resistor. The result will be 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

The ECM pull up resistor voltage should always be considered when troubleshooting one of the circuit types that are listed.

ECM Pull Down Voltage

In order to aid in diagnostics of some of the electrical circuits that are controlled by the ECM, an internal "pull down resistor" is connected between the ECM switch to battery type input circuits and an ECM ground circuit.

During normal operation, the closed switch contacts that are connected to a voltage source will hold the circuit high. When circuit conditions such as open switch contacts, 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 to ground potential through the ECM pull down resistor. The result will be 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 ECM pull down resistor should always be considered when troubleshooting a switch to battery type of input circuit.

Inputs

The machine has several different types of input devices. The ECM receives machine status information from the input devices. Based on the inputs, the ECM 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 a voltage 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.

Outputs

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.

Input/Output

Electronic communication between the Drivetrain ECM, the Motor 1 ECM, the Motor 2 ECM is conducted over the CAN B Data Link system and the J1939 CAN A Data Link system. In addition, the Drivetrain ECM will communicate with other machine control modules using the Cat Data Link system.

The data link circuits allow the sharing of information with other electronic control modules. The data link circuits are bidirectional. The data link circuit will allow each ECM to send information and to receive information.

The CAN Data Link circuits are used for faster operational communication between the control modules on the machine. The Cat Data Link is used for some of the internal communication that does not require the faster speeds and is used for communication with external devices such as the Caterpillar Electronic Technician (Cat ET) service tool.

ECM Circuit Connections

A module identifier (MID) is assigned to the control modules on the machine. The MID is used to identify which ECM on the machine has activated a diagnostic code or an event code.

The MID for the Drivetrain ECM:

Drivetrain ECM - MID 081 (The ECM Location code is 3)

The following table provides a list of the machine wiring harness circuit connections for the Drivetrain ECM.

Note: ECM connector contact connections that are not listed are not used for this application.

Table 1

Drivetrain ECM - J1 Contact Connections MID 081
No. (1)	Function	Type
1	Key Switch On	Key Switch Input
2	Engine Speed Sensor (+)	Frequency Input
3	Engine Speed Sensor (-)	Frequency Input
5	Motor 1 Speed Sensor 2 Signal A	Frequency Input
7	Motor 1 Speed Sensor 2 Signal B	Frequency Input
8	Electric Drive Cooling Fan Speed Sensor (+)	Frequency Input
9	Electric Drive Cooling Fan Speed Sensor (-)	Frequency Input
10	Cat Data Link (+)	Input/Output
11	5 Volt Sensor Supply to EFR	Sensor Supply
12	EFR Enable	ON/OFF Output
13	(-) Battery	System Power
16	Right Hand Motor Speed Sensor 2 Signal A	Frequency Input
18	Motor 2 Speed Sensor 2 Signal B	Frequency Input
19	CAN Shield - EFR circuit shield	CAN Shield
20	Cat Data Link -	Input/Output
21	Generator Temperature Sensor Return	Return (ECM Ground)
22	Generator Drive End Bearing Temperature Sensor	Passive Analog Input
23	(-) Battery	System Power
26	Location Code 0	Ground Input
27	Location Code 1	Ground Input
28	Location Code 2 - No connection	Ground Input
29	Generator Stator Temperature Sensor 1	Analog Input
30	Generator Stator Temperature Sensor 1	Analog Input
31	Battery +	System Power
32	Location Code Enable	Ground Input
38	Battery (+)	System Power
39	Battery (+)	System Power
44	8 Volt Sensor Power Supply to Throttle Pedal Position Sensor	Sensor Power
45	8 Volt Sensor Power Return to Throttle Pedal Position Sensor	Return (ECM Ground)
48	Electric Drive Cooling Fan Driver	PWM Proportional Output
50	Electric Drive Cooling Fan Return	PWM Return
53	Generator Non Drive End Bearing Temperature Sensor	Passive Analog Input
55	EFR Return	PWM Return
57	(-) Battery	System Power
60	EFR Return	PWM Return
63	Motor 2 ECM Enable	Switch to Ground Input
64	Motor 1 ECM Enable	Switch to Ground Input
69	10 Volt Sensor Power Supply	Sensor Power
70	10 Volt Sensor Return	ECM Ground

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The connector contacts that are not listed are not used. The connector has 70 contacts.

Table 2

Drivetrain ECM - J2 Contact Connections MID 081
No. (1)	Function	Type
4	EFR Circuit Return	ECM Ground
8	EFR Circuit Return	ECM Ground
9	Motor 1 ECM Enable	Sinking Driver Output
10	Motor 2 ECM Enable	Sinking Driver Output
16	Steer Cylinder Position Sensor	PWM Input
17	(+) DC Power Bus Voltage Status Signal 1	PWM Input
18	(+) DC Power Bus Voltage Status Signal 2	PWM Input
21	EFR Current Control Command	Sinking Driver Output
22	(-) DC Power Bus Voltage Status Signal 1	ECM Ground
24	Requested Gear Command from Chassis ECM	PWM Input
28	Redundant DC Power Bus Voltage Status Signal 1	PWM Input
29	Redundant DC Power Bus Voltage Status Signal 2	PWM Input
31	Throttle Lock Switch	Switch to ground input
32	Throttle Pedal Position Sensor	PWM Input
34	EFR Diagnostic Feedback	PWM Input
40	Left Front Wheel Speed Sensor Signal A	Frequency / PWM Input
41	Left Front Wheel Speed Sensor Signal B	Frequency / PWM Input
42	Right Hand Front Wheel Speed Sensor Signal A	Frequency / PWM Input
43	Right Front Wheel Speed Sensor Signal B	Frequency / PWM Input
56	J1939 CAN A (+)	Input/Output Communication (+)
57	J1939 CAN A Shield	CAN Shield
63	(-) DC Power Bus Voltage Status Signal 2	ECM Ground
64	CAN B Data Link (+)	Input/Output Communication
65	CAN B Data Link (-)	Input/Output Communication
66	CAN B Shield	CAN Shield
67	J1939 CAN A (+)	Input/Output Communication (+)
68	J1939 CAN A (-)	Input/Output Communication (-)
69	J1939 CAN A Shield	CAN Shield
70	J1939 CAN A Shield	CAN Shield

( 1 )

The connector contacts that are not listed are not used. The connector has 70 contacts.

MARYGAR