MAINTENANCE
6-16 / Electrical
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Command Zone™ Diagnostics
This computer software is used to connect a conventional laptop PC to the vehicle’s control module. The software
allows a mechanic to interrogate components within the multiplex system to determine the status of individual input
and output circuits.
Input/Output Sheets (I/O Sheets)
IMPORTANT: I/O sheets may be required to diagnose some multiplex related faults. These sheets should
be kept with the vehicle at all times. Replacement I/O sheets can be obtained by contacting
Pierce Manufacturing.
These vehicle-specific information sheets are generated during the design of a new vehicle and are invaluable for
troubleshooting. Due to the wide range of custom equipment found on Pierce apparatus, each electrical system is
designed for that specific application. I/O sheets provide instructions for the specific input and output locations for
each electrical circuit on the vehicle. Limited wiring diagram information is also included on the sheets.
Component LED Heartbeat (Red)
This is a blinking LED that is located on all multiplex modules. This LED blinks at the rate of one blink per second,
and indicates that the module is capable of communicating with other modules on the data link. Also a steady green
LED indicates B+ (battery) and ground to each module.
Input Module (Clear Case Option)
A label identifies the input corresponding to the LED. If the LED is on, the module is seeing an input from a device.
Input/Output Module (Clear Case Option)
A label identifies the input/output corresponding to the LED. If the LED is on, the module is seeing an input from a
device or the module output is active.
Output/Power Module (Clear Case Option)
A label identifies the output corresponding to the LED. If the LED is on, the module output is active.
Data Link Troubleshooting
The data link consists of three wires: two insulated wires and one shielding wire. The two insulated wires are called
“CAN L” and “CAN H.” CAN L is a green wire (Pin B); CAN H is a yellow wire (Pin A). Secondary locks are installed
on all data link connectors to prevent the data link from coming apart.
A 120 ohm terminating resistor plug is installed at each end of each J1939 data link. When the system is functioning
properly, the system will read 59-61 ohms across pins “A” and “B” of the data link connector. If this resistance is not
maintained, an intermittent system fail or communication lost message may appear on the CZIC.
An ohm reading of approximately 120 ohms indicates a terminating resistor that is missing, or a data link that is open
(loose connection). A 40-ohm reading indicates that an extra terminating resistor plug has been installed in the data
link.
Non-Command Zone™ Components
Never assume that the cause of the problem is the multiplex system. Check the device; it may be defective. Perform
all basic electrical checks (fuses, circuit breakers, wiring connections, terminals, etc.) before assuming the worst.
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