UM AX032200 Version 1.0 12-46
1.5. Miscellaneous
The Miscellaneous function block contains various parameters that affect the general diagnostic
performance of the ECU.
The
Undervoltage Threshold
,
Overvoltage Threshold
setpoints are used to set the limits for
when their respective diagnostic messages are triggered.
The
Current, Frequency, RPM
and
PWM Hysteresis
parameters are used to set the hysteresis
values that affect when an input/output fault can be cleared.
Lastly, the
CAN Diagnostic Setting
parameter is used to control all diagnostics with one general
setting. This can be used to disable diagnostics entirely, only transmit messages without a blank
SPN, or transmit diagnostic messages normally.
1.6. Diagnostics
The Diagnostic function block includes faults, each representing a diagnostic message that the
ECU can produce. Each Digital Output has a set of accompanying faults, all six outputs have an
Open Circuit, Short To VCC, and Short To Ground fault. While the two low-sourced outputs have
an additional Overcurrent fault. The remaining faults cover VPS Overvoltage and Undervoltage,
Overtemperature, and other faults.
If and only if the
Event Generates a DTC in DM1
parameter is set to true will the other setpoints in
the function block be enabled. They are all related to the data that is sent to the J1939 network as
part of the DM1 message, Active Diagnostic Trouble Codes.
A Diagnostic Trouble Code (DTC) is defined by the J1939 standard as a 4-byte value which is a
combination of:
SPN
Suspect Parameter Number
(first 19 bits of the DTC, LSB first)
FMI
Failure Mode Identifier
(next 5 bits of the DTC)
CM
Conversion Method
(1 bit, always set to 0)
OC
Occurrence Count
(7 bits, number of times the fault has happened)
In addition to supporting the DM1 message, the Controller also supports
DM2
Previously Active Diagnostic Trouble Codes
Sent only on request
DM3
Diagnostic Data Clear/Reset of Previously Active DTCs
Done only on request
DM11
Diagnostic Data Clear/Reset for Active DTCs
Done only on request
So long as even one Diagnostic function block has
Event Generates a DTC in DM1
set to true,
the Controller will send the DM1 message every one second, regardless of whether there are any
active faults, as recommended by the standard. While there are no active DTCs, the Controller will
send the “No Active Faults” message. If a previously active DTC becomes inactive, a DM1 will be
sent immediately to reflect this. As soon as the last active DTC goes inactive, it will send a DM1
indicating that there are no more active DTCs.
If there is more than on active DTC at any given time, the regular DM1 message will be sent using
a multipacket Broadcast Announce Message (BAM). If the controller receives a request for a DM1
