
RENR9348-01 49
Troubleshooting Section
Troubleshooti
ng with a
Diagnostic Code
i02432846
Diagnostic Codes
SMCS Code: 1900
Diagnostic Codes
Diagnostic codes alert the operator that a problem in
the electronic system has been detected. Diagnostic
codes also indicate the nature of the problem to
the service technician. The Caterpillar Electronic
Technician (ET) is a software program that is
designed to run on a personal computer. Diagnostic
codes may be viewed on a personal computer that
has Cat ET software. Diagnostic codes consist of
the component identifier (CID) and the failure mode
identifier (FMI).
Component Identifier (CID) – The CID is a number
with three or four digits. The CID indicates the
component that generated the code. For example,
the CID number 0001 identifies the fuel injector for
the number one cylinder.
Failure Mode Identifier (FMI) – The FMI is a two
digit code that indicates the type of failure.
Suspect Parameter Number (SPN) – The SPN is a
three digit code which is assigned to each component
in order to identify data via the data link to the ECM.
This is used on the diagnostics for the CAN data link.
Refer to Troubleshooting, “Diagnostic Code Cross
Reference” for the complete list of the diagnostic
codes and a description of each code. There is a
troubleshooting procedure for every diagnostic code.
Refer to Troubleshooting, “Troubleshooting With A
Diagnostic Code”.
When a diagnostic code is activated, the Electronic
Control Module (ECM) transmits information about
the code over the J1939 data link. Some J1939
devices may display the code. However, the code
will be displayed with a SPN-FMI code. Refer to
Troubleshooting, “Diagnostic Code Cross Reference”
for a cross-reference between SPN-FMI codes and
diagnostic codes.
Do not confuse diagnostic codes with event codes.
Event codes alert the operator that an abnormal
operating condition such as low oil pressure or high
coolant temperature has been detected. Refer to
Troubleshooting, “Troubleshooting with an Event
Code” for additional information on event codes.
g01117578
Illustration 7
Output voltage from a typical analog temper ature sensor
Illustration 7 indicates the signal range for a typical
analog sensor. Diagnostic codes will be generated if
the sensor’s output signal is below 0.2 VDC or above
4.8 VDC.
Active Diagnostic Codes
An active diagnostic code represents a problem with
the electronic control system. Correct the problem
as soon as possible.
When the ECM generates an active diagnostic code,
the “Active Alarm” indicator (“Engine Control Alarm
Status” on Cat ET) is activated in order to alert the
operator. If the condition that generated the code
is momentary, the message disappears from the
list of active diagnostic codes. The diagnostic code
becomes logged.