LID 2721079 - Caterpillar

Diagnostic Codes
Diagnostic codes alert the operator that a problem in the electronic system has been detected. Diagnostic codes are also used by the service technician to identify the nature of the problem. Caterpillar Electronic Technician (ET) is a software program that is designed to run on a personal computer. The software can be used by the service technician in order to view the diagnostic code information for an ECM. Diagnostic codes may consist of the component identifier (CID), and the failure mode identifier (FMI).Component Identifier (CID) - The CID indicates the component that generated the code. For example, the CID number 1 identifies the fuel injector for the number one cylinder.Failure Mode Identifier (FMI) - The FMI indicates the type of failure.Refer to Table 1 for a complete list of the diagnostic codes and the appropriate troubleshooting procedure.Note: 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. If an event code is active, refer to Troubleshooting, "Event Code List".
Illustration 1 g01138880
Example of the typical operating range of a temperature sensor (1) This area represents the normal operating range of the parameter. The normal output voltage of the sensor is between 0.2 VDC and 4.2 VDC. (2) In this area, the temperature above 107 °C (225 °F) is higher than normal. The output voltage of the sensor will generate an event code. The sensor does not have an electronic problem. (3) In these areas, the output voltage of the sensor is too high or too low. The voltage is outside of the normal range. The electronic problem will generate a diagnostic code. Refer to Troubleshooting, "Diagnostic Trouble Code List" for additional information on diagnostic codes.Note: This graphic is an example. The signal ranges in this graphic are used only as examples.Active Diagnostic Codes
An active diagnostic code represents a problem with the electronic control system. Correct the problem as soon as possible.When the engine's 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.Logged Diagnostic Codes
When the ECM generates a diagnostic code, the ECM logs the code in permanent memory. The ECM has an internal diagnostic clock. Each ECM will record the following information when a code is generated:
The hour of the first occurrence of the code
The hour of the last occurrence of the code
The number of occurrences of the codeThis information is a valuable indicator for troubleshooting intermittent problems.A code is cleared from memory when one of the following conditions occur:
The service technician manually clears the code.
The code does not recur for 100 hours.
A new code is logged and there are already ten codes in memory. In this case, the oldest code is cleared.