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.
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.
Illustration 1 is an example of the operating range of a sensor.
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| Illustration 1 | g01365757 |
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Example of the typical operating range of a sensor (1) This area represents the normal operating range of the engine parameter. (2) In these areas, the engine is operating in an unsafe operating range of the monitored parameter. An event code will be generated for the monitored parameter. The sensor circuit does not have an electronic problem. Refer to Troubleshooting, “Troubleshooting with an Event Code” for additional information on event codes. (3) In these areas, the signal from the sensor is outside of the operating range of the sensor. The sensor circuit has an electronic problem. A diagnostic code will be generated for the sensor circuit. |
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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.
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 code
This 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.
Some diagnostic codes may be easily triggered. Some diagnostic codes may log occurrences that did not result in complaints. The most likely cause of an intermittent problem is a faulty connection or damaged wiring. The next likely cause is a component failure. The least likely cause is the failure of an electronic module. Diagnostic codes that are logged repeatedly may indicate a problem that needs special investigation.
Note: Always clear logged diagnostic codes after investigating and correcting the problem which generated the code.