COUPLING 4M4054 - Caterpillar

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. 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 g01117578
Output voltage from a typical analog temperature sensor
Illustration 1 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 Electronic Control Module (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.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.