PAD 3112713 - Caterpillar

Electronic Control Module (ECM) has the ability to detect problems with the electronic system and with engine operation. When a problem is detected, a code is generated. An alarm may also be generated. There are two types of codes:
Diagnostic
EventDiagnostic Code - When a problem with the electronic system is detected, the ECM generates a diagnostic code. This indicates the specific problem with the circuitry.Diagnostic codes can have two different states:
Active
LoggedActive CodeAn active diagnostic code indicates that an active problem has been detected. Active codes require immediate attention. Always service active codes prior to servicing logged codes.Logged CodeEvery generated code is stored in the permanent memory of the ECM. The codes are logged.Logged codes may not indicate that a repair is needed. The problem may have been temporary. The problem may have been resolved since the logging of the code. If the system is powered, it is possible to generate an active diagnostic code whenever a component is disconnected. When the component is reconnected, the code is no longer active. Logged codes may be useful to help troubleshoot intermittent problems. Logged codes can also be used to review the performance of the engine and of the electronic system.Event CodeAn event code is generated by the detection of an abnormal engine operating condition. For example, an event code will be generated if the oil pressure is too low. In this case, the event code indicates the symptom of a problem.