SEAL-O-RING 8M5253 - Caterpillar

The Electronic Control Module (ECM) has the ability to detect faults in the electronic system and with engine operation. A self-diagnostic check is also performed whenever power is applied to the ECM.When a fault is detected, a code is generated. An alarm may also be generated. There are two types of codes:
Diagnostic codes
Event codesDiagnostic Code - When a fault in the electronic system is detected, the ECM generates a diagnostic code. This indicates the specific fault in the circuitry.Diagnostic codes can have two different states:
Active
LoggedActive Code - An active diagnostic code indicates that an active fault has been detected by the control system. Active codes require immediate attention. Always service active codes prior to servicing logged codes.Logged Code - Every generated code is stored in the permanent memory of the ECM. The codes are logged for 100 operating hours unless a code is cleared by use of the electronic service tool.Event Code - An 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 fault.Logged codes may not indicate that a repair is needed. The fault may have been temporary. The fault 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 When the component is reconnected, the code is no longer active.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 faults. Logged codes can also be used to review the performance of the engine and the electronic system.