HUB GP 8U5922 - Caterpillar

Diagnostic Codes
The engines Electronic Control Module (ECM) can monitor the circuitry between the ECM and the engines components. The ECM can also monitor the engines operating conditions. If the ECM detects a problem, a code is generated. Only six codes can be displayed at one time. If more codes are generated, a displayed code must be cleared before an additional code can be displayed.There are two categories of codes:
Diagnostic code
Event codeDiagnostic Code - A diagnostic code indicates an electrical problem such as a short circuit or an open circuit in the engines wiring or in an electrical component. Diagnostic codes end with a Failure Mode Identifier (FMI) of 2, 3, 4, 5, 7, 8, 10, 12, 14, or 31.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 coolant temperature is too high. In this case, the event code indicates the symptom of a fault. Generally, event codes indicate abnormal operating conditions or mechanical problems rather than electrical problems. Event codes end with a Failure Mode Identifier (FMI) of 0, 1, 15, 16, 17, or 18.Codes can have two different states:
Active
LoggedActive Codes
An active code indicates that a fault is present. Service the active code first. For the appropriate troubleshooting procedure for a particular code, refer to Troubleshooting, "Diagnostic Trouble Codes".Logged Codes
The codes are logged and stored in the ECM memory. The fault may have been repaired and/or the fault may no longer exist. If the system is powered, an active code may be generated whenever a component is disconnected. If the component is reconnected, the code is no longer active but the code may become logged.Logged codes may not indicate that a repair is needed. The fault may have been temporary. Logged codes may be useful to help troubleshoot intermittent faults. Logged codes can also be used to review the performance of the engine and of the electronic system.