SPRING 8J6785 - Caterpillar

Diagnostic Codes
The Electronic Control Module (ECM) monitors the circuitry between the ECM and the engine components. The ECM also monitors the engine operating conditions. If the ECM detects a problem, a code is generated.There are two categories of codes:
Diagnostic trouble codes
Engine eventsDiagnostic Trouble Codes - A diagnostic trouble code indicates an electrical problem exists. The code can indicate that a short circuit or an open circuit in the engine wiring or in an electrical component exists.Engine Events - An engine event indicates the detection of an abnormal engine operating condition. For example, a diagnostic trouble code will be generated if the oil pressure is too low. In this case, the diagnostic trouble code indicates the symptom of a problem. Engine events indicate abnormal operating conditions or mechanical problems rather than electrical problems.Codes can have two different states:
Active
LoggedActive Codes
An active code indicates that a problem 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 problem may have been repaired and/or the problem may no longer exist. If the system is powered, an active diagnostic code will become active whenever a component is disconnected. If the component is reconnected, the code is no longer active, but the code will be logged.Logged codes may not indicate that a repair is needed. The problem may have been temporary. 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.