RELAY 5158199 - Caterpillar

Diagnostic Codes
The 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 diagnostic code is generated.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 the following troubleshooting procedure:
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 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 If the component is reconnected, the code is no longer active but the code may become logged.Logged diagnostic codes will be cleared from the "Logged Diagnostic Codes" screen on the electronic service tool when the code has not been active for 40 hours.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.