The engine Electronic Control Module (ECM) has the ability to monitor the circuitry between the ECM and the engine components. The ECM also has the ability to monitor the engine operating conditions. If the ECM detects a problem, a code is generated.
There are two categories of codes:
- Diagnostic code
- Event code
Diagnostic Code - A diagnostic code indicates an electrical problem such as a short circuit or an open circuit in the engine wiring or in an electrical component.
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 problem. Event codes indicate abnormal operating conditions or mechanical problems rather than electrical problems.
Codes can have two different states:
- Active
- Logged
Any active engine diagnostic code will prevent an active regeneration from happening. This includes a manual regeneration through Cat® ET. The following are three codes that are exceptions to this.
- 3701-15 DPF Status: High - Least Severe
- 3701-16 DPF Status: High - Moderate Severity
- 5236002-0 High Frequency Regeneration
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"
- Troubleshooting, "Event 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, it is possible to generate an active diagnostic code 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 If the component is reconnected, the code is no longer active but the code may become logged.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 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.
The logged diagnostic codes will not show the hour meter of the first and last occurrence. Some diagnostic codes will show the number of occurrences.
In order to clear any logged diagnostic codes, the engine must be OFF and the key switch in the ON position.
Note: Ensure the "All ECM" box in the lower right corner of ET is not checked. If it is checked, logged codes will not clear since the Machine ECM requires the engine to be running.