The engine’s Electronic Control Module (ECM) has the ability to monitor the circuitry between the ECM and the engine’s components. The ECM also has the ability to monitor the engine’s operating conditions. If the ECM detects a problem, a code is generated.
There are three categories of codes:
- Diagnostic code
- Event code
- Flash Code
Diagnostic Code – A diagnostic code indicates an electrical problem such as a short or an open in the engine’s 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 mechanical problems rather than electrical problems.
Flash Code – Diagnostics and events are reported via flash codes. When a diagnostic code or an event code becomes active, the specific condition is immediately reported to the operator through a series of flashes on the diagnostic lamp. By counting the flashes, a numeric representation of the diagnostic code or event code is revealed.
Codes can have two different states:
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”
Refer to the Troubleshooting, “Diagnostic Code Cross Reference” for information that relates to converting flash codes to the equivalent diagnostic code or to the equivalent event code.
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 If the component is reconnected, the code is no longer active but the code may become logged.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.