3524B Engines for Off-Highway Trucks Caterpillar

The Electronic Control Module (ECM) has the ability to detect problems with the ECM inputs and outputs. When a problem is detected, a code is generated. An alarm may be present at the electronic display module. The diagnostic code is stored in the memory of the ECM.

There are two types of codes:

• Diagnostic Code

• Event Code

Diagnostic Code - When a problem with the electronic system is detected, the ECM generates a diagnostic code. The diagnostic code indicates electrical problems with the circuitry.

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 electronic problems.

Codes can have two different states:

• Active

• Logged

An active code indicates that a problem has been detected. The active code should be serviced first. Refer to the following sections:

• Troubleshooting, "Troubleshooting With A Diagnostic Code"

• Troubleshooting, "Event Codes"

The ECM also records Logged codes. Logged codes are stored in the ECM memory. A Logged code indicates that a problem was detected. The problem may have been repaired and/or the problem no longer exists.

Logged codes may not indicate that a repair is needed. The problem may have been temporary. The problem may have been resolved since the logging of the code. If the system is powered, it is possible to generate an active diagnostic code whenever a component is disconnected. When the component is reconnected, the code is no longer active. Logged codes may be useful to help troubleshoot intermittent problems. Logged codes can also be used to review the performance of the engine and the electronic system.