Diagnostic codes are used by the electronic system in order to alert the operator that a problem exists. A diagnostic code also indicates the nature of the problem to the service technician.
Diagnostic codes may be viewed by using the Caterpillar Electronic Technician (ET). The Component Identifier (CID) identifies a specific component in the system that is described by the diagnostic code. The Failure Mode Identifier (FMI) indicates the failure mode.
The code number will direct you to a procedure in Troubleshooting, "Troubleshooting With A Diagnostic Code". Do not confuse diagnostic codes with diagnostic events. Events can be logged in the Electronic Control Module (ECM). These events that are logged can be used in order to investigate the engine information. An example would be a low oil pressure event. An event is generated when the engine oil pressure is low but not out of the range for the sensor. This does not indicate a problem with the sensor. This event indicates a problem with the engine oil pressure.
An active diagnostic code represents a problem with the electronic control system. The cause of the diagnostic code should be corrected as soon as possible. When an active diagnostic code is generated, a diagnostic lamp will indicate the diagnostic code. If the condition that generates the diagnostic code occurs only for a brief moment, the message will disappear and the diagnostic code will be logged in the memory of the ECM.
When the ECM generates a diagnostic code, the ECM will log the code in the permanent memory of the ECM. The ECM has a diagnostic clock that is internal. This clock records the hour of the first occurrence, the hour of the last occurrence, and the number of occurrences of the code. Knowing the timing of the code and knowing the frequency of the code can be a valuable indicator. These indicators are helpful when problems that are intermittent are being investigated.
Note: Cat ET can be used in order to retrieve logged codes and Cat ET can be used in order to erase logged codes. Logged diagnostic codes will automatically be deleted if no additional occurrences are recorded in 100 hours. Be aware of the following information when logged diagnostic codes are investigated.
- Some diagnostic codes may log occurrences that did not result in operator complaints. A diagnostic code is logged at a specific time. This time should correlate to a complaint. A repair may not be necessary if there is no correlation.
- The most likely cause of an intermittent problem is a faulty connection or damaged wiring. The next most likely cause of an intermittent failure is a component failure such as a sensor or a switch. The least likely cause of an intermittent problem is a failure of the ECM.
- Diagnostic codes that are logged repeatedly may indicate a problem that needs special investigation.
- The code number will direct you to a procedure in troubleshooting guide. If the symptoms continue, use the proper procedure for troubleshooting the symptoms that have been experienced by the operator. Refer to Troubleshooting Without A Diagnostic Code.
Note: Always clear logged diagnostic codes after investigating and correcting the problem which generated the code.
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| Illustration 1 | g01040769 |
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Output voltage from a typical analog temperature sensor | |
Illustration 1 indicates the signal range for a typical analog sensor. Diagnostic codes will be generated if the output signal for the sensor is below 0.2 VDC or above 4.8 VDC.