Module Identifier (MID) - The MID is a code with two or three digits that indicates the electronic module which generated the diagnostic code. The MID for the Electronic Control Module (ECM) is 36. The MID for the Integrated Temperature Sensing Module (ITSM) is 111. Some electronic displays do not display the MID because the module which generates the code is obvious.
Component Identifier (CID) - The CID is a number with three or four digits. The CID indicates the component that generated the code. For example, the CID number 0017 identifies the fuel shutoff valve.
Failure Mode Identifier (FMI) - The FMI is a two digit code that indicates the type of failure. Table 1 is a list of the failure mode identifiers that are adapted from the "SAE J1587" standard.
| Failure Mode Identifiers | |
|---|---|
| FMI | Description of Failure |
| 00 | "Data valid but above normal operating range" |
| 01 | "Data valid but below normal operating range" |
| 02 | "Data erratic, intermittent or incorrect" |
| 03 | "Voltage above normal or shorted high" |
| 04 | "Voltage below normal or shorted low" |
| 05 | "Current below normal or open circuit" |
| 06 | "Current above normal or grounded circuit" |
| 07 | "Mechanical system not responding properly" |
| 08 | "Abnormal frequency, pulse, or period" |
| 09 | "Abnormal update" |
| 10 | "Abnormal rate of change" |
| 11 | "Failure mode not identifiable" |
| 12 | "Bad device or component" |
| 13 | "Out of calibration" |
| 14 | "Not used" |
| 15 | "Not used" |
| 16 | "Parameter not available" |
| 17 | "Module not responding" |
| 18 | "Sensor supply fault" |
| 19 | "Condition not met" |
| 20 | "Not used" |
Note: Do not confuse diagnostic codes with event codes. For information on event codes, see Troubleshooting, "Troubleshooting with an Event Code".
Illustration 1 represents the operating range of an oil temperature sensor. The diagram is a reference. Do not use the diagram to troubleshoot the oil temperature sensor.
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| Illustration 1 | g00791619 |
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Typical operating range of an oil temperature sensor (1) In these areas, the output voltage of the sensor is too high or too low. The output is outside of the normal range. The electronic problem will generate a diagnostic code. (2) In this area, the oil temperature above (3) This area represents the normal operating temperature for the engine oil. The normal output voltage of the sensor is between 0.2 and 4.1 volts. | |
An active diagnostic code represents a problem with the electronic control system. Correct the problem as soon as possible.
When an active diagnostic code is generated, the "Active Alarm" indicator ("Engine Control Alarm Status" on Cat ET) is activated in order to alert the operator. If the condition that generated the code is momentary, the message disappears from the list of active diagnostic codes. The diagnostic code becomes logged.
When an ECM generates a diagnostic code, the ECM logs the code in permanent memory. Each ECM has an internal diagnostic clock. Each ECM will record the following information when a code is generated:
- The hour of the first occurrence of the code
- The hour of the last occurrence of the code
- The number of occurrences of the code
This information is a valuable indicator for troubleshooting intermittent problems.
A code is cleared from memory when one of the following conditions occur:
- The service technician manually clears the code.
- The code does not recur for 1000 hours.
- A new code is logged and there are already ten codes in memory. In this case, the oldest code is cleared.
Some diagnostic codes may be easily triggered. Some diagnostic codes may log occurrences that did not result in complaints. The most likely cause of an intermittent problem is a faulty connection or damaged wiring. The next likely cause is a component failure. The least likely cause is the failure of an electronic module. Diagnostic codes that are logged repeatedly may indicate a problem that needs special investigation.
Note: Always clear logged diagnostic codes after investigating and correcting the problem which generated the code.