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When to Use a Snapshot
Use Snapshots ONLY to help determine engine/vehicle operating conditions when an intermittent problem occurs. If an intermittent diagnostic code is causing problems, use the snapshot data to determine if the problem seems to occur in specific engine rpm or vehicle speed ranges, coolant temperature ranges, etc. Use this data to attempt to duplicate these conditions with the vehicle and get the code to reoccur. DO NOT replace electronic components based on Snapshot data alone. The snapshot information is stored in frames every 0.24 seconds (if externally triggered) or every 0.48 seconds (if diagnostic code triggered). Frequently, the parameters are changing faster or slower than 0.24 seconds, the result will be a misdiagnosed problem if too much is interpreted from this information. Also, remember when viewing Diagnostic Triggered Snapshots, the ECM sets a sensor value with an ACTIVE Diagnostic Code to a default value when the code is Active. This is why the Sensor value suddenly jumps to a specific value at the trigger point and remains there for the rest of the snapshot frames. DO NOT attempt to interpret the information and analyze how the engine is operating from this historical information. Looking at this information under a "microscope" will lead to misdiagnoses because some parameters are not what are expected, even though they are completely unrelated to the problem under investigation.Diagnostic Code Triggered Snapshot
When a diagnostic code occurs the ECM records many of the status parameters available on the Caterpillar ET or ECAP Electronic Service Tools. The ECM records this information for 9.6 seconds before the code occurs, and 3.4 seconds after the code.External Triggered Snapshot
If desired, a snapshot can be externally triggered using either the Cruise Control Set/Resume Switch, or an Electronic Service Tool. By toggling the Cruise Control Set/Resume Switch quickly from Set to the Resume position, the ECM will take a snapshot of information. For the Electronic Technician (when available), the snapshot can be triggered from the Snapshot Recorder Tool (follow the instructions on the screen or help system). For the ECAP, the snapshot can be triggered from the Display/Trigger Snapshot screen, located under the Display Diagnostic Messages screen (follow the on screen instructions).Quick Stop Snapshot
For Personality Modules NOV95 or later a snapshot can also be stored for a Quick Stop occurrence if the Customer Parameter is programmed. The ECM stores the number of occurrences of the Quick Stop Event, as well as a snapshot of the latest occurrence.One data record is kept for the most recent Quick Stop occurrence activation. The record is stored with the most recent record replacing the previous record.Each Quick Stop record contains 60 frames of information; frame 45 is the Quick Stop occurrence, 44 frames before, 15 frames following the code. Each frame is separated by 1.0 second.Each frame of the snapshot record stores the following data: ECM Storage of Snapshots
The ECM can store up to six Diagnostic Code Triggered snapshots, four Externally triggered snapshots, and one Quick Stop Snapshot. They are stored in a "circular buffer", the newest snapshot will replace the oldest if a seventh Diagnostic Code Triggered snapshot or fifth Externally triggered snapshot is taken.The ECM stores the snapshots in memory maintained through the Unswitched (+)Battery connection. If the Unswitched (+)Battery connection is disconnected, or if the vehicle batteries are disconnected, the snapshot information is cleared.The snapshots can also be manually cleared using an Electronic Service Tool. Snapshots, like most Diagnostic Codes are automatically cleared by the ECM after 100 hours of operation.