Snapshot Mode

Description:
The PCM snapshot feature is designed to assist in diagnosis of intermittent or unrepeatable problems. When a PCM snapshot is taken, all or some of the PCM's data and input parameters from that moment in time are stored for retrieval through the on-board diagnostic system and use in diagnosing a problem. PCM snapshots are taken in three instances; when most codes are set, when Customer Snapshot is initiated, or when Take PCM Snapshot is commanded in on-board diagnostics.

All PCM snapshot data may be accessed through the PCM SNAPSHOT option in on-board diagnostics. The PCM snapshot selection is used for three things:

^ To record a snapshot while in diagnostics.
^ To retrieve snapshot data recorded while in on-board diagnostics or in the Customer Snapshot mode.
^ To retrieve PCM code snapshot data.

Customer Snapshot
The Northstar powertrain has an unique feature that allows a PCM snapshot to be recorded without being in on-board diagnostics by simply pressing two buttons on the CCDIC. This feature, called Customer Snapshot, records a complete set of PCM data parameters and inputs when the "OFF" and "FRONT DEFROST" buttons on the CCDIC are pressed simultaneously. Customer Snapshot only works when the vehicle is NOT in on-board diagnostics. This feature can be very useful when it is difficult to reproduce a condition. When this occurs, the owner or driver may be instructed to take a Customer Snapshot while the condition is present and return to the dealer for diagnosis when convenient.

A Customer Snapshot may be taken anytime the ignition is on and the vehicle is not in on-board diagnostics. While this is true, pressing the "OFF" and "FRONT DEFROST" buttons simultaneously for one second will cause a snapshot to be taken and the "SERVICE ENGINE SOON" MIL to be turned "ON" for 2 seconds as confirmation that a snapshot was taken.

This data may be retrieved by entering diagnostics, selecting PCM SNAPSHOT and viewing the PO01 SNAPSHOT (It will appear as a code snapshot with and code designation of PO01, hence the PO01 SNAPSHOT designation.) The Customer Snapshot data will be overwritten if another Customer Snapshot is taken or if a PCM snapshot is taken while in on-board diagnostics.

PCM Snapshot On Code Set
When a PCM code sets, the PCM does several things. Among them is to save useful data and input parameter information for service diagnosis. This information is referred to as "Snapshot on code set." You will see references to Snapshot on code set or snapshot data and input parameters in many PCM code trouble trees because this information can be useful in pinpointing a problem even if the problem is not present when the vehicle is in the service bay.

Snapshots on code set differ from customer snapshots and on-board diagnostic snapshots in that only a few relevant data parameters are saved with a code snapshot. For each code set, eleven data parameters and all twelve inputs are saved. Which eleven data parameters are saved varies based on the code set. Transaxle code snapshots generally contain transaxle related data parameters while fuel code snapshots generally contain fuel related data parameters. If several codes are set, snapshots for the three most recently set codes will be saved.

Snapshot on code set data may be retrieved through the PCM SNAPSHOT option. When PCM SNAPSHOT is selected, snapshots on code set will appear first in the order the codes were set, most recent first. Snapshots on code set appear as "PXXX SNAPSHOT" where "PXXX" is the PCM code number. When a "PXXX SNAPSHOT" is selected,

"PXXX DATA" will appear and if selected, will display data from immediately after the code was set. If "PXXX DATA" is not selected "PXXX INPUTS" will appear and if selected, will display input data from immediately after the code was set. Keep in mind that once "PXXX DATA" or "PXXX INPUTS" is selected, the parameter and input data displayed will look just like the normal PCM parameter and input data with the same parameter numbers except the parameters will not vary since it is displaying recorded data.

PCM Snapshot in On-Board Diagnostics
PCM snapshot data may also be taken and retrieved while in on-board diagnostic mode by selecting the PCM SNAPSHOT option. If no customer and PCM code snapshots are saved or if they are not selected, "TAKE PCM SNAPSHOT" will appear. Selecting "TAKE PCM SNAPSHOT" will record all data and input parameters. These parameters may then be viewed right away. This snapshot will only be saved while in on-board diagnostics. Exiting on-board diagnostics or turning the ignition "OFF" will erase a PCM snapshot taken while in diagnostics.

Important: Taking a PCM snapshot will erase any Customer Snapshot data previously stored.

After the snapshot is taken, "PCM SNAP DATA" will appear. Select "PCM SNAP DATA" to view saved data parameters. If "PCM SNAP DATA" is not selected, "PCM SNAP INPUTS" will appear. Select "PCM SNAP INPUTS" to view saved input parameters. Keep in mind that once

"PCM SNAP DATA" or "PCM SNAP INPUTS" is selected, the parameter and input data displayed will look just like the normal PCM parameter and input data with the same parameter numbers except it will not vary since it is displaying recorded data.

Diagnosing Intermittents Using PCM Snapshots
PCM snapshots may be very useful in diagnosing powertrain problems. Data stored through Customer Snapshot, while in on-board diagnostics, or when a PCM code was set may be retrieved and used to determine if a particular input was incorrect when the problem occurred. Many of the PCM code trouble trees will use Snapshot on code set information to pinpoint a problem if it is not current. For example, the trouble tree for code P028 uses the snapshot data parameter PD76 (gear ratio) to indicate what gear the transaxle was in when the code set. This information may be used along with the transaxle pressure switch indication to zero in on the circuit(s) that are intermittently shorted or open. Snapshot on code set data may even be used, as in code P023 trouble tree, to determine whether the engine was running or not. This is an important piece of data in diagnosing code P023.

In order to use Customer Snapshot data or PCM snapshot data that was recorded in on-board diagnostics, you must first understand what problem the driver was trying to capture in the snapshot. Once this is understood, any appropriate parameters may be retrieved and any abnormal parameter readings used to pinpoint what sensor or system is causing the problem. For example, say a vehicle comes in with an intermittent rough engine condition and a Customer Snapshot was taken while the engine was running rough. Several data parameters may be retrieved and an abnormal parameter noted. MAP sensor, ECT sensor, IAT sensor, and knock sensor parameters may be compared to normal values of those parameters and any values that are out of the normal range investigated. Also, the second digit of PCM output fault status B (PD17) may be retrieved. If it is a "1", the PCM noted a bad fuel injector circuit which may be causing the rough engine problem and should be investigated. While this method may result in increased diagnosis time, it also results in less actual repair time and fewer service comebacks.