Storing and Erasing Freeze Frame Data

STORING AND ERASING FREEZE FRAME DATA
(This article explains what freeze frame data is, when and what operating conditions are stored, who has priority over freeze frame data, and when freeze frame data may be erased.)

Each time a diagnostic test reports a fail, the current engine operating conditions are recorded. A subsequent failure will update the recorded operating conditions. The recorded operating conditions vary depending on the diagnostic test which failed but typically include:

^ Air fuel ratio.
^ Air flow rate.
^ Fuel trim.
^ Engine speed.
^ Engine load.
^ Engine coolant temperature.
^ Vehicle speed.

Government regulations require engine operating conditions to be captured whenever the Malfunction Indicator Lamp (MIL) is turned "ON." The data captured is called freeze frame data. The freeze frame is very similar to a single record of operating conditions. Whenever the MIL is illuminated, the corresponding record of operating conditions is copied to the freeze frame.

Freeze frame data can only he overwritten with data associated with a misfire or fuel system malfunction. Data from these systems take precedence over data associated with any other fault.

The freeze frame data will not be erased unless the history Diagnostic Trouble Code (DTC) is cleared for the malfunction recorded in freeze frame.

FAILURE RECORDS BUFFER
To get more complete information on the status of the vehicle, the technician may view the stored parameters found in the failure records buffer. The same information that is stored in the freeze frame is also found in the failure records buffer with one exception that benefits the technician. Instead of just one freeze frame, the failure record buffer has the ability to store up to as many as five different buffers of information for five individual DTCs. This information can be much more beneficial to the technician in attempting to repair a vehicle which has multiple codes set.

The freeze frame data is updated only once when the first emission related history DTC is stored and the MIL is turned "ON."

For the failure records buffer, the information contained within is updated each time a diagnostic test reports a failure. This function ensures that the technician will be working with the latest information that was available prior to repair of the vehicle.

During normal operation, freeze frame and failure records buffer information will clear anytime the associated history DTC is cleared from memory.