Current (Hard) Code VS. History Code
PCM DIAGNOSTIC CODESThe "SERVICE ENGINE SOON" telltale or "SERVICE VEHICLE SOON" telltale on the Driver Information Center (DIC) usually means that a Trouble Code has been stored in the long term memory of the PCM.
CURRENT CODE
When the PCM determines that the test conditions and failure conditions for a particular code are true, it sets that code as "Current". All codes remain current at least until the next time the PCM finds the test conditions are true and the failure conditions are false. A few codes remain current until the next ignition cycle or until the failure conditions are false several times. These details are given on the facing page of the code trouble tree.
HISTORY CODE
After a code has been set, the PCM continues to monitor for the test and failure conditions. For most codes, if the test conditions are true and the failure conditions are false, the code is changed to history. Some codes require the test conditions to be true and the failure conditions false several times or require an ignition cycle to change from current to history. If there are no current codes for a period of 50 ignition cycles, all history codes will be cleared.
DIAGNOSTIC CODE DISPLAY
To display the diagnostic codes: The ignition must be in the "ON" position or the engine running and the Cruise Control ON/OFF switch in the "ON" position. The OFF and WARMER buttons of the Electronic Climate Control (ECC) are depressed until all the segments of the display are "ON". The Fuel Data Center will display the diagnostic codes in the following manner:
1. If there are any History Codes stored in the memory, they will be displayed first. The Fuel Data Center (FDC) will display . .E for 1 second followed by each of the Trouble Codes for 2 seconds.
2. If there are any Current Codes the FDC will display .E.E for 1 second followed by each Trouble Code for 2 seconds.
3. The same sequence will follow for the BCM codes. The letter ..F and .F.F will appear for the History and Current Codes.
4. After all of the Trouble Codes have been displayed the FDC will display .7.0. This indicates that the system is ready to perform diagnostic functions.