Flash Electrically Erasable Programmable Read Only Memory (EEPROM): Description

The flash EEPROM is contained in an integrated circuit internal to the PCM. The flash EEPROM contains the vehicle strategy including calibration information specific to the vehicle, and is capable of being programmed or flashed repeatedly.

As part of the calibration there is an area referred to as the vehicle identification (VID) block. The VID block is programmed when installing a new PCM as described under Programming the VID Block for a Replacement PCM. Failure to carry out this procedure may generate DTC P1635 or P1639. The VID block in an existing PCM can also be programmed to accommodate various hardware or parameter changes made to the vehicle since production. Failure to carry out this procedure correctly may generate DTC P1635, Tire or Axle Ratio out of Acceptable Range. An incorrect tire or axle ratio is one of the main causes for DTC P1635. This is described under Making Changes to the VID Block and also under Making Changes to the PCM Calibration. The VID block contains many items used by the strategy for a variety of functions. Some of these items include the vehicle identification number (VIN), octane adjust, fuel octane, fuel type, vehicle speed limit, tire size, axle ratio, the presence of speed control, and 4 wheel drive electronic shift on the fly (ESOF) versus manual shift on the fly (MSOF). Only items applicable to the vehicle hardware and supported by the VID block are displayed on the scan tool.

When changing items in the VID block, the strategy places range limits on certain items such as tire and axle ratio. The number of times the VID block may be reconfigured is limited. When this limit is reached, the scan tool displays a message indicating the need to flash the PCM again to reset the VID block.

Some vehicles must have the engine serial number programmed. The DTC P264F Engine Serial Number Not Programmed Or Incompatible may set if the procedure is not carried out.

On vehicles equipped with permanent DTC reporting capabilities, neutral profile correction should be learned after a PCM replacement in order to activate the misfire monitor. This is accomplished using the Misfire Monitor Neutral Profile Learn function on the scan tool. Refer to the scan tool manufacturer's instruction manual for details.