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

Flash Electrically Erasable Programmable Read Only Memory (EEPROM) is contained in an Integrated Circuit (IC) internal to the PCM. The EEPROM contains the vehicle strategy including calibration information specific to the vehicle and is capable of being reprogrammed or reflashed repeatedly.

As part of the calibration there is an area referred to as the Vehicle Identification (VID) block. The VID block must be programmed when replacing the PCM as described under Programming the VID Block for a Replacement PCM. Failure to perform this procedure may generate fault codes: P1635, P1639, VID Block not programmed or is corrupt. The VID block in an existing PCM can also be tailored to accommodate various hardware/parameter changes made to the vehicle since production. Failure to perform this procedure properly may generate fault code: P1635, Tire/Axle Ratio out of Acceptable Range is one of the main causes for code: P1639. 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 VIN number, octane adjust, fuel octane, fuel type, vehicle speed limit, tire size, axle ratio, the presence of speed control and four wheel drive electronic shift on the fly versus manual shift on the fly. Only items applicable to vehicle hardware and supported by the VID block will be displayed on the scan tool.

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

The following procedures use the Worldwide Diagnostic System (WDS) for reprogramming:

Reprogramming can be performed by a local Ford dealer for any non Ford facility. There are other Enhanced Scan Tools that may have reprogramming capabilities available. Refer to the manufacturers users manual for details.