Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Flash Electrically Erasable Programmable Read Only Memory (EEPROM): Description
Flash electrically erasable programmable read only memory (EEPROM) is contained in an integrated circuit (IC) internal to the powertrain control module (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 carry out this procedure may generate diagnostic trouble code (DTC): P1639, VID Block not programmed or is corrupt. The VID block in an existing PCM can also be tailored to accommodate various hardware changes made to the vehicle since production. Failure to carry out this procedure properly may generate DTC: P1635, Tire/Axle Ratio out of Acceptable Range. 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, and the presence of speed control. Only items applicable to 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 VID block is also limited to the number of times to be reconfigured. When this limit is reached, the scan tool displays a message indicating the need to flash the PCM again to reset the VID block.
Reprogramming can be carried out by a local Ford dealer or any non-Ford facility. Refer to the manufacturer's user manual for details.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.