Mileage is stored in BCM, PCM, and DIC. If you replace a PCM, the mileage is tranferred from the BCM to PCM. Visa versa, but it does not change the mileage on the DIC. You should still be able to pull the correct mileage off the BCM or PCM. In an event where you replace the BCM, PCM, and DIC at the same time, you would then be SOL for correct mileage.