.. _shared_feps_and_flash_pin:

Shared FEPS and Flash Code Pin
==============================

On many ECUs, the flash code pin is shared with the FEPS. This section aims to
clarify the confusion surrounding this.

How is it Possible for a Pin to be Both an Input and an Output?
---------------------------------------------------------------

When the ECU firmware initially boots up, it configures the pin as an analog
input to read the FEPS voltage. After reading the FEPS voltage, the firmware
immediately reconfigures the pin as a low-side digital output.

So, What Does that Mean for Using that Pin?
-------------------------------------------

If you are using FEPS to enter reprogramming mode *and* you want to check the
Flash Code Output then you must:

1. Apply the FEPS voltage to the FEPS pin.
2. Cycle power to your ECU.
3. Remove the voltage source from the FEPS pin and then connect your LED to
   the same pin to read the flash code.