Shared FEPS and flash code pin

On many ECUs, the flash code pin is shared with the FEPS pin. This causes some confusion, which we hope to clear up.

How is it possible to have a pin be both and input and an output?

When the ECU firmware first starts, the firmware configures that pin as an analog input so it can read the FEPS voltage. As soon as it's finished reading the FEPS voltage, the firmware immediately reconfigures that pin to be a low-side digital output.

So, what does that mean for using that pin?

The only important consideration is if you are using FEPS to enter reprogramming mode AND you want to check the flash code output. In this case, you must do the following:

1. Apply the FEPS voltage to the FEPS pin (as described on the FEPS help page).

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