Code 71 is for the regn current sensor.
The control card is seeing an open for the green wire that runs from the card to the regen sensor.

The sensor is very low current and voltage, so it's liley just a jiggly conection at the plug.
It's wire 21 at the small outside plug.
Simply unplugging it then plugging it in will likley fix it.

If not, you'll need an ohm-meter to test the wire and the sensor.
There should be ~0 ohms between wire 21 and wire 22 on the same plug.