OAT troubleshooting

[TShort]

I've got dual AFS-3500 (non s) in the new -10.

The OAT is currently not reading anything - just shows "--"

I'm going to pull the units today to replace the button batteries. Perhaps the batteries being dead is affecting the OAT since the unit won't hold certain settings or preferences.

Is there anything else I should do while the screens are out in order to troubleshoot? If I can get a meter on the pins for the OAT wires, what should I look for? I have no idea what the failure modes or normal readings for a functioning probe should be.

Thanks in advance.

Thomas