Several things come to mind;
1) Car 2 is not on “test mode”? Small toggle switch on I think the first card on the rack. Compare position to Car 1.
2) Placing Car 1 on test mode, what does Car 2 do?
3) Does your buddy have a PCD or World Tool to see inputs?
4) IIRC, there’s an LED for HRV (Hall Riser Voltage) output, Meaning when lit, this car available to answer hall calls. Might be above or below that little toggle switch.
Short of these, the PCD or World Tool is a must for these beauties.