With the older GM ECMs the error codes are stored in memory for the last 50 engine start/run cycles. Once a fault has been repaired, the codes will erase after that occurs.
As for the quad driver outputs in the ECM, they are monitored for open circuits, shorted circuits, and voltages outside the allowable range. Those outputs operate things like the EVAP vent and purge solenoids, TCC lockup solenoid or other transmission shift solenoids, EGR vacuum solenoid, cooling fan relay, A/C clutch relay, and any other options. Shorted or open wiring, disconnected solenoids or relays, or solenoid/relay faults are common problems causing these codes.
Your factory wiring diagrams should indicate which loads are connected to QDM A (code 26) and QDM B (code 56).