It's not uncommon for one or two fault codes to appear after an ECU calibration. Many are adaptation-related and clear themselves after a driving cycle. However, some indicate genuine issues that need attention.
Common post-remap codes that typically self-resolve: boost adaptation faults (the ECU is learning the new target pressures), lambda sensor adaptation (adjusting to new fuelling maps), and transmission adaptation faults (if torque limits have changed).
Codes that require investigation: persistent misfire codes, knock sensor faults, turbo underboost faults that don't clear, oil pressure warnings, and coolant temperature warnings. These may indicate a hardware issue that the new calibration is exposing, or in rare cases, a calibration parameter that needs adjustment.
Always report persistent fault codes to your calibration provider with the full code description and freeze frame data.