Three faults pointed in three directions.
The unit was running but would not respond to a cooling demand. The board showed alarms 184, 93, and 74. D33 was slow flashing, SBUS had three wires connected, and zone sensor A2 showed no data.
Separate the lead fault from the downstream alarms.
HVAC Hero identified alarms 74 and 93 as downstream symptoms. The missing wall-sensor input at P298-6/7 was the lead fault, not proof that the sump-temperature sensor needed replacement.
Ground should land at P298-6 and temperature at P298-7. Nothing was landed at P298.
Lennox Energence M3 control manual · p.12Verify the sensor while you are already there.
HVAC Hero gave the connector and expected readings needed to confirm the sump thermistor rather than replacing it on suspicion.
Meter across P263-1 → P263-2. Valid range: 30 °F to 150 °F.
Cooling restored on the same visit.
The SBUS issue was corrected on site. No sensor was swapped, no tech-support call was needed, and the job stayed a one-visit solve.