The fixing film unit is not reaching its target temperature within the timeout window. After a fuser replacement this is most often a thermistor connector seated on the wrong pin row, or a film unit left with its shipping stopper in place.
Power down and unseat the fixing assembly. Check connector J4011 on the thermistor harness is fully home. Remove the orange shipping stopper if present. Clear the error in service mode: COPIER > FUNCTION > CLEAR > ERR, then power cycle.
FM1-B285-000 · FM1-A606-000