SC543

What it means

Center thermistor saw ~240°C. Software over-temp. Can be a real runaway or a thermistor that fell onto the roller.

Likely causes

• Thermistor off its mount (reads the roller skin)
• PSU heater drive stuck on
• IOB / BICU control
• Triac shorted

1. 1UnplugDo not keep cycling power into a 543. Unplug and cool.
2. 2Thermistor mountIf the NC sensor dropped onto the roller it will read a runaway. Reseat or replace.
3. 3Stuck-on heaterIf the heater stays on with the thermistor correctly mounted, replace PSU then IOB. On older engines, BICU.
4. 4Reset only after repairSP5-810. A 543 that is reset without a parts change will come back and can damage the unit.

Parts to have on the truck

• Thermistor
• PSU
• IOB
• Fusing unit

Related procedures

• SC reset (SP5-810)

  Clear a latched Level A/B service call after the repair is actually done.

• Fusing unit replacement

  Swap the fuser on IM C / MP C without creating a 541/548 encore.

Related codes