Brother Printer Error 42? Why There's More Than One Heat Code

If you've already looked into Brother's overheating error. Landed on error 40, error 42 might look like a duplicate or a typo.

It isn't. Brother uses several distinct numbers within the same general temperature-fault family.

The specific one you're seeing is genuinely useful information about where inside the machine the heat problem was detected.

What Error 42 Actually Means

Errors 40 and 42 through 44 all belong to the same overheating family on Brother printers. Each number corresponds to a reading from a different internal temperature sensor — the printer monitors heat at more than one physical point, typically around the fuser and nearby zones, rather than relying on a single sensor for the whole machine.

Error 42 specifically points to one of these particular monitored zones registering above its safe limit.

Why this matters:while the practical fix is largely the same regardless of which specific number in this family you're seeing, knowing there are multiple sensors involved explains why you might see 40 one time. 42 another on the same printer — it's not inconsistency, it's different sensors reporting on different occasions.

Fix 1: Stop and Let It Cool

Don't attempt to print again immediately. Leave the printer powered on and give it 15 to 30 minutes undisturbed to let internal temperature drop back into a normal range.

Why this works:this addresses the actual condition the error describes directly — genuinely elevated internal temperature —. It resolves on its own with time in the large majority of cases, since this is a protective pause rather than a hardware failure announcing itself.

Fix 2: Improve Airflow Around the Printer

Make sure the printer has clear space around its vents, isn't pushed tightly against a wall or inside an enclosed cabinet. Isn't sitting in direct sunlight or near another heat-generating device.

Why this works:restricted airflow makes it meaningfully easier for internal temperature to climb during normal operation. Improving ventilation around the unit reduces how often any of the codes in this temperature family show up in the first place.

Fix 3: Space Out Large Print Jobs

If error 42 tends to appear during long continuous printing sessions specifically, break large jobs into smaller batches with brief pauses between them.

Why this works: sustained printing is the most common trigger for any code in this family, since it's precisely when internal components are generating heat continuously with the least opportunity to dissipate it.

When to Call a Professional

If error 42 appears repeatedly during light, ordinary printing with good ventilation. No unusually large jobs involved, or persists well beyond a reasonable cooldown period, the specific sensor associated with this code may have a genuine fault rather than accurately reporting real heat. That's worth professional diagnosis.

Thermal Circuitry: How Error 42 Differs from Error 40 and Error 50

Brother laser and LED engines employ multiple negative temperature coefficient (NTC) thermistors to measure ambient chassis temperature as well as fuser roller heat. While Error 50 indicates a catastrophic fuser heater circuit breakdown and Error 40 represents excessive internal operating heat, Error 42 specifically signals that the internal temperature sensor detected an abnormal rate of temperature rise or a thermal fluctuation that exceeds safe operating parameters.

Step-by-Step Diagnostic & Reset Procedure

1. Check Room Ambient Temperature: If the printer is operating in an environment below 50°F (10°C) or above 90°F (32°C), the baseline resistance of the internal thermistor will be skewed, causing false Error 42 trips. Relocate the machine to a climate-controlled room.
2. Inspect the Exhaust Cooling Fan: On the side or rear of your Brother laser printer is a cooling fan. If dust bunnies or paper fragments have jammed the fan blades, heat builds up rapidly in the fuser chamber. Power down, blow compressed air through the fan grille, and verify the fan spins freely.
3. Cold Reset (Power Cycle with Capacitor Discharge):
   • Turn the printer power switch OFF.
   • Unplug the AC power cord from the wall outlet and from the rear of the machine.
   • Press and hold the physical Power button for 30 seconds while unplugged to drain the high-voltage capacitors on the power supply board.
   • Leave the printer disconnected for at least 20 minutes to allow the fuser thermistor to stabilize at true ambient temperature.
   • Plug directly into a dedicated wall outlet (avoid battery backup UPS units or surge protectors that can introduce voltage drops).
4. Inspect Fuser Thermistor Wiring: If comfortable opening the rear access panel, inspect the two-wire harness connecting the fuser unit to the low-voltage power supply. Check for pinched wires or scorched connectors.

Clearing Thermal Errors via Maintenance Mode

1. Enter Maintenance Moder/hardware-maintenance/brother-machine-error-maintenance-mode" title="Brother Maintenance Mode: How to Enter & What Error Codes Mean">Maintenance Mode: Power on while holding the Menu or Set button, or enter *2864 on keypad models.
2. Type 74 to view the thermal log.
3. Type 01 to reset NVRAM error counters.
4. Type 99 to exit and reboot .

Frequently Asked Questions