What Does This Error Mean?

A Marlin temperature sensor error means the firmware is reading an impossible temperature from a thermistor — usually because the thermistor wires are broken or the wrong thermistor type is configured. Check the thermistor wiring connections at the hotend and heated bed.

Affected Models

Creality Ender series with Marlin
Prusa MK series with Marlin
Any Marlin-based FDM 3D printer

Common Causes

Broken or disconnected thermistor wires at the hotend or heated bed
Wrong thermistor type configured in Marlin Configuration.h (TEMP_SENSOR setting)
Thermistor physically damaged — cracked ceramic tip or burned bead
Loose thermistor connector at the printer's control board
Short circuit in the thermistor wiring harness

How to Fix It

Check thermistor wiring connections.

Power off the printer and inspect the thermistor cable at the hotend and control board ends. Ensure the JST or Dupont connector is fully seated and that no wires are broken near the strain relief. Gently tug each wire — a broken wire will pull out of its pin.
Verify the TEMP_SENSOR setting in Configuration.h.

Open Configuration.h in your Marlin firmware source and find the TEMP_SENSOR_0 line for the hotend and TEMP_SENSOR_BED for the heated bed. The value must match the thermistor model installed in your printer — using the wrong code causes wildly incorrect temperature readings. Common codes: 1 = 100k NTC, 5 = 100k ATC Semitec.
Measure thermistor resistance.

With the printer powered off and the thermistor connector unplugged from the board, use a multimeter set to resistance (Ohms). A healthy 100k NTC thermistor at room temperature reads approximately 100,000 Ohms. A reading of 0 (short) or OL (open circuit) confirms the thermistor is faulty.
Inspect the thermistor for physical damage.

Visually inspect the thermistor bead at the tip of the hotend — it should be a small glass or ceramic bead seated in the hotend block. A cracked bead, burned insulation, or missing bead causes a MAXTEMP or MINTEMP fault immediately. Replace a visibly damaged thermistor before any further testing.
Replace the thermistor.

Thermistors are inexpensive (under $5 for most common types) and wear items on FDM printers. Match the replacement to the original spec: bead diameter, wire length, and NTC value. After replacing, run a PID autotune (M303 command) to recalibrate the temperature controller for the new thermistor.

When to Call a Professional

If the wiring is intact and the correct thermistor type is configured but the error persists, replace the thermistor. Thermistors are inexpensive consumable parts available for all common hotend and bed configurations.