Bosch dryer displays E04 and may stop heating or shut down mid-cycle.

Safety first: Disconnect power before accessing internal components.

• Clean moisture sensor bars: Locate the two metal strips inside the drum (usually near the lint filter opening). Clean them thoroughly with a soft cloth and rubbing alcohol to remove fabric softener and detergent residue.
• Check for physical damage: Inspect the sensor bars for cracks or looseness. Tighten mounting screws if loose.
• Inspect wiring: Access the area behind the sensor bars (front panel removal may be required). Ensure the sensor wires are firmly connected and not broken.
• Test sensor continuity: Use a multimeter to check continuity across the sensor circuit when a damp cloth bridges the bars. Replace the moisture sensor assembly if no change is detected.

If cleaning and sensor replacement do not resolve E04, the main control board may not be processing sensor signals correctly and may need professional diagnosis.