Bosch Washer Error Code Er:05

Er:05 on a Bosch washer indicates that the NTC (Negative Temperature Coefficient) thermistor in the water heating circuit has been detected as open-circuited. The NTC thermistor is a temperature-sensing resistor responsible for reporting water temperature to the control board throughout the wash and rinse cycles. When the control board reads an open circuit from this sensor, it cannot verify water temperature and flags the fault to prevent overheating or incorrect cycle execution.

An open-circuit condition in the NTC circuit can result from two primary failure points: the thermistor itself or the wire harness connecting it to the control board. The thermistor can fail internally, losing continuity entirely, which produces the open-circuit reading. Alternatively, a wire harness that has been damaged by heat, pinched during installation, corroded at a connector, or broken internally can interrupt the signal path and produce the same fault code even if the NTC sensor itself is still functional.

Diagnosis should begin by running test P16, which exercises the NTC sensing circuit and allows you to confirm whether the fault is active and reproducible. After running the test, inspect the wire harness for visible damage, loose connectors, or corrosion at the terminals. Use a multimeter to check NTC resistance and verify continuity throughout the harness. A properly functioning NTC will show measurable resistance that changes with temperature, while an open-circuit reading of infinite resistance confirms thermistor failure.