Bosch Washer Error Code d:06

The d:06 error code on a Bosch washer indicates a fault within the NTC (Negative Temperature Coefficient) thermistor circuit combined with a relay failure condition. Specifically, the control board has detected that either the NTC sensor is reporting an excessively high temperature beyond its expected operating range, or the heating relay has become stuck in the closed position, continuously energizing the heating element even when the control system has not commanded it. Both conditions present a similar symptom profile because a stuck relay produces uncontrolled heating, which can then cause the NTC to read abnormally high values.

The NTC thermistor is a resistive temperature sensor whose resistance decreases as temperature rises. Under normal operation, the control board monitors this resistance to regulate wash and rinse water temperatures. When the NTC reads a temperature that exceeds acceptable thresholds, or when the resistance reading falls outside the expected range, the board interprets this as a thermal fault. Simultaneously, if the heating relay contacts weld together due to electrical arcing or age-related wear, current continues to flow to the heating element regardless of control board commands, creating a runaway heating scenario that compounds the error.

The first recommended diagnostic step is to run test P4, which exercises the heating circuit and allows a technician to evaluate both the NTC response and relay switching behavior in a controlled sequence. During this test, the technician can monitor whether the relay properly opens and closes and whether the NTC resistance values track correctly with temperature changes. Identifying whether the root cause is the sensor alone, the relay alone, or a combination of both is critical before ordering replacement components.