Jenn-Air Cooktop Error Code U400

The U400 error code on a Jenn-Air cooktop indicates that the secondary voltage of the induction power unit has exceeded safe operating limits, specifically that the primary supply voltage is greater than 300 volts. The cooktop's control unit continuously monitors the incoming supply voltage, and when it detects a reading above this threshold, it triggers an automatic protective shutdown. This shutdown occurs within one second of detecting the overvoltage condition and is accompanied by a sustained audible tone, alerting the user that the unit has disabled itself to prevent internal component damage.

The root cause of U400 is almost always an incorrect mains voltage connection. Induction cooktops are precision-sensitive to supply voltage, and connecting a unit rated for a lower voltage supply to a higher voltage circuit will immediately trigger this fault. A common scenario involves a 208V or 240V cooktop being connected to an improperly wired circuit, or a unit being installed in a region or building with non-standard voltage. The control unit does not attempt to compensate for the overvoltage; it simply cuts power to the cooking zones and holds the error state.

Diagnosing U400 requires verifying the actual supply voltage at the cooktop's junction or terminal block using a calibrated multimeter before reconnection. The correct procedure is to disconnect power completely at the breaker, verify the circuit provides the correct mains voltage for the specific cooktop model, and ensure all wiring, panels, and components are fully reassembled before restoring power. No internal component replacement is typically needed if the voltage issue is corrected promptly, but prolonged exposure to overvoltage conditions can damage the power board.