دائرة التحكم بالسخان مفتوحة أو مقصورة

The control circuit for a heating element open or shorted, so the module cannot switch it. It covers the control side rather than the heavy supply — the low-current signal that tells a relay or driver to energise, which is a different circuit from the one carrying the load.

Separating the two halves is the diagnosis. An open control circuit means the command never arrives; a shorted one may energise the heater permanently or trip the module's protection. A heater that is always on is as much a fault as one that never is, and the permanently-on case wastes power and can overheat the element.

Test at the relay's control terminals rather than at the load. A command present there with no relay operation is the relay; absent means the fault is upstream in the harness or the driver. These circuits are low-current, so corrosion matters more than it would on a supply — a joint that would carry ten amps happily can fail to switch a relay coil.