DTC P1794 - Battery Supply Circuit Malfunction: Condition

WARNING: This page is about a different car, the 1997 Mazda Millenia. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when voltage at terminal No. 4B on Engine Control Module (ECM) harness connector is less than 1.4 volts (other than during starting). Possible causes are:

Battery malfunction.
Open or short circuit between terminal No. 4B on ECM and positive battery cable.
Open MAIN fuse.