Any power source that is on when the engine is running will most likely also be on when the engine is not running (all circuits that are enabled with key in the ON position). The engine is only deemed running when RPM > 400 or so, in which the ECU would have to trigger some other system to enable a relay.
The EPS control unit receives the following signals across the CAN bus.
From the Dynamic Stability Control (DSC): - vehicle speed
From the Digital Engine Electronics (DME): - engine speed and status of terminal 15 (one message) - CAN status - status of Sport switch
From the steering-angle sensor (LWS): - steering-wheel angle - prefix of steering-wheel angle - status of steering-angle sensor (all signals in one message)
From the instrument cluster: - kilometre reading - switch day/night lighting (0=off, 1=on)
The instrument cluster receives the following signal from the EPS control unit across the CAN bus. - activation EPS indicator lamp in the instrument cluster (0=off, 1=on)
If you had a standalone ECU, this would be cake to implement.
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