2008 1.6FSI electrical issue

So my girlfriend's car has gone batty.

She's got an intermittent fault where the fault codes say there's a low voltage issue coming from both channels of the throttle pedal, the throttle actuator and the oil temp/level sender.

The issue comes on when she's driven the car for a while and then comes to the end of her journey and always in an urban environment.

I've tried swapping throttle pedals (for my car) when the fault manifests and it didn't clear the issue.

We swapped the ECU over which seemed to have the car run better, but the fault came back after the first long drive.

Has anyone else come across this issue before? I think it could be a voltage supply issue to the ECU, but don't know whether the voltage control is done through the CAN BUS or whether there is a separate module that provides the 5V.

Any help is much appreciated