Is it safe to disconnect a sensor’s electrical connector while the engine is running, or when there is power to the circuit (ignition key ON)?
The Haynes Repair Manual instructions for testing the idle air control valve (iac) is to disconnect the wiring connector from the iac, while the engine is IDLING. Then, note any changes to the engine speed (rpm).
We know that breaking a circuit, when it’s energized, will produce voltage spikes. Electronic devices, such as the engine computer, can be damaged by voltage spikes.
Does the test procedure proposed, cause harmful amounts of voltage spikes?
It should be OK to disconnect while running. I believe the danger of a spike is when you reconnect. Turn it off when you reconnect.
Totally safe. For one, it’s only a 12v system, so there’s not much of a tendancy to arc in the first place. Secondly, the computer is designed to work in a fairly wide range of voltages, so any little voltage spike that did get produced wouldn’t bother it much.
The warning, for what it’s worth, applies to disconnecting the battery of a running car. There should be no problem disconnecting a single ultralow-wattage accessory. I’d do it with no concerns.