Cm870 overheating issue? Maybe

[Chamberpains]

You have a cm870. You can probably just cut and splice into the fan solenoid wiring and run a toggle switch to the dash to "break" or "open the solenoid circuit to get a manual override. It shouldn't throw a code. To test this, simply unplug the solenoid with key on and see if your fan engages without throwing a code. Volvo may be different and have some strange dash code.

Cm871 and newer throw a code doing this. They get around this problem by plumbing in a 2nd solenoid down stream or right after the factory solenoid and have it isolated to its own electrical circuit.

As far as your codes, I would clear them and see if they come back. They only happened 1-2 counts "times". They all could be a 1 time blip. I wouldn't throw a harness at the truck for those codes and counts alone.

Low coolant = low coolant - add coolant

Loss if power without key off = low voltage to ECM with the key on - probably low batteries while cranking or possibly bad power wire connection.

Multiplexing codes often follow low voltage cranks or dead or dieing batteries.