98 kw w900 red "check fluids" light coming on and off

Some, don’t think that old, but some trucks give an annoying light or buzzer when washer fluid is low... Macks were bad about that

 

Well on my KW, 10 model, there’s a sensor inside the coolant tank itself, I had to change the whole tank, always showed Check engine, and dinging constantly.
I wouldn’t know about that old of one, I’m sure they haven’t changed much, all levels were full, but the sensor inside the tank itself was reading it as empty. $130 for new coolant plastic tank

 

Yes sometimes the dinging can be a false alarm on other occasions it is real, one time I had part of the fan belt let go and it torn off the coolant sensor causing the alarm to go off, on another occasion had the alarm go off for the coolant this time it was a real low coolant level kept driving as I had no where to stop or nothing to refill eventually the engine shut down light came on I though yep this is for real fortunately I was now close to a safe spot to pull over. Called out Cummins service team who proceeded to refill with about 9 litres of coolant or just under 3 gallons, so still had plenty of coolant in reserve, and there was no danger of the engine ceasing, anyway drove off again this time with Cummins service vehicle following behind in case I run out of coolant again, traveled about 40 km before the low coolant warning light came on again, refilled with more coolant Again got mobile with Cummins following behind pulled up at the truck rest area on the new bi- pass this time no warning lights so no top up, told Cummins it was ok and they were free to go, then drove back to base, never found out where the leak was coming from, but it was losing at least 2 gallons of coolant every 60 km.

 

Pretty sure the only fluid it would monitor would be coolant level. And oil pressure, assume you have oil pressure gauge but ecm could read pressure from a different sensor, but if it wasn't reading any pressure it would give shut down most likely.
Probably coolant level