am having to replace sensors alot firstly coolant now abs and soon emmissions so many sensors in these veichles is it econmical to keep running them

I assume you are not replacing these yourself, and that is the problem. The sensors are cheap, it is the labor rate that no one can afford.

Most ABS sensors last forever, there are no moving parts and no temperature extremes. Usually, the ABS sensor wires can get the insulation rubbed off or the sensor ring in the hub get so covered in brake dust that the sensor cannot detect movement anymore.

Is your mechanic a Volvo dealership? Most non-dealers do not have scanners that can read ABS specific faults and rely on generic codes which are just a guess.
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My name is Klaus and I am a V♂lv♂holic

"...so many sensors in these veichles is it econmical to keep running them..."

So you don't know if keeping the car makes any sensor not? :)

Sorry, couldn't resist.