This Topic has been covered before and I have done a lot of searching , so please go easy.
Does the expansion tank (a black one on TD6) have a replaceable tank sensor or is repairable by washing the tank, there are many thoughts on the latter suggestions , but all seem to be on clear tanks . The indicator is at the top of its float and showing low in the warning cluster.

Yes, it has.

It's a reed switch which plugs in at the bottom of the expansion tank.

https://www.fullfatrr.com/forum/post211489.html

Easy 1 minute job and you don't even need to remove the tank.

I would just replace the expansion tank, complete with new sensor. The "sight glass" inside the tank gets clouded up which means the sensor can't do its thing, just fitting a new sensor may not work. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Keep in mind that "coolant level low" doesn't always mean that the liquid isn't up to the mark. The sensor measures the concentration of the coolant as well and if it isn't between 40-60% concentration the sensor will read that the level is low. Try adding some undiluted coolant and see if that helps. Just make sure you are adding the exact same type of coolant as mixing different types can be bad. 2009 L322 SC

Many thanks guys I’ll try a clean then , and see what happens.

Must say I have added pure coolant , but wouldn’t know what was in before. I’ll clearfsjlt and test SG independently.

The sensor is fitted like a bayonet light globe.
Reach under the tank, twist the sensor housing a quarter turn, lower and remove. Unplug from cable.

The reed switch in the sensor is worked by a magnet on the tank float. Test the sensor with a multimeter on continuity setting by moving a (fridge) magnet towards and away from it.

The windscreen washer tank has an identical sensor, but it is a little harder to remove because of the plastic underskirt in front of the left wheel arch. A simple swap makes a temporary repair.

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