Additive Low Level Sensor Fault

[Suffolkpete]

I've had the minimum level fault come up on my 2002 C5 2.2HDi. I've topped up the tank (DPX42) and reset the ECU, I've got a Lexia, but still the fault persists as a permanent fault (P1435). Is the sensor faulty or is it the ECU? The parts list on Citroen Service doesn't show a sensor, although I suspect that is is described there as a harness, like the fuel cap sensor. What do the experts think?

[Lighty]

The sensor is built into the Eolys tank, and can't be removed, sometimes they will reset after a week or so with fluid in.
Otherwise it's a new tank,methinks they are about £200

[Suffolkpete]

I've checked the continuity of the connections between the ECU and the additive tank and all are ok, but when I try to measure the resistance between pins 1 & 2 (level sensor connections) on the additive tank, it shows an open circuit which leads me to suspect that the sensor is faulty. £200 just to remove an error message is a bit excessive so my question is: given that the sensor is a thermistor, can I replace it with a resistor to fool the ECU into thinking that the level is ok? If so what value? I can't see anything wrong with this, I believe that later cars don't have a sensor anyway and I will still get an alarm when the "Ash in filter" limit is reached.

[CitroJim]

How does a thermistor measure a fluid level? Is there a marked temperature difference between it being submerged in the Eolys fluid and in the open air?

[Suffolkpete]

Yes, I believe that's the theory, I have a similar arrangement for the oil level sensor on my Matra.