C2 Coolant Level Low error

[amallaburn]

Got a friend's Citroen C2 VTS 1.6 petrol 2009 I've been helping him with.

Mechanic recently replaced Steering rack since then he has been getting a Coolant Level Low error popping up on dash.

This fault does not show up in standard OBD reader (cheapy ELM327) using Torque Pro.

I have recently got Lexia, (V: 7.02) when I try to read the Fault Codes log section it crashes. So unsure if I can use this.

Not sure where the sensors are related to this fault. Can come on intermittingly, especially when turning steering wheel.

Coolant level is fine, above min, below max.

Car is not overheating (checked through Torque Pro)

Been told there is either a green or blue sensor, managed to get to the green sensor (2 way) right of the engine behind a metal plate, on female connector managed to get a resistance reading of 3.94kOhms 20 mins or so after engine was off. Couldn't get probes in to test the socket next to engine with the male pins.

VIN: VF7**************[VIN obfuscated, can be read by forum staff]
RPI: 20599

Recently been through an ABS / ESP / Can Bus problem which turned out to be water ingress in the brown 28 Way connector located on PSF1/BSM/Under bonnet fuse board, not sure if coolant related stuff is in this connector where few other of the pins are quite brittle (the fuse board is being replaced ASAP)

[ozvtr]

The C2 does not have an actual "coolant level sensor" that measures the level of the coolant. However there is a sensor (blue) under the thermostat housing that measures the temperature of the cylinder head (NOT the coolant temperature!!). When the cylinder head temp gets to about 115'c (if I remember correctly) the sensor goes open circuit. The theory is that the engine must be low on coolant if the cylinder head gets that hot.
Both this sensor and the (green) coolant temperature sensor are directly connected to the engine ECU, in fact they share a common line. On the MK1's if this sensor goes open circuit, all of the temp bars on the dash come on. I know that this is a MK2 and the dash only has an over temp light but the center display says "coolant level low" in this situation. Hope I made myself clear there?
From what I can interpret from the circuit diagram the coolant low sensor provides the earth for the coolant temp sensor. When the coolant low sensor goes open circuit there is no earth for the coolant temp sensor and it goes off the chart!
Given some of the other problems with this car, I would check the engine ECU electrical connectors for corrosion too.

Just an idea, check the earths from the negative of the battery terminal, to the gearbox and chassis.

[amallaburn]

Thank you Ozvtr, lifesaver on this forum

How do I get to the blue sensor?

And what do the engine ECU connections look like?

My knowledge of cars doesn't extend much beyond audio

[ozvtr]

The

Thank you Ozvtr, lifesaver on this forum

Only when it comes to C2's and C3's.

How do I get to the blue sensor?

And what do the engine ECU connections look like?

The blue sensor is under the thermostat housing, sort of below the green sensor. To inspect it you should remove the air filter box. There is only one wire to it. Normally it provides an earth to the green sensor. So you can check for continuity from the single pin to a metal part of the engine.

The engine ECU is in the battery box next to the battery. FYI the power steering ECU sits at the back of the battery box. The engine ECU has three big connectors on it. Remove the connectors and inspect for moisture/corrosion.