Coolant Level Warning, Levels Fine - Faulty Sensor?

[J3FVW]

I was driving to work this morning and after about ten minutes (with the engine at normal operating temperature) the coolant warning level alert appeared on the dash. About five minutes after the initial beep and warning I stopped at a shop and when I restarted the car the warning beep and graphic on the dash showed again.

As I was slightly worried I called at my usual petrol station to fill up and asked the mechanic to help me take the bonnet off so that I could top the coolant level up. Strangely the coolant level was fine and as the mechanic verified was on the maximum level. This was what I would expect as only a month ago my mate changed the coolant temperature sensor which caused a loss of water so he topped the system back up again with the correct VW/Audi pink coolant.

After screwing the cap back onto the expansion tank and refitting the bonnet I restarted the car and no warning graphic or beep. Very odd.

The petrol station mechanic thinks the sensor in the expansion tank is faulty. Does this sound correct. If so is changing the sensor a relatively simple and cheap job or do I need to buy a complete expansion tank? Any help would be welcome as I like everything to be right on my cars and the A2 is running like a dream other than this hiccup.

Finally I must say a big thanks to Stringers petrol station in Pontefract and their mechanic for their help this morning - top people in a traditional family business

 

[Dave M]

I know its not much help Jeff but I would recommend a diagnostic scan which may or may not show a faulty sensor. Our A2,s are quirky little cars which occasionally have a habit of showing up faults which are quickly rectified by turning the ignition off and on again. Mine showed a steering sensor fault last month on start up but its never come up again. I have a simple diagnostic device which we could try when your free but I would recommend a more sophisticated set up - better detections.

Ta
Dave

 

[J3FVW]

I know its not much help Jeff but I would recommend a diagnostic scan which may or may not show a faulty sensor. Our A2,s are quirky little cars which occasionally have a habit of showing up faults which are quickly rectified by turning the ignition off and on again. Mine showed a steering sensor fault last month on start up but its never come up again.

Ta
Dave

Hope that's the case Dave. My trusty mechanic mate Peter seems to think at worst it will be a bad contact or some moisture in the electrics causing it. I'm relieved that everything is as it should be with the levels I just can't cope with warning lights and beeps - hopefully it won't happen again. You know me and my OCD

 

[TDIaholic]

Mine does this too if I start the car cold in the morning. The sensors is basically a switch with 2 prongs. The coolant shorts the 2 prongs, creating a circuit and this turns the dash warning light off. This means the sensor is also very unlikely to break, per say, but if the prongs get coated in slime / dirt from the coolant this can cause issues. The only way is to double check the connector and maybe spray the contacts inside with some electrical cleaner, and try to clean the contacts on the sensor itself. I haven't gotten around to doing mine yet as I will need to drain the expansion tank. I'll do it soon when I'm changing the temperature sensor and thermostat.

 

[J3FVW]

Mine does this too if I start the car cold in the morning. The sensors is basically a switch with 2 prongs. The coolant shorts the 2 prongs, creating a circuit and this turns the dash warning light off. This means the sensor is also very unlikely to break, per say, but if the prongs get coated in slime / dirt from the coolant this can cause issues. The only way is to double check the connector and maybe spray the contacts inside with some electrical cleaner, and try to clean the contacts on the sensor itself. I haven't gotten around to doing mine yet as I will need to drain the expansion tank. I'll do it soon when I'm changing the temperature sensor and thermostat.

Thanks for the superb explanation - I'll get my man onto it as soon as he can!