Erratic temperature guage

Hi, my 2003 C3 auto is having a few niggles, but nothing that stops it working.
The temperature gauge usually shows 3 lights when up to running temperature, but just occasionally the temp gauge lights will all come on, give a few beeps then go back to 3 lights, all in the space of 10 seconds or so. The engine is definitely not overheating, I have checked it with an infrared thermometer and the temp is around 85 degrees when it does the trick with the gauge.
My local garage has had it in and drained and flushed the coolant, checked the thermostat and the fan, all working correctly. They have also changed the temperature sensor.
It still does the thing where the temperature gauge goes to maximum for a few seconds.
I have also had the emissions warning light come on, but not at the same time as the temp gauge problem, could this be connected ? My garage has plugged in their diagnostic tester and there was a fault logged, saying something along the lines of 'a sensor could not be trusted', not sure if the garage was using Lexia or not.
Any thoughts on this please ?

Hi kjharry

kjharry wrote:My garage has plugged in their diagnostic tester and there was a fault logged, saying something along the lines of 'a sensor could not be trusted',

kjharry wrote:Any thoughts on this please ?

Connect your own OBD reader (get one here) and find out what the code actually is, rather than 'something along the lines of' - which doesn't help very much.

With the actual code you can get a better idea of what is wrong.

If you wanted to get serious, try lexia (from here) but although its much more comprehensive and accurate, its many more hours of work to get running.

Right, found a really good guy in Swansea who sorted this (have a look in the club area for my recommendation for him).
Indepth diagnostics revealed it to be a fault in the bsi with a component on the main board, a resistor that is breaking down under load when the temperature in the engine bay rises (such as being stuck in traffic).
It seems that this fault wont affect the driveability of the car and that a permanent repair would mean changing the bsi which would exceed the value of the car. I will just have to put up with the occasional beep from the temperature warning system.
Hope this is of help to other people who have asked about the problem.

Thanks for the update. Yes, a kit of bsi ecu and key, the swap and subsequent programming makes this only economic if you DIY it.

Some of the BSI units do open up and you could possibly change the component but if a mistake is made, it's back to fitting a kit.