Hi all,

I've read a several posts and they all talk about cold starts.

First I had a leak in the radiator so that was replaced. Then the warning came on again when driving on the motorway but the coolant level was fine. The temperature needle floats around 80 then drops to the bottom.

The EML came on the other day and I had the engine coolant temp sensor (G62) implausible signal warning. So I replaced that today. 15 minutes into a motorway drive at 70, coolant warning light again. Coolant level is fine, I have hot air blowing out the vents, the fans don't come on as if it thinks its hot, you can feel coolant circulating through the system so there doesn't seem to be a blockage. I can drive around under 50 mph for hours and the warning light won't come on.

I know there is a second sensor near the radiator, but I didn't get a code for that one and I can't get a code now as the EML doesn't come on.

What can the issue be?

 

Yes, there are 2 Engine Coolant Temp sensors. One easy to get to on the rear(driver side) of the engine block that reports to the ECU for engine temp reporting and engine management. The other one is very hard to get to near the water pump that reports to the temp gauge in the dash.
I have issues with the one feeding the gauge in the dash. I can connect a code reader and verify believable temperature readings from the primary ECT sensor at the end of the engine block but the 2nd sensor is not reporting and causes a Check Engine Lamp. Mine is not a sensor issue and likely a wiring/continuity issue as the sensor was replaced and the at first intermittent then and almost constant CEL remains.
Years ago the CEL being on all the time would have driven me crazy. I'm now older, have a lot less money these days, the car was long past any warranty remedy, so I got over it and just plug my code reader in every now and then to make sure that is the only fault being reported.