Boxer Temp Gauge Issue, Help Needed Please.

[kablpe]

Hi all. Help needed please. Boxer 2017 2.0ltr. Having an issue with temp sensor shooting up to full scale, only for about a second which then stops the engine, happens mostly when cold but also when hot, sometimes comes up with a message stop safely. Took to main dealer for diagnostic check, told pipe come off throttle doser unit, quoted £250 to replace, told when this replaced the temp sensor issue will also be resolved. Replaced pipe myself still same issue. Have replaced complete thermostat housing including sensor still the same. Next step I was going to replace earth lead from engine to chassis as it doesn't look to good. Any suggestions would be greatly appreciated as the van is getting slowly undriveable, I am halfway through conversion to camper.