The one in the engine block that indicates temperature on the dash board. It cost me around US$70 including labour. I realised what the problem possibly was when it went into limp mode and the temperature gauge on the dash was in the red zone. I lifted the bonnet (hood) and there was no steaming...
My limp mode problem turned out to be a faulty engine temperature sensor. The ECU got a false signal that the engine was over-heating. Turbo was then shut down.