Following on from my previous post about the Hymer outside temperature showing —°C, after extensive research on the internet and various forums the problem has been fixed.

The problem was the external temperature sensor, the sensor had failed, that problem was not really difficult to diagnose. The bigger problem was finding the location of the original external temperature sensor on the Hymer (Fiat Ducato). In fact the sensor has still not been located.

The base chassis is a Fiat Ducato, (X290 is the Fiat designation for the base vehicle). This is used by Hymer is Germany to built the finished motorhome. As far as the electrics of the vehicle go, Fiat provides a series of large connectors that link into the Fiat Ducato electrical system. Hymer then add their layer of electrics on top, using the Fiat connectors. This starts to get complicated because Fiat use one set of wire colours and Hymer use a different set of wire colours.

After an extensive search of the vehicle, under the bonnet, under the vehicle, inside the driver’s door and the mirrors the original external temperature sensor could not be found. More searching on the forums found a post where the vehicle owner had been unable to located the original temperature sensor and so decided to cut off the appropriate wires and install a completely new external temperature sensor and connect it to the original wires. That is what I did. The most difficult part was determining which wires needed to be used.

• Carefully studied the Fiat Ducato Converter’s Manual that shows the electrical connections.
• Found the appropriate connector on our Hymer and established the correct wires that go to the external temperature sensor.
• Cut the wires and attached a variable resistor set to 10k ohms, this is to confirm that these are the correct wires.
• Purchased a replacement thermistor temperature sensor.
• Constructed a new external temperature sensor housing and found a suitable location on the Hymer.
• Attached the new sensor and installed wires to connect it.
• Tested and confirmed it works.

Not a quick and easy fix but very satisfying in the end. The original sensor is still somewhere on the vehicle but can’t be found.

I have put together a page of photos and more information about this project, here.