Hymer544PL
New member
This thread is to record how I fitted a replacement temperature sensor on our Hymer B544 PL motorhome that is based on a Fiat Ducato X290.
Symptoms: Temperaure shown on the display was extremely high and erratic, often over 80°C, finally settled at ---°C so it looked like the sensor had failed.
A great deal of searching the internet showed that many people had the same problem, and it was caused by failure of the external temperature sensor. Normally this sensor is fitted to the bottom of the mirror on the driver-side, that is OK on a standard van or van conversion motorhome. Many motorhomes (A class) have custom mirrors and bodywork, so the external temperature sensor is placed somewhere else by the builders of the motorhome, and there is the problem, WHERE is the sensor? Eventually I decided that fitting a new sensor was the only sensible option.
Thanks to HughJampton on this forum for the X290 Converter's Manual that enabled me to solve this problem.
Steps in solving the problem
The sensor was attached to a new support bracket as shown below . . .
then attached to one of the rear support brackets of the vehicle using cable ties, as shown below . . .
The sensor should remain dry there.
the wire from the new sensor is routed through and existing hole into the battery box of the vehicle, then to the appropriate connector.
In total this project has probably taken 3 days, if I had known what I now know I would have finished it in 1/2 a day, but that's how things go.
Hope this helps other people with the same problem.
Final result, temperature showing . . .
Symptoms: Temperaure shown on the display was extremely high and erratic, often over 80°C, finally settled at ---°C so it looked like the sensor had failed.
A great deal of searching the internet showed that many people had the same problem, and it was caused by failure of the external temperature sensor. Normally this sensor is fitted to the bottom of the mirror on the driver-side, that is OK on a standard van or van conversion motorhome. Many motorhomes (A class) have custom mirrors and bodywork, so the external temperature sensor is placed somewhere else by the builders of the motorhome, and there is the problem, WHERE is the sensor? Eventually I decided that fitting a new sensor was the only sensible option.
Thanks to HughJampton on this forum for the X290 Converter's Manual that enabled me to solve this problem.
Steps in solving the problem
- Carefully studied the Fiat Ducato Converter’s Manual that shows the electrical connections. Established that connector Y001LA was what I needed.
- 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. 10k resistance is 25°C on the display.
- 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.
- Finding the Y001LA connector on the motorhome, it is behind a lot of plastic fascia and there are NO labels or identification marks on any of the connectors. I had to remove each connector and count the pins carefully.
- On the socket side of the connector the wires are coded using Fiat wire colours but on the plug side the wires use Hymer wire colours so they are totally different. I did not recognise that for some time.
- Some of the pins in the connectors are not used, so there is no wire, but you still need to count those pin positions, otherwise you cut the wrong wires, that's what I did and then spent a long time wondering why I saw no change on the temperature display. To ensure that I finally had the correct wires I attached a variable resistor in place of the sensor so that I could simulate the temperature change.
- Finding a suitable place to locate the new sensor so that it would not be affected by heat from the engine and also finding a place where the new wires could be routed conveniently.
The sensor was attached to a new support bracket as shown below . . .
then attached to one of the rear support brackets of the vehicle using cable ties, as shown below . . .
The sensor should remain dry there.
the wire from the new sensor is routed through and existing hole into the battery box of the vehicle, then to the appropriate connector.
In total this project has probably taken 3 days, if I had known what I now know I would have finished it in 1/2 a day, but that's how things go.
Hope this helps other people with the same problem.
Final result, temperature showing . . .