Fiat X290 external temp readout

[grahamw]

My X290 had its instrument panel replaced last year because of spurious dimly lit warning lights. Problem solved. However, I noticed that the external temperature readout was giving odd results. Usually in error by about 10 degrees C. I reported this to the garage who apologised for not "fully resetting the system" and I was assured that everything would now be ok. I'm now driving around in good sunny weather with the ice warning symbol illuminated and a temperature readout between 2 and 3 degrees C. The warmer it is outside the greater the discrepacy appears to be.

 

To have the knowledge is to have the power and I'm afraid at this stage my knowledge of the system is limited. I believe the sensor is located in one of the external mirrors but as for "resetting of the system" or a means of recalibrating the system I have no knowledge. Or is it simply a malfunctioning sensor which needs replacing? It represents an obvious malfunction on the dash and at MOT time one wonders how this would be viewed not to mention that I effectively lose an important warning because of the systems unreliability.

 

Can anyone throw any light on what might be the cause and hence what needs to be done?

[spospe]

I had this problem on an X250 and it was eventually resolved by changing the driver's door mirror. The temperature sensor is located at the bottom of the mirror case and necessitates the cutting of a hole if fitting mirror protectors. It seems over-the-top, but seemingly you cannot get just a replacement sensor, the whole mirror must be changed.

[Keithl]

Graham,

 

The answer is simple! The wires to the sensor are reversed.

 

The sensor will be a thermocouple which is a 'junction' of dissimilar metals which produces a very small voltage proportional to the temperature (as low as 0 to 2 mV) . This voltage is then measured relative to a known junction.

 

The difference in voltage between the thermocouple and the reference junction is directly proportional to the temperature. If the wiring to the thermocouple where to be reversed then the difference would be subtracted from the reference not added and hence would go down as the temperature was actually rising.

 

Quite how you explain that to the dealer is beyond me but that is why you are experiencing the problem.

 

PS I am regularly involved in instrumentation on cars at work so have experienced this problem many times before. The problem is finding where the connections are reversed or you can get more strange readings!

 

Keith.

[Robinhood]

I had similar issues with my X290 not long after purchase. Wrong readings (in both directions) and ice warnings at over 20 degrees (real temperature).

 

The temp sensor is (as already posted) in the drivers door mirror, and not being separately available, the whole mirror needs replacement.

 

Thankfully, mine was still in warranty.

[Derek Uzzell]

The procedure involved in removing a Fiat Ducato X250/X290’s instrument-cluster is described here:

 

http://www.lockwoodinternational.co.uk/media/wysiwyg/instructions/Fiat/C120_C124_Etc_Fiat_Ducato.pdf

 

Four screws are removed, the instrument-cluster is lifted out of its dashboard housing and a single ‘locking’ multi-pin electrical plug/socket is disconnected (FIG 5 photo on link). Replacement is equally simple.

 

It’s a leisurely 10-minute ‘garage forecourt’ task that does not require battery-disconnection and I’ve done it several times on my Rapido. Disconnecting the cluster’s plug/socket will cause transitory readouts (eg. date/time) to be lost and these will need to be reset. But merely removing/replacing the cluster requires no computer-system intervention, so I’m unsure what Graham’s garage’s comment about not "fully resetting the system” refers to.

 

When my 2015 Rapido X290 was serviced a few months back, software revisions were applied to it that cause the instrument-cluster to illuminate whenever the vehicle’s ignition is switched on. This revision was originally provided only on demand to help improve speedometer readability, but (as I did not ask for it to be done) it’s apparently now a ‘freebie’ within a Fiat Professional service. A software revision performed at the same time as Graham’s instrument-cluster swap MIGHT possibly impact on the external temperature readout, though (as spospe and Robinhood have said) it’s much more likely that the fault lies with the sensor in the mirror.

 

As far as I’m aware there is no means to ‘correct' the external temperature feature’s readout. The UK’s MOT-test demands that specific ’tell tale’ lights/information must be provided on a vehicle’s instrument panel and that, when provided, must function properly. But a readout giving the external temperature, or warning of icy weather conditions, is not mandatory, so the malfunction on Graham’s vehicle should have no impact at MOT time.

 

I think Graham’s motorhome (a bespoke PVC based on a self-bought van) will be out of warranty now, but as the appearance of the extenal temperature readout fault was apparently coincidental with the instrument-cluster replacement and the garage seems prepared to accept some responsibility for the fault, it would be worth trying to get the garage to fix it, which - as advised above - will probably mean a new mirror.

[Keithl]

I would imagine Fiat has implemented a modification or 'improvement' at some point after Graham's van was built which involved changes to either the instrument panel, wiring harness or mirror sensor and that new parts are not compatible with old vans.

 

Now graham has had a new instrument panel fitted it is not compatible and hence throws up this 'error'. Quite how to fix it may need referring to Fiat technical.

 

Possibly the first thing to check is that the new instrument panel was actually the correct part against the VIN of his van,

 

Keith.

[Robinhood]

You may be correct, Keith, but I fear you may be overlooking the obvious.

 

My fault was not associated with other work. Faulty temperature readings are a relatively commonly reported Ducato problem.

 

I'd go with it being a faulty sensor.

 

I found the ice warning annoying, and would have replaced it myself if we'll out of warranty.(If I were Graham, I'd try to blag the dealer.)

 

Mirrors can be sourced much cheaper than Fiat parts, but be careful to get one with all the options you currently have.

 

'wingmirrorman' is probably a decent source.

 

 

[grahamw]

Many thanks for the very useful comments. As has been correctly pointed out the vehicle is now out of warranty but I will refer the problem back to the garage as the issue was brought to their attention during the warranty period. We'll see what they have to say!