C4 thermometer

[Vic Evans]

The thermometer on my wife's 2014 C4 Millenium has gone mad showing anything from -2 to 6 deg this afternoon when it's actually about 12 deg.
I'm assuming the sensor is in the mirror.
Any ideas what's causing this?

[GiveMeABreak]

If the outside temperature sensor has failed it will be either the wiring to it from the door aperture from opening and closing the doors over time weakening the wiring or the sensor itself which means replacing it. It's shown as a small dimple on the underside of one of the exterior mirrors.

New sensors come with a couple of strands of wiring and are quite cheap, that need to be spliced into the original wiring, so be very careful not to cut the wiring too short of the old sensor id replacing it.

Whilst the sensor is playing up, be aware it will affect your climate control system and Air Conditioning functionality

[Vic Evans]

Cheers Marc, that was a quick response.
If it going to affect the climate control I'll get her to take it to our local Citroen garage where the owner is very helpfull.

[GiveMeABreak]

It generally involves some dismantling of the wing mirror, and removal of the door card to get to the wiring to snip the old one and splice in the new.

[Vic Evans]

My wife was out & about with the car quite a lot today & apparently the thermometer was reading what she expected.
Last evening I was checking out the cable route via the door flexible & wiggled it. Dodgy cable maybe but not really likely as it's a LHD & it's usually driven solo so the RH passenger door where the sensor mirror is gets little use.
Mind you I've just remembered that this mirror got hit a year or so ago when she was in the UK & the damaged shell was changed by a body shop owner pal of ours although the thermometer has read OK until yesterday.

[xantia_v6]

Those sensors are fairly unreliable but cheap, so replacement is probably a good substitute for spending a lot of time on diagnosis.

[Kees]

Hmmm, people here speak the sensor is cheap.
A few months ago mine say +35 degree when it was outside minus 1, so the airco blew cold air inside.
I went to dealer just to buy a new one for a new one .
The man say, no problem i have it in stock.
I ask the cost, he say.......68 Euro!!!
So i ordered the part Ali Express and get 2 of them for the price of 9 Euro.
P.s. i liv in the Netherlands.

Greetings,
Kees.

[Vic Evans]

Thermometer still reading correctly with no garage intervention except a wiggle of door loom flexible by your truly.
I'll ask our Citroen garage owner what he thinks about this the next time I'm passing but not sure what he can do if there's no faults at present.

[CitROeNALD]

Is it a diesel?

If so, from what I understand, that sensor might not just be for driver information. It seems to be integral to the proper functioning of the engine.

I mention this after watching a lot of the O'Riley's videos on DPF issues on youtube. Very often flummoxed garages overlook this small and cheap sensor as a cause of the DPF getting blocked due to incorrect values being sent to the ECU and therefore (I assume) impacting fuel/air mix ratios or something.

Quite often this is only spotted after multiple more expensive attempts to repair the issue caused by this sensor.

So, it seems a non-functioning or inaccurate air temp sensor on the door could cause you issues further down the line, so it is important you get it working correctly. I have no idea if this could impact a petrol engine in the same way.

Just thought I'd add this.

[Vic Evans]

Thanks for that info. It's a 1.6 Hdi
I've driven it a few times since the initial problem & every readout such as fuel consumption/ Km remaining etc seem normal on like for like trips into town.

[CitROeNALD]

Thanks for that info. It's a 1.6 Hdi
I've driven it a few times since the initial problem & every readout such as fuel consumption/ Km remaining etc seem normal on like for like trips into town.

Yeh, I'm not sure it would present any further clues to it affecting engine management, on standard readouts anyway, which is why people seem to totally miss it as a factor in contributing towards DPF issues.

All I've gleaned from the videos I've watched is that the engine management somehow relies on that sensor, and somehow, without correcting the fault it can be a big contributor to the DPF blocking up or having ongoing issues.

[Vic Evans]

Just a thought.
Would any problems with thermometer show on vehicle fault log as there's nothing on it from day one of this 'problem' ?

[CitROeNALD]

This is one of the videos I am referring to.

From the looks of his diagnostic tool, nothing obvious even comes up there relating to the failure of the temperature sensor. Which seems to be a big reason it's importance is missed.

But, you'd have to get the right tool and be able to check the logs to see if anything comes up.

Watching that video again, the sensor may play no part in engine management (fuel/air mix etc), but....it may simply be a trigger switch to allow/disallow a process. If it is non-functional or giving bad values, that process cannot occur.