Mk3 Focus, faulty air temperature sensor, is it actually important?

[nitten_traveller]

I have a mark 3 Focus, 63 reg

My question is: how important is knowledge of the outside air temperature for the proper running of the car?  I've noticed that the value displayed on the dashboard usually bears no relevance to reality.  This morning, for example, it read -13 C which was clearly wrong (it was cold, bit of frost on the windscreen, but not that cold; Mrs nitten_traveller has a Ka also parked outside our house and it read 3 C).  Personally I don't need to know the temperature outside, but I am wondering if the car needs to know this in order to regulate things properly under the bonnet?  Or is it purely for driver convenience?

The nearside side mirror has damage which was discovered during service, by Ford, last week (see attached picture).  I've had the car since July but didn't spot the damage until it was pointed out after the service. I've bought but not yet installed a replacement lens cover for the side mirror bulb.  From reading on here and elsewhere I see that the little lump under the door mount is the air temperature sensor.  It's possible that, if the mirror was struck by something, that the sensor itself is damaged.  I am wondering if I need to investigate/replace the sensor or if I can just let the sleeping dog lie. 

All advice will be much appreciated

 

[TomsFocus]

The engine ECU uses temp sensors in the air intake and coolant to determine the correct fuelling amount, not the outside temp sensor.  However, if you have auto heated screens, they may be activated by the outside sensor.

[nitten_traveller]

Thanks very much.  The cabin heating system is not automatic so there's nothing to worry about there. 

The car's auto start/stop rarely works; I read that this will deactivate in cold weather so if the car was using the outside sensor to judge the temperature then obviously this would cause a problem (though I quite like that the auto start/stop doesn't seem to work!).

[Micro]

If you don't have climate control inside the car, then i'd personally change it (OCD!) but if you can live with it then no problems.

The work vehicles sensors sometimes go wonky, but being French it upsets the climate control. Outside temp reading 40+ degrees, every setting on the climate control except HI is the coldest AC.

[nitten_traveller]

On 12/1/2017 at 5:31 PM, Micro said:

If you don't have climate control inside the car, then i'd personally change it (OCD!) but if you can live with it then no problems.

It's fine with me.  Climate control is not really needed in Scotland.  Weather control, on the other hand, now you're talking!

We inherited, rather than chose, the car but as it's a good decade younger than my aging Laguna we decided to keep it.  It's great to drive - I love how nippy the 1L engine is - and it makes my Laguna feel like a plodding tank.  

[TomsFocus]

On ‎01‎/‎12‎/‎2017 at 2:05 PM, nitten_traveller said:

Thanks very much.  The cabin heating system is not automatic so there's nothing to worry about there. 

The car's auto start/stop rarely works; I read that this will deactivate in cold weather so if the car was using the outside sensor to judge the temperature then obviously this would cause a problem (though I quite like that the auto start/stop doesn't seem to work!).

I meant the heated front and rear screens, these can come on automatically below certain temps.  But I'm not sure if they're set like that from the factory on the Mk3 Focus or if it's only something that is only activated after sale.  Obviously if the car thinks it's cold enough to activate the screens it'll use a lot more electric/fuel with those on unnecessarily.  The stop start will also not activate with that sort of load on the alternator.  Now you mention it, the stop start may use the outside sensor as one of it's many data points.

 

[drsdriver]

I’ve found the stop start has no bearing on outside temp or engine temp . 

My stop start has always worked from day one , and every journey works faultlessly. 

The reason I say it has no bearing on outside temp and engine temp, is that my stop start works even at 1c and even after my car has been parked up all night and then driven literally to a roundabout 300 yds away, the stop start still works. 

Regarding the outside temperature sensor, I thought it was near the front radiator grill ! But I may be wrong. 

[nitten_traveller]

3 hours ago, TomsFocus said:

I meant the heated front and rear screens, these can come on automatically below certain temps.  But I'm not sure if they're set like that from the factory on the Mk3 Focus or if it's only something that is only activated after sale.  

 

Oh I see.  I have heated front and rear screens but the don't seem to switch on automatically.  Even at "-13 C" I had to switch them on myself to de-ice the glass.

1 hour ago, drsdriver said:

I’ve found the stop start has no bearing on outside temp or engine temp . 

 

I wonder if it is the battery in that case.  I don't think it's been changed at all and the car has not done a lot of miles (17K give or take) for its age.  Mrs nitten_traveller's KA also had non-working auto start/stop until the battery was replaced and it started to work again.  The part of me which thinks that everything should work properly wants to investigate the start/stop and the air temp sensor more closely; the frugal part of me says that there's little point in spending money on this.

Thank you all for your comments.

[JW1982]

On the Focus MK3/MK3.5 the outside temperature sensor is integrated into the passenger side wing mirror housing.

The damage to the mirror is most likely also the reason of the defective temperature sensor. 

[drsdriver]

2 hours ago, JW1982 said:

On the Focus MK3/MK3.5 the outside temperature sensor is integrated into the passenger side wing mirror housing.

The damage to the mirror is most likely also the reason of the defective temperature sensor. 

That’s good to know for future reference. 

Im on the battery either needs changing or try trickle charge over night if you have a charger.

If you can when driving, try to keep all the electrical accessories off so it gives the battery chance to charge up. 

[isa94]

Hi,

I have a similiar problem. But in my case the interior temperature sensor seems broken, because it shows 103 °C. Furthermore, my ford focus mk3 1.0 ecoboost is having P2188 code. The mechanic said that the faulty interior temparture creates the failure because interior temperature influences the ECU as well. My question is, why the manufacturer set interior temperature as a parameter for the engine? and what is the purpose?

Thank you for everyone who answer my question.

Best regards.  

[Rosie12]

I have a 2011 Ford Focus and want to change the air temp sensor in the wing mirror. Any ideas on how to get to it? Even when I strip the mirror down I still cant seem to get to the sensor which seems to be under the spring mechanism for the mirror to fold?

[MACH1000]

Just been told that the sensor is NOT replaceable - so a whole new mirror is needed. That sounds painfully expensive!

[JW1982]

The outside temperature is part of the mirror housing assembly and is not available as a spare part from Ford.

There are however alternatives:

A similar size/shape temperature sensor for example from Peugeot/Citroen (part number 6445F9) can be installed with some minor modifications. This temperature sensor is known to have the exact same electrical specifications as the original temperature sensor.

 

[Darko_croatia]

Hi

@JW1982 .. what do you mean by minor modifications?

@Rosie12   did you manage to get to the sensor?

[JW1982]

Minor modifications means that the sensor needs to be spliced into the original wiring and the sensor needs to be fixated into the mirror housing with adhesive.

[Phil3747]

4 hours ago, Darko_croatia said:

Hi

@JW1982 .. what do you mean by minor modifications?

@Rosie12   did you manage to get to the sensor?

Might be cheaper buying a second hand one from either a scrap yard or eBay ??

[Darko_croatia]

1 hour ago, Phil3747 said:

Might be cheaper buying a second hand one from either a scrap yard or Ebay ??

For sure...here in Croatia 250euros original new one

[Phil3747]

What is the problem with yours Darko ??

I had this issue with mine a few days ago but managed to fix it ...

 

[Darko_croatia]

1 hour ago, JW1982 said:

Minor modifications means that the sensor needs to be spliced into the original wiring and the sensor needs to be fixated into the mirror housing with adhesive.

This is really minor to to...and price is also nothing compared to mirror

https://www.cars-equipment.com/en/shop/sensors-2/6445f9-sensor-outside-outdoor-transit-air/

[Darko_croatia]

4 hours ago, Phil3747 said:

What is the problem with yours Darko ??

I had this issue with mine a few days ago but managed to fix it ...

 

I have noticed engine fan is working full speed. FIrst idea regeneration process, but than notice 43C on display and acutaly outside was maybe 4 C.

Turn car off, fan stopped it few secs. Starting again after 30 sec, showing temp 12C and until car is stopped it is same temp. I drove it again and temperature goes again up like counting seconds , 13,14,15----- to 46

Next day starting temp 6, outside 0 and again....after 100m of driving again on 40C

[Phil3747]

That sounds similar to my fault, although my temperature display went down rather than up. It could be worth just checking and cleaning the connector behind the tweeter cover as shown in the above Youtube clip as that worked for me ??

[ardacavdar]

We disassembled my friend's Focus Mk3's passenger side wing mirror to try to replace faulty ambient temperature sensor.
The process was great until we hit that big electric mirror spring and it seemed impossible to move forward.
There are 2 more screws which seems like the solution to a way to remove the sensor but it's almost impossible to fit a T8 screwdriver in there.

Everyone said disassembling the sensor is impossible but those screw are sitting there and simply can't reach them.

So, I just want to ask if you guys managed to find a way to remove the sensor from the body?

[Kitchenfitter]

Any success? 

Have a similar prob