Citroen C4 Picasso - ambient temperature gone crazy.

osarusan

Hi all,

in my 2011 Citroen C4 Picasso, I was driving home when the ambient temperature displayed on the screen went from whatever it is today, say 14 degrees, up to 20, then 30, 40, 50, within a matter of a minute.

The light to indicate that the engine itself is overheating did not come on. When I got home I popped the bonnet and the radiator was warm - hot, but the coolant opened up without any pressure/spray, and the coolant itself seems to be at a full level.

Does anybody know where the ambient temperature sensor is located, and why it would suddenly race up like that? Is there likely to be a connection to an overheating engine?

Thanks.

Waterson

The ambient temp is usually measured by a sensor mounted behind the front grille of the bumper. There could be a poor connection on the sensor causing the erratic signal.

osarusan

Waterson wrote: »

The ambient temp is usually measured by a sensor mounted behind the front grille of the bumper. There could be a poor connection on the sensor causing the erratic signal.

Thanks, doesn't sound like there is any connection to an engine overheating at least.

CoBo55

Sensor probably fell out of its holder and is measuring under bonnet temperature.

osarusan

Actually, just went and checked, and the sensor is embedded in the underside of the driver's side wing mirror. Or, at least, the housing is there, perhaps the sensor got dislodged and travelled down into the bonnet.

Row

osarusan wrote: »

Actually, just went and checked, and the sensor is embedded in the underside of the driver's side wing mirror. Or, at least, the housing is there, perhaps the sensor got dislodged and travelled down into the bonnet.

Those sensors do give trouble...looks like this.. https://www.ebay.co.uk/itm/6445F9-External-Temperature-Sensor-for-Peugeot-206-207-307-407-SD/173936140164?hash=item287f66df84:g:6YEAAOSwGoRcijZm

osarusan

Car was untouched from 6pm yesterday to 2pm today, in the rain for a lot of the night, and when I started it, the temp immediately said 33 degrees and went up to 58 within a minute or so - so it is not an accurate reading at all (even for inside the bonnet somewhere), just a malfunction somewhere.

Are the consequences of this malfunction limited to me not knowing the temperature outside? Or an accurate reading necessary for anything important?

If it's the former, I won't bother to get it fixed until the next service, but if it is important in some way, I'd like to get it sorted earlier.

CoBo55

osarusan wrote: »

Car was untouched from 6pm yesterday to 2pm today, in the rain for a lot of the night, and when I started it, the temp immediately said 33 degrees and went up to 58 within a minute or so - so it is not an accurate reading at all (even for inside the bonnet somewhere), just a malfunction somewhere.

Are the consequences of this malfunction limited to me not knowing the temperature outside? Or an accurate reading necessary for anything important?

If it's the former, I won't bother to get it fixed until the next service, but if it is important in some way, I'd like to get it sorted earlier.

Don't worry about it, count yourself lucky it's only that sensor on one of them.

osarusan

CoBo55 wrote: »

Don't worry about it, count yourself lucky it's only that sensor on one of them.

Not sure what you mean...why should I count myself lucky?

kirving

The ambient air temperature sensor, in the mirror, is for a number of things:

A)To show you how hot it is outside
B)To pass information to the climate control system so that it operates as efficiently as possible.

( C) Certain cars may use the ambient temperature sensor as an additional aid to further improve engine efficiency in very specific circumstances, but this is really not of concern at all. )

The sensor must detect small changes in air temperature quickly. A big robust sensor would take longer to heat up or cool down in the air, meaning it would react too slowly, so the actual sensitive part of the sensor tends to be very small and delicate.

If you drove into a cool underground car park on a hot day for example, the car has to react to that very quickly, and not necessarily wait for the cabin temperature to drop, before turning off the air conditioning. There are other sensors too of course in the AC system, but they all work together to be as efficient as possible. Your AC should still work, but the Auto mode of you have it, might act strangely.

It's very common for them to break, particularly since they're in the mirror which can get hit or the internals get wet.

They can work in a number of ways, but a damaged sensor will give a strange reading as opposed to no reading - like you are seeing here. Is almost certainly did not fall into the engine bay and become hot.

If the temperature is stuck high, or low, that would indicate that the sensor is completely disconnected or completely broken.

It's likely to be a very simple fix, consisting of replacing the sensor. No need to worry about it causing any issues for the engine.

CoBo55

osarusan wrote: »

Not sure what you mean...why should I count myself lucky?

It's still running without the dash being lit up like a christmas tree:pac:
It hasn't eaten its way through 3 egr valves, 2 dpf filters, clutch and flywheel, at least one oil soaked turbo that has destroyed everything around it including your driveway... They were not Citroen's best effort.

CoBo55

Kevin Irving wrote: »

The ambient air temperature sensor, in the mirror, is for a number of things:

A)To show you how hot it is outside
B)To pass information to the climate control system so that it operates as efficiently as possible.

( C) Certain cars may use the ambient temperature sensor as an additional aid to further improve engine efficiency in very specific circumstances, but this is really not of concern at all. )

The sensor must detect small changes in air temperature quickly. A big robust sensor would take longer to heat up or cool down in the air, meaning it would react too slowly, so the actual sensitive part of the sensor tends to be very small and delicate.

If you drove into a cool underground car park on a hot day for example, the car has to react to that very quickly, and not necessarily wait for the cabin temperature to drop, before turning off the air conditioning. There are other sensors too of course in the AC system, but they all work together to be as efficient as possible. Your AC should still work, but the Auto mode of you have it, might act strangely.

It's very common for them to break, particularly since they're in the mirror which can get hit or the internals get wet.

They can work in a number of ways, but a damaged sensor will give a strange reading as opposed to no reading - like you are seeing here. Is almost certainly did not fall into the engine bay and become hot.

If the temperature is stuck high, or low, that would indicate that the sensor is completely disconnected or completely broken.

It's likely to be a very simple fix, consisting of replacing the sensor. No need to worry about it causing any issues for the engine.

Part A is correct.
Disregard sections B and C (complete rubbish)

Stoolbend

CoBo55 wrote: »

Part A is correct.
Disregard sections B and C (complete rubbish)

Depending on the car its not rubbish. Some of them rely on the outside temp for air conditioning to work.

wotswattage

Exactly the same problem for me last year! I had a mirror mounted temp sensor give intermittent trouble on a 2006 Volvo S40. It was mostly under reading temperature so the car thought it was -12°C (though it did give a high reading the odd time). Like a poster said above this can cause the climate control to act strangely but I didn't notice any difference in engine performance. The sensor itself on Volvos was a sealed unit set in resin -shouldn't just fail- so it's most likely wiring.

I traced the problem to the connector on the wiring harness going from the door to the chassis. The pins had become slightly corroded and luckily I was able to disconnect the connector and clean them.
Hopefully it's simple for you too OP!

kirving

CoBo55 wrote: »

Part A is correct.
Disregard sections B and C (complete rubbish)

Please explain to me how it's complete rubbish?