Outside Temperature Sensors.
 

Putting this here because i guess it's a technical thing?

When an outside temperature sensor fails it will affect the overall running of the car.?

Am i correct in saying this?.

On my Ford Ka 1.2 (2014) The outside temperature sensor failed and the car was running rough, especially when cold.

Since replacing the sensor the car runs way more smoothly.

Here's a snip i copied and pasted from the net.

"A faulty ambient air temperature sensor can have a significant impact on a vehicle's performance, fuel economy, and safety. The sensor's role in providing accurate temperature readings to the engine control unit is critical to optimizing the air-fuel mixture. However, if the sensor malfunctions and provides inaccurate data, this can lead to engine misfiring, rough idling and even stalling. These problems can cause the engine to run erratically and disrupt the smooth operation. In addition, inaccurate readings can lead to an unbalanced fuel/air ratio, resulting in inefficient combustion and reduced fuel economy. Many car owners are unsure about how to test their ambient air temperature sensors. The easiest, and most convenient way is to invest in a multimeter."

What i would like to know is there any truth in this...Concrete evidence that the Outside Temp Sensor is hooked up to the ECU and how much fuel the engine gets?

I'm clutching at straws here. I guess Ford would know but they ain't going to tell me willingly.

What do you know?

Thanks guys.

All vaguely modern cars have an inlet air temperature sensor (IAT). If that is defective then yes - running can be significantly affected. The description you quote is exactly right if they are describing a faulty IAT. I've not heard of this sensor being called the "ambient air temperature" sensor - to my knowledge it's always IAT.

We need to check the wiring diagram to see if there is a separate ambient air temperature sensor. If not, then presumably the IAT is used for both purposes. It makes sense; after all the inlet air is pretty much at ambient temperature. If it is used for both purposes then presumably it could be called either term, and that would add weight to Ford's statement.

So here's the obvious question: is the external temperature reading on your dashboard obviously wrong?

Great reply thank you.

I fitted a brand new outside temperature sensor and it works perfectly.

Previously there was no reading at all on the dashboard. Just a set of dashes like this ---

I will try and get hold of the wiring diagram, as you say, that should show how it's all connected up.

That's interesting. Where abouts is it fitted?

Is your car running badly even with the new external temperature sensor fitted?

Ah, so on your car there is a TMAP sensor fitted in the inlet manifold. Temperature and manifold absolute pressure.

That will be the one the engine management unit uses, obviously, and if it's bad the engine will run badly. Can you confirm that the external temperature sensor you changed is a different device?

The external temperature sensor is mounted just behind the front bumper near the lower grille and is a different sensor to the one mounted in the inlet manifold.

Perfect, thank you!

@OddSox: regardless of the terminology used, the symptoms described in the Ford statement align with a faulty inlet air temperature sensor, which in the case of our Rovers is integrated into the TMAP (temperature and manifold absolute pressure) sensor on the inlet manifold.

I know of no mechanism by which the external temperature sensor can affect the running of the engine in our Rovers.

I don't have enough knowledge regarding the Ford Ka; perhaps it uses the same sensor for both functions, or perhaps Ford use different terminology.

The outside temperature sensor on the ford ka is located in the near side wing mirror.

Since fitting a new one it did seem that the engine was running smoother especially when cold.

I saw an AA man parked up yesterday so i stopped and asked him about the outside temperature sensor and he said that it doesn't affect the running of the engine to his knowledge.

The more i think about it the more i think that it doesn't have anything to do with the running of the engine.

There are other sensors that deal with that so why would it?

I think it's just coincidence.

All it is, is the engine seems to idle very slightly rough when warm.

The air filter is brand new and i've had all 4 spark plugs out and they were all light grey and very clean and the car does 43+mpg, so that covers the main operation of the engine.

It's only a little 1.2 and the engine is a single cam Fiat unit and it's covered 92K.

It might just be me, being used to a very smooth running car then getting in the KA and expecting it to be just as smooth when in reality it's never going to be.

I will have a look at the TMAP sensor but i would have thought if there was anything wrong with that it would throw a fault up on the dashboard?

Great to learn about these things though and as always great advice.

Thank you.

Have you considered using an on-board diagnostic (OBD) tool to check whether a temperature sensor error has been logged?

That's a good shout, i hadn't thought of that.

If there was a fault recorded it will need to be cleared wont it.

I don't have an OBD scanner but my local mechanic does.

I'll get it checked ASAP and report back.

Cheers.