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-50 Degrees


Simon Davis
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Following a jump start for a flat battery, (son left lights on), the outside air temperature is now shown as -50 degrees. It varies as the actual air temperature changes, so is working to a degree. (Sorry about the pun).

Is this likely to be a temporary fault or will the sensor be fried? If so, where is it?

Any advice welcome.

The car is a 2008 1.8 TDi Zetec Estate.

Simon

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Thanks for the suggestion. Unfortunately, it didn't solve it.

I forgot to mention that the low temperature "snowflake" symbol is also displayed, as would be expected if the temperature shown were correct.

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I would disconnect the battery for 30 mins and then try again. It solves a lot of little niggles! As said above though it will probably sort itself over a bit of time but it is annoying when things are not right!

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Following a jump start for a flat battery, (son left lights on), the outside air temperature is now shown as -50 degrees. It varies as the actual air temperature changes, so is working to a degree. (Sorry about the pun).

Is this likely to be a temporary fault or will the sensor be fried? If so, where is it?

Any advice welcome.

The car is a 2008 1.8 TDi Zetec Estate.

Simon

Where was the negative lead from the donor battery connected to on the other car ?

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Where was the negative lead from the donor battery connected to on the other car ?

I know what youre going to say Mark, ive always done it battery to battery over the years. Just for clarity what damage can it do like that on modern cars as opposed to on an earth point? Does it cause too much of an electrical spike or something?
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Its nothing to worry about, seen it a few times after battery disconnected, just leave battery connected, and use the car as normal, it will come down to the corect temperature eventually. .

Well done Ian, its good to have proper mechanics (or is that technician's?) on here to give expert advice rather than our guess work.

To be honest I didnt actually know the reasoning behind not jumping battery to battery, good old Google provided this -

The reason that it is better to make the connection to a bare metal part of the car rather than directly to the battery is to minimise the risk from sparks around the battery itself which in extreme situations could lead to an explosion (due to the ignition of hydrogen released from the battery when it is charging). Although exploding batteries might be very rare the consequences are horrific (as they are filled with acid) if you do connect directly to the negative pole of the dead battery you should wear eye protection - just in case you are the 'one in a million'.

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I know what youre going to say Mark, ive always done it battery to battery over the years. Just for clarity what damage can it do like that on modern cars as opposed to on an earth point? Does it cause too much of an electrical spike or something?

In short Wez yes it can.

Every handbook I've ever read, the A.A. & R.A.C. et al recommend connecting the negative lead to the body earth & the primary reason is to minimise ignition & consequent explosion & secondly this method minimises power losses through the dead car's earthing circuit so will ensure a better chance of a successful jump start.

There is also a body of thought that incorrect connection is responsible for '' frying '' some delicate circuits & that opinion is somewhat borne out on Forums where people say after jump starting my xxx no longer works etc

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Well done Ian, its good to have proper mechanics (or is that technician's?) on here to give expert advice rather than our guess work.

To be honest I didnt actually know the reasoning behind not jumping battery to battery, good old Google provided this -

The reason that it is better to make the connection to a bare metal part of the car rather than directly to the battery is to minimise the risk from sparks around the battery itself which in extreme situations could lead to an explosion (due to the ignition of hydrogen released from the battery when it is charging). Although exploding batteries might be very rare the consequences are horrific (as they are filled with acid) if you do connect directly to the negative pole of the dead battery you should wear eye protection - just in case you are the 'one in a million'.

Your google search beat me to it Wez - same answer though :)

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Update - after a rest, the system is now working properly, i.e. we now have 9 degrees, not -50.

Thanks to all who replied; it's great to be able to access such a breadth of information and advice.

Simon

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