My external temperature reading has been showing +49.5 Degrees Centigrade since I got the car about a month before Xmas. So today I decided to investigate and removed the sensor from behind the grill. The plastic cover was broken on it and the wires to the sensor on the tip exposed. With it plugged out, I was now reading -40
So took it as a fair bet that it was the sensor that was at fault I cut one of the exposed wires and soldered in a 4.7Kohm
resister in series. It was reading 700 Ohms on its own. It was now reading 28 Degrees Centigrade
So cut the two legs and soldered in 2 x 5.6 KOhm and tried again and now reading +8 Degrees Centigrade.

New Sensor Ordered

It does seem strange how almost all car thermometers read artificially high at least by 1 or 2 degrees.I have a couple of more accurate ones at home and the usual hot or cold days when people say it is [x] degrees today after driving their car when I usually have to correct them !

Anyone got any idea why this AAT sensor has now started reading - 40.
I disconnected the battery today to just change a Fog bulb and a harness check.
On restarting the car noticed the ambient air temp reading was -40.
To the best of my knowledge I have not disturbed this sensor.
Is this just a coincidence or can anyone think of a logical reason for this happening. Eddie the eagle watch out 👀

easy to check the wiring to the sensor as it sits behind the front grill. 3 screws to take it off and have a look. sounds like its open circuit. There is nothing that can't be fixed with a hammer😜😜
FFRR 4.4 SDV8 Autobiography Santorini Black.
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2010 LR D4 Commercial 2.7 TDV6

If nothing has been disturbed then do a hard battery reset... Might just put things right?

Mine read -40 withe the sensor unplugged.

Oups post by accident Eddie the eagle watch out 👀

Last edited by Pepi on 31st Jan 2016 2:29pm. Edited 1 time in total

Hi chaps
Thanks all. Can you tell me what route the harnes takes and where the loom connections are. What should the resistance be at say 14deg c. Has any one got any idea or a method of testing the sensor.
Also could this ambiant air temp sensor effect mixture control in ECU by richening the mixture when cold.
It just seems strange that since this fault has occurred the consumption has increased (markedly less MPG)
All of a sudden some weirded and wonderful thing happening for no apparent reason. Battery is charged and in good condition and output voltage and charging circut is all OK. No errors whistles or bells showing. Apart from a faulty N/S Fog light wiring fault. ECU box is clean dry and all connect is seem to be firmly attached.
So if any of you wizards out there can shed some light on probable cause it would be deemed a great favour to a poor and distressed man. That's now bloody cold and wet!!!!
😏 Eddie the eagle watch out 👀

Cheers Craig. Yep tried that. In fact it was working OK before I took the Battery off to charge it on the bench. I only did that because the car was not getting used much. I was getting between 20 to 23.5 mpg out of her on a steady motorway run to Wales and back at Christmas. Now it's down to 11.5 mpg. I know it may take a few miles to settle after a reset but not sure I can find Petrol stations close enough together to do that. LOL.
Is there a connector in the engine bay where I can isolate the sensor by unplugging it and bridge the connector with a resistor. If so what size resistor do I need to give me a bench mark instrument cluster display say mid range Zero degrees C.
Thinking being, that then it would narrow down the problem. It would also be interesting to see what effect if any it had on the MPG. Eddie the eagle watch out 👀

Last edited by Pepi on 1st Feb 2016 12:43am. Edited 2 times in total

Pepi,
For info on resistance on sensor read my first post.

Cheers Declan have read your post with interest. Did you find a resistor that would give you a zero reading? Or any LR written calibration data. Saying what resistance the sensor should be giving. Also did you try a dead short test reading.
The thing is that if I knew what the sensor should be giving then I can check for resistance faults in the remaining components after it has been taken out of the equation. Eddie the eagle watch out 👀

Hi Pepi,
No I didn't go any further with testing. All I was after was to see if varying the resistance gave me different readings. The theory was that if the circuit was sensing those variations it would pretty much proving that the sensor itself that was the faulty component. After all, its simply a variable resistor that is temperature sensitive.
No I didn't put a short on it simply because with the sensor plugged in and reading 700 Ohms I was getting max temp reading of 49.5 degrees and with it plugged out was getting -40 (min reading). Wouldn't advise to ever place a short on a electronic cct unless you are sure that is within its normal working range.
As above
700 Ohms read +49.5 / 50 (max reading so higher value could give same reading)
4.7 K-Ohm read +28 Celsius
11.2 K-Ohm read +8 Celsius (Extra 6.2 K dropped temp by 20 Celsius)
I would figure from that approx 13.6 K-Ohm would read around Zero
I didn't have a POT that I could solder in, but if you had, then easy to vary the resistance in cct and see if you vary reading on dash.
Afraid, I don't know where the physical wiring loom goes, as I didn't have to pursue it any further.

Declan

Had something similar last thurs when I changed the battery. Immediately showed as reading minus 40c !! Drove around for a couple of hours and the temp returned to what it should be, dropping a few degrees at a time.

Thanks Declan
Regards
Pete Eddie the eagle watch out 👀

Last edited by Pepi on 1st Feb 2016 8:10pm. Edited 1 time in total

Thanks for that it will be good to see if it will sort it's self on mine.
Did you notice an increase in consumption? Eddie the eagle watch out 👀