This may fix your outside temperature display if faulty

**Adrian** · by **Adrian** » Fri Sep 04, 2009 6:15 pm

My dual display digital temperature readout has been showing way too high a temperature for a long time and I decided to try and fix it. I though £15 for a new sensor was too steep so I started messing around with the old one (guessing that this was the problem) - and in the process got it working properly again! BTW, the sensor is located under the front bumper on the nearside - it actually goes through the bumper so you should see it and pop it out quite easily.

This is how it went: I decided to measure the sensor's resistance to see how it changed with temperature and compare the figures with typical sensors of the same type to see if this really was the problem. To get a straight-line plot of temperature vs. resistance involves steam (for accurate 100'C) and melting ice (for accurate 0'C). Remember - before I did these measurements the sensor was reading way too high. But after boiling and freezing, something magic happened - it works fine again!

I can rule out bad connections because before I did the two-point test I checked the resistance of the sensor, off the car, at room temperature - and after the heat stressing this changed significantly. I'm thinking that the crystalline structure of the sensor slowly changed over the years and a bit of thermal stress got it back to normal. Anyway, I thought I'd post this as it's a doddle to do and when I searched before I couldn't find anything other than "buy a new one".

Callyman · by **Callyman** » Fri Sep 04, 2009 6:40 pm

Mine was playing up big time, so i replaced it with a new one, and it's still the same. Must be a wiring fault somewhere.

**Adrian** · by **Adrian** » Fri Sep 04, 2009 9:04 pm

callyman - if your sensor is definitely OK then I'd be checking the terminals of the plug that goes into it and more so the plug that goes into the display unit. The 0.1" pin headers on the display board tend to oxidise and the amount of current flowing into the sensor is absolutely minute so any resistance here will throw the readings. Connectors like these ought to be gold-flashed but they aren't. You can clean the pins quite well with a metal polish like Brasso on a cotton bud. You can also dab a bit of copper grease on the pins to prevent them oxidising again - but this stuff conducts - so don't go bananas with it!

Callyman · by **Callyman** » Fri Sep 04, 2009 10:35 pm

Will try that. Thanks for the tip.

**frankej** · by **frankej** » Sat Sep 05, 2009 12:45 am

Adrian wrote:the sensor is located under the front bumper on the nearside

mine is hanging out loose below my bumper

dont know where it clips into :think:

**Adrian** · by **Adrian** » Sat Sep 05, 2009 9:19 am

frankej wrote:mine is hanging out loose below my bumper dont know where it clips into

It can't be far from the hole - the wiring loom isn't all that long where it branches off to the sensor. It's quite close to the nearside.

**Adrian** · by **Adrian** » Sun Jan 16, 2011 5:01 pm

Just thought I'd update this thread: Over a year now and it still works perfectly. The original "fix" after taking the sensor to 100'C and 0'C turned out to be only temporary so at the beginning of last year I tried again but this time alternately heating and cooling the sensor in quick succession using a hair dryer and a can of freezer aerosol. As these parts get harder to get hold of I hope this info may be of help to someone someday

This may fix your outside temperature display if faulty