External temperature gauge fault

[rooted]

Hi, can anyone point me towards a cure for the fault on my '94 W124 E280's outside temperature gauge?

When I first turn on the ignition, the temperature display reads correctly. After starting up and running for between five to ten seconds, the display flashes and drops to about half the previous value, i.e. if it started at 17 degrees, it will go to 8.5. It will then continue to drop over the next couple of minutes, so even if the true outside temperature is about 17 degrees, the display will show only 3.5 or thereabouts.

I've tried to get at the sensor but it seems to be entombed in the foam in the front bumper (though I haven't taken the bumper off). I'm wondering if it's more likely to be a relay, or the gauge itself?

As the winter approaches, I thought it would be handy to know when it really was freezing. I suppose could always open the window...

 

[television]

This fault is normally the sensor its self and as you say it is behind the bumper, this is the first that I have that it is embedded in foam,it should not be.

Welcome to the forum

 

[rooted]

Thanks - I suspect I'll need to take the bumper off to have a proper look. I just followed, by touch, what I thought was the correct cable and that's where it disappeared.

 

[BlackC55]

No need to remove the bumper. Just take the under tray off and pull it hard to remove it.

 

[grober]

Later displays have an input from a road speed hall sensor to provide a correction factor for the car's movement thro the air The temperature displayed when the engine is first started may not be a true reflection of the outside temp till about 5 minutes have past and the car reaches speeds of at least 20-60kmph. Try that and see if you get a good temp readout. Otherwise I think your temperature readout unit is probably faulty. The other possibility is some form of voltage supply instability. Are all the other instruments indicating OK ?

 

[rooted]

Thanks to you all for your advice. Further poking around behind the bumper revealed that only the cable is buried in the foam; the sensor is screwed to the front of the bumper, behind the bottom edge of the number plate. I've kept an eye on the reading overseveral miles/minutes, and once it's dropped to the low reading, it stays there. All the other instruments read correctly.

 

[rooted]

For anyone else whose car has the same fault, I thought I'd mention the cure I found. Went through all the fuses in the box, cleaned the ends with sandpaper and the correct outside temperature reading returned.

Funny how it's sometimes the simplest things that make the difference...

 

[television]

For anyone else whose car has the same fault, I thought I'd mention the cure I found. Went through all the fuses in the box, cleaned the ends with sandpaper and the correct outside temperature reading returned.

Funny how it's sometimes the simplest things that make the difference...

Pleased that you solved the fault,, but one little thing, sand paper should not be used as these things are only flash nyckel plated.. Sanding can give high spots, though it may solve your problem it could do damage later through heat. You would be better off now in getting some non drying switch cleaner (Maplins) and spraying the fuses and socket contacts to keep moisture out and off. this will be a lasting long term fix.

I hope that you did not mind me saying