Not a big issue, but somewhat annoying ... my external temperature display no longer seems to be accurate. It used to hone in on the real ambient temperature within about a minute of pulling out of my garage, but lately it is VERY VERY slow to adjust and doesn't seem to ever reach the real outside temp. It's been over 100 degrees F for several weeks here in KC, but the display rarely gets over 90.

Before you ask if I'm looking at the internal temp, I'll assure you I know how to switch between the internal/external readings.

My first question is - where is the actual sensor? Can it go bad?

Thanks for any info you can provide!
Steve

 

The Ambient Air Temperature Sensor is mounted on the RH horn bracket which is on the bumper beam. You'll have to remove the bumper undertray to access it. This is what you're looking for:



It's a thermistor which sends a signal to the ACCM (Air Conditioning Control Module) to relay external temperature to the display. The signal is damped to give a more stable reading.

It could be physically damaged or dirty.

Graham

 

Graham, or anyone else, how fast does yours react?
The one on my S is very good, but the XK8 one is very slow, it will come to the correct temp eventually but takes a long time to adjust, this can be with a considerable temp swing from inside the garage to outside of 20 deg F or more.

 

Norri,

Seriously, think about it. When will I ever be likely to be able to test a 20 deg F temperature difference between the garage and outside!

Graham

 

Mmm, didn't consider that.
Maybe someone else who lives in hell will answer.

 

Mine reads instantaneously. Seems to be dead on. If they get water inside them they're toast.

 

Water in the harness contact or through a damaged body?

Graham

 

Mines accurate but it takes forever to get to the outside temperature after being in the garage ( usually my garage is twenty degrees below the outside temperature in the summer). Somewhere between fifteen minutes to twenty.

 

I had the same problem with my sensor. Slow and inaccurate temp. Reading, so I bought a new sensor, 75.00 and it was actually worse than the old one that had been on car since new. It was about 10 years old, so I figured that from where it is located up front under bumper that it was old and not working as well as it should be, so I bought the new one, it took at least 30 minutes to rise in temp from garage (garage temp 75 degrees , outside temp 106 degrees) and never got above 86 degrees.
What a waste of time and money.

Happy Motoring...

 

I guess it is normal then, probably designed for British weather.
I had a Chevy Silverado rental for a while and it was always right first thing in the morning, as I was driving around the site during the day (short trips 5/10mins) it never budged on the way back at night it would sort itself out after about 15mins.
This could be a huge change from morning to afternoon.

 

That's saved a lot of people wasting $75.00.
Graham

 

I would think, from where it is located, that it takes a while for the actual temperature to change at the sensor.
It would be interesting to put another sensor/thermometer in the same position and see how that compares?

 

I think I would have choked on the beer!
I've never changed the sensor on the S but those that have report it is cheap enough just to put a new one in order to eliminate it as a problem.
If I recall about 10 quid.

 

So, is the location of the sensor such that it might get wet from a high pressure car wash? I've been doing that lately, which is a change from my usual hand washing.

Like I mentioned my sensor was working fine prior to last month.

 

High pressure directed at the sensor is likely to get into the harness connector. it's waterproof but those lances deliver at some force.

Graham

 

Derek,

If I can encourage you to sit on the end of the bonnet with a thermometer whilst I drive, this would answer two questions:

1. is the external temperature accurate
2. does a bonnet mascot improve the appearance

Over to you.

Graham

 

I was meaning while stationary, but.....

If it ever stops raining I must get out and see where this sensor actually is!!

 

Has to be mobile. We've got to be scientific about this and take the wind chill factor into account.

Is it still down there? Glorious sunshine up here. Another 10 deg and I'll be able to take my overcoat off.

Graham

 

Mine will adjust over the course of a few minutes and seems to be more or less on par with my experience with other cars. Being in a relatively shielded location I wouldn't expect an instant change.

Over the last few days it's read things like 106, 109, 115F. Not quite in hell proper, but only a few streets over.



If your reading is consistently low, you might check the connections. I do not know whether these sensors have a positive or negative temperature coefficient but my guess would be negative, in which case a dirty contact will have a higher resistance, which makes a lower reading.

There appear to be two connectors in line, one at the sensor itself and the other at the left A pillar as part of the 20pin facia harness. The ground side of the signal also goes through the instrument panel harness, but this is shared with the inside temp sensor and blower controls, so probably isn't the problem if those other things work.

 

If you look at trickle charger thread on XK you will see I’m having trouble getting my heating to work at all after a jump start was needed because of low battery. Followed GGG tip for system reset but to no avail. So I can only conclude that ac and external sensor are linked and if default reading for sensor not working reading is -40C, then Also ac not going to work. So need to contact dealer.

Any other suggestions? It’s actually +2 C outside.