I've searched the forums and haven't seen anyone with this exact problem - it's a strange one. Hopefully someone here can help me figure this out...

Basically, whenever it rains my ambient air temp reading plummets. Today, for example, it dropped from 47 to -1 in the space of about 30 seconds when turning on the car after work. Once the temp reading drops it stays there, shooting from lows below zero to the teens or low 30s, then back down. After a night in the garage it will be fine. In fact, if the rain ends while I'm driving the sensor reading often returns to normal right away.

Now if all that happened was a bad reading I could ignore it. Once the ambient temps drop below 10 degrees or so it seems like the heating system starts to recirculate aggressively, making the car eventually fog up. Of course, the fogging could be from water getting in to the system somewhere as well.

All other AC and heat functions work fine. I've replaced the ambient air temp sensor and inspected the wiring harness area in the front of the car - it seems to stay dry. There are no other obvious wet spots immediately visible under the hood.

Any ideas? Has anyone else had something like this happen? My car is a 2005 STR with about 60k miles.

 

Could it be that the rain is cold and affecting the sensor?

 

I don't think so. I moved the sensor to a spot above the normal mount point and wrapped the housing and visible wires with electrical tape to prevent moisture from entering. Still happening.

I suspect a cracked insulator somewhere in the wiring that's shorting in the wet. I hope that's not it, since that seems like it could be very difficult to track down and fix.

 

Perhaps a re-set of power to the temp. control module will re-set its parameters?

 

Worth a shot. Unfortunately I don't know how to do that, other than disconnect the battery. Is there a better way?

 

Actually periodic hard-resets of the ECU, etc. does wonders for the STR. I hard-reset my 03 STR every now and then and she responds marvelously with thinner fuel trims and more lead in ignition timing. Aside from clearing resolved fault messages, incorrectly stored data within modules, adaptive learning is cleared making way for fresh driver input.

 

My oneline is for a 2004 not 2005 so forgive me if I am off track.
Looking at the 2004 oneline it shows two things that I feel may be worth checking and they are the ambient temperature and the humidity sensor. Your problem seems to be when it rains and your ambient sensor or connectors may become contaminated with water intrusion providing a bad reading. The humidity sensor could not be sensing the humidity properly when it is raining. Just a thought and I hope it helps!

 

bfsgross, how do you do the hard reset of the ECU? You guys are a wealth of information. Thank you.

 

The electrical guide shows the connectors & splices and sometimes their location, if you need to go that way. See Jaguar electrical reference

The ext sensor is quite cheap and may be worth changing in the hope it's faulty.

The humidity sensor is inside the cabin I believe so I don't see how it can be that.

 

My theory was that when it rains the humidity changes drastically and that change could make a difference. Just a theory!

 

does your car have the auto wiper feature. I don't know how the two could be related, but the auto wiper feature is very sensitive to rain. Just a thought. Good luck

 

I replaced and relocated the sensor already and I still see the problem, so that's unlikely to be the culprit.

That said, after the comments in this thread I'm thinking I may have a crack in the socket the around the sensor that's letting moisture in. I'll take a look at it tonight. If that doesn't show promise it's off to the electrical guide...

Thanks to everyone for the tips!

 

Sounds possible. (Don't know if it happens, though.)

 

Hmmm... I realize this is an old thread, but disappointed it never came to resolution, as I have the identical problem. I guess I'll try a battery reset first, then replace the ambient temp sensor if that doesn't work.