Mystery to Solve! Temp and Parking Sensor Failure after heavy rain or car wash...

[FMinMI]

So I have a mystery with my 12/2016 build 75D MS that is driving me crazy and hope there are some good detectives here on the forum to solve it.

For the last year, I have had my external temp sensor temporarily go from the current/correct temp to -40F and then to "---". This happens every time I drive through a very hard downpour or go through our local Mister Car Wash. In addition to the temp not being correct, I will get "Parking Assist Unavailable", with the latter only happening when the temp is showing the "---"; if the temp changes to any other value (even -39F), that error does not appear. Now, if it is warm outside, and I park the car in the sun, in about 2-6 hours the temp sensor will work correctly when the car is turn on (of interest is that when the car is off, the temp is actually correct!). During the winter months, it can take several days for the temp sensor to read correctly - sometimes after a day in my partially heated garage it would maybe be off by 10 F or so, then finally be right. And BTW, when I would go into service mode and look at the ultrasonic sensors, they were all "green".

So, the first thing I thought was the problem was the temp sensor itself and somehow it was shorting out the parking sensors, so I replaced it, and at the same time, checked every connection that is on the front fascia (all 6 parking sensors and the air quality check sensor, which is on the opposite side of the temp sensor), also applying a light coating of dielectric grease to each connection. It did not correct the problem.

Then I thought maybe there was a bad ultrasonic sensor that was causing the temp sensor to short out, so I decided to, one by one, flood each sensor with water for 5 minutes, then checked to see if the temp screwed up. Nothing happened - my temperature continued to read correct. But the next time I went through the car wash - it failed again :-(

My next test was before going through the car wash (and the temp sensor was reading correctly), I taped over all 6 ultrasonic sensors as well as the temp sensor and the air quality sensor just to confirm they were not the culprit. I still had the problem.

Now here is where it get interesting. After that last test, I decided to flood the front windshield with a lot of water. That DID cause the problem to materialize, and after a few days of drying out and testing again, I found that flooding the passenger side of the window area caused the problem but not if I did the same thing to the drivers side. So there is something happening on the passenger side.

And here is the most bizarre finding to date. After confirming for the 3rd time that flooding the passenger side of the window 'creates' the problem, I went for a drive. As before, before starting the car the temp showed correct but as soon as I pressed the brake to start the car, it then started to fall from 50F all the way down to -40F and finally "---". But then I noticed it change from "---" to -30F and then back up. Why? I made a RIGHT turn! When I then started going straight, it slowly went back to -40F and "---". So I decided to make another right turn. Same results! So off a parking lot I went. Guess what. When I went in a clockwise circle, I could get the temp to start going up from -40F to slightly positive (remember, it is 50F outside at this point). As soon as I changed to counterclockwise, it dropped unbelievably fast to "---"

So, what I can only guess, water is pooling somewhere on the right / passenger side of the car under the hood (?), and there is either a sensor, connector or damaged wire bundle that is somehow sitting/laying in the place where the water can pool.

My question - does anyone have any idea where to look???

Any suggestions would be GREATLY appreciated!

Thanks!!!

 

[NewbyMaybe]

So I have a mystery with my 12/2016 build 75D MS that is driving me crazy and hope there are some good detectives here on the forum to solve it.

For the last year, I have had my external temp sensor temporarily go from the current/correct temp to -40F and then to "---". This happens every time I drive through a very hard downpour or go through our local Mister Car Wash. In addition to the temp not being correct, I will get "Parking Assist Unavailable", with the latter only happening when the temp is showing the "---"; if the temp changes to any other value (even -39F), that error does not appear. Now, if it is warm outside, and I park the car in the sun, in about 2-6 hours the temp sensor will work correctly when the car is turn on (of interest is that when the car is off, the temp is actually correct!). During the winter months, it can take several days for the temp sensor to read correctly - sometimes after a day in my partially heated garage it would maybe be off by 10 F or so, then finally be right. And BTW, when I would go into service mode and look at the ultrasonic sensors, they were all "green".

So, the first thing I thought was the problem was the temp sensor itself and somehow it was shorting out the parking sensors, so I replaced it, and at the same time, checked every connection that is on the front fascia (all 6 parking sensors and the air quality check sensor, which is on the opposite side of the temp sensor), also applying a light coating of dielectric grease to each connection. It did not correct the problem.

Then I thought maybe there was a bad ultrasonic sensor that was causing the temp sensor to short out, so I decided to, one by one, flood each sensor with water for 5 minutes, then checked to see if the temp screwed up. Nothing happened - my temperature continued to read correct. But the next time I went through the car wash - it failed again :-(

My next test was before going through the car wash (and the temp sensor was reading correctly), I taped over all 6 ultrasonic sensors as well as the temp sensor and the air quality sensor just to confirm they were not the culprit. I still had the problem.

Now here is where it get interesting. After that last test, I decided to flood the front windshield with a lot of water. That DID cause the problem to materialize, and after a few days of drying out and testing again, I found that flooding the passenger side of the window area caused the problem but not if I did the same thing to the drivers side. So there is something happening on the passenger side.

And here is the most bizarre finding to date. After confirming for the 3rd time that flooding the passenger side of the window 'creates' the problem, I went for a drive. As before, before starting the car the temp showed correct but as soon as I pressed the brake to start the car, it then started to fall from 50F all the way down to -40F and finally "---". But then I noticed it change from "---" to -30F and then back up. Why? I made a RIGHT turn! When I then started going straight, it slowly went back to -40F and "---". So I decided to make another right turn. Same results! So off a parking lot I went. Guess what. When I went in a clockwise circle, I could get the temp to start going up from -40F to slightly positive (remember, it is 50F outside at this point). As soon as I changed to counterclockwise, it dropped unbelievably fast to "---"

So, what I can only guess, water is pooling somewhere on the right / passenger side of the car under the hood (?), and there is either a sensor, connector or damaged wire bundle that is somehow sitting/laying in the place where the water can pool.

My question - does anyone have any idea where to look???

Any suggestions would be GREATLY appreciated!

Thanks!!!

 

[NewbyMaybe]

There's a ground post on the frame work under the frunk, passenger side. If it's loose then the cornering might be tweaking the harness. If that's not it I would definitely order a new flux capacitor.

 

[FMinMI]

There's a ground post on the frame work under the frunk, passenger side. If it's loose then the cornering might be tweaking the harness. If that's not it I would definitely order a new flux capacitor.

Seems odd that it wouldn't flex (and cause the 'failure') when making a turn in both directions but at this point in time I will check out anything to fix the problem. Adding it to my list. Hopefully will get several more suggestions before I start tearing the front apart...

Thanks.

 

[NewbyMaybe]

Hopefully it's not rodent damage. The little buggars might be rolling around in a nest and hitting a freshly chomped wire.

 

[FMinMI]

Hopefully it's not rodent damage. The little buggars might be rolling around in a nest and hitting a freshly chomped wire.

I am 99% sure it is not. The car is always stored in the garage, and the garage door is always kept closed. There is also dog and cat food stored right next to the car (plus in the winter, some stuff like bread, potatoes, etc) and they have never shown any damage from varmints. I am retired so it is not parked at a work location for hours, and when I do go somewhere very seldom do I leave it unattended for more than a couple hours, and that's during the day only.

 

[KalJoMoS]

There is the front harness connector (the one for the parking sensors and front radar/temp.sensor) on the passenger side, behind the wheel liner right next to the front light, in the front “engine bay”. Is it possible that some harness there are somehow binded and each time you turn the wheel it will have the effect on this connector. There is quite distance thought from the steering rack, but as already mentioned on the same panel, inside the bay there is the ground post as well.
Looking for the result as I have few times seen my temperature to be odd on startup, but only to a freezing value while outside is actually on warmer side.

 

[rlsd]

I am 99% sure it is not. The car is always stored in the garage, and the garage door is always kept closed. There is also dog and cat food stored right next to the car (plus in the winter, some stuff like bread, potatoes, etc) and they have never shown any damage from varmints. I am retired so it is not parked at a work location for hours, and when I do go somewhere very seldom do I leave it unattended for more than a couple hours, and that's during the day only.

Rats can get in your car when you park your car in public places.
I put D-con in my garage to kill rats. One day I saw a dead rat under the car hood. The rat was lying on a nest built with D-con.
Probably EV cars have less problems with rats because rats tend to get in the warm ICE cars during the winter.

 

[FMinMI]

Rats can get in your car when you park your car in public places.
I put D-con in my garage to kill rats. One day I saw a dead rat under the car hood. The rat was lying on a nest built with D-con.
Probably EV cars have less problems with rats because rats tend to get in the warm ICE cars during the winter.

Yesterday I flooded the passenger side window and got it to fail. I then disassembled the entire front. I found no damaged wires anywhere. I also found two cable bundles that were soaking wet. I found no connectors wet. So I let it dry completely, then used a hair dryer to further dry them out. Then I put a waterproof foam cover over those two cables in the area where they got wet. I also checked all 4 connectors bolted to the frame where the temp and parking sensors route through. They were all seated / connected and dry, but I still put a little dielectric grease on them and made sure they were locked in place. This morning I flooded that area and am waiting to see if the problem is fixed. But I am doubtful, as the 'turning' observation, which I was able to repeat multiple times, wouldn't have been impacted by where these cable bundles were at.

Thanks for the reply.

 

[FMinMI]

There is the front harness connector (the one for the parking sensors and front radar/temp.sensor) on the passenger side, behind the wheel liner right next to the front light, in the front “engine bay”. Is it possible that some harness there are somehow binded and each time you turn the wheel it will have the effect on this connector. There is quite distance thought from the steering rack, but as already mentioned on the same panel, inside the bay there is the ground post as well.
Looking for the result as I have few times seen my temperature to be odd on startup, but only to a freezing value while outside is actually on warmer side.

Yesterday I disassembled the entire front. I found two cable bundles that were soaking wet and those are the bundles that carry the sensor and temp wires. I found no connectors wet including the 4 that you are talking about (I think the sensors connect through the top one). I let it all dry completely, then used a hair dryer to further dry those bundles out. Then I put a waterproof foam cover over those two cables in the area where they got wet. As for the connectors, I released and reconnected them, and put a little dielectric grease on them as well. This morning I flooded that area and am waiting to see if the problem is fixed. But I am doubtful, as the 'turning' observation, which I was able to repeat multiple times, wouldn't have been impacted by where these cable bundles were at.

Fingers crossed. Thanks for the reply.

 

[DAN60]

FMinMI, I live in the UK and drive the same age S75D. I developed the same exterior temperature gauge readings/ failure along side the Parking assist unavailable in exactly the way you described it about 2 months ago. It was sporadic to start with and is now a definitive "---" and "parking assist unavailable" on every journey. When I pulled up the active alerts data from the service menu it comes up with:
THC_d0020_ RCCMTempSnsAmb (service fix) and
PM_w041_dasMIA (service fix)

Where things differ is that I haven't been through any car washes or had much access to potential flooding. I also have no changes in symptoms with manoeuvring the car, as you described, turning left and right in tight turns. There doesn't appear to be any "drying out" improvements.

My car lives in a dehumidified garage during the night and in a covered public car park during the day. We've had the usual UK weather but nothing abnormal. I also wash my car, in the same way I have for the past 6 years.

I have had my service request logged with Tesla for the past 6 weeks but they are being very slow in getting back to me. I call them every week for an update and request to get my car in for a service repair but to no improvement. I get the feeling that the local UK service boys don't know how to resolve this fix.

Do you have any update on the situation and considering the exact similarity in symptoms and age/model of car, is there a software glitch here?

 

[FMinMI]

FMinMI, I live in the UK and drive the same age S75D. I developed the same exterior temperature gauge readings/ failure along side the Parking assist unavailable in exactly the way you described it about 2 months ago. It was sporadic to start with and is now a definitive "---" and "parking assist unavailable" on every journey. When I pulled up the active alerts data from the service menu it comes up with:
THC_d0020_ RCCMTempSnsAmb (service fix) and
PM_w041_dasMIA (service fix)

Where things differ is that I haven't been through any car washes or had much access to potential flooding. I also have no changes in symptoms with manoeuvring the car, as you described, turning left and right in tight turns. There doesn't appear to be any "drying out" improvements.

My car lives in a dehumidified garage during the night and in a covered public car park during the day. We've had the usual UK weather but nothing abnormal. I also wash my car, in the same way I have for the past 6 years.

I have had my service request logged with Tesla for the past 6 weeks but they are being very slow in getting back to me. I call them every week for an update and request to get my car in for a service repair but to no improvement. I get the feeling that the local UK service boys don't know how to resolve this fix.

Do you have any update on the situation and considering the exact similarity in symptoms and age/model of car, is there a software glitch here?

TEH75D,

So after covering those 2 cable bundles with foam and running my car though the car wash twice on consecutive days, I thought I fixed it - the temp continued to read correctly. But to be sure, on that second day, I came home and did a supersoaking of water on the passenger side (full stream garden hose for at least 3 minutes - had to be 100 gallons or more of water) and unfortunately, the problem came back, BUT it was not as bad as previously, with my temp going down about 20 degrees F (was 50, was showing 30s). I still observed the right turn/left turn mystery however. And it did clear up the next day, with the car sitting in a 50F garage.

I have a mobile tech coming Wednesday and I plan to bring it up with him. Since I believe I was very thorough when I took the front end apart and found no wires/connectors sitting in a place where water was collecting (and could explain the left/right turn mystery - my thinking is that a connector was sitting in a tray and the water was caught there moving over that connector sitting in the tray with turns), I now wonder if somehow water is getting INTO the car (from below the window?) and finding its way to the passenger side floor area and collecting, and that there is a connector there that is getting wet. They did replace my window a couple of years ago. But that logic wouldn't explain why covering the cable bundles lessened the temperature change impact (they were not located by or going into the firewall) unless somehow the water is being routed through the cable bundle and into the car. But then again, where the bundle got wet is below the level of the massive rubber gasket where it goes into the car and is now covered :-(

I will post Thursday what, if anything, he thinks. And when you get your appointment, please do the same.

Cheers.

 

[DAN60]

TEH75D,

So after covering those 2 cable bundles with foam and running my car though the car wash twice on consecutive days, I thought I fixed it - the temp continued to read correctly. But to be sure, on that second day, I came home and did a supersoaking of water on the passenger side (full stream garden hose for at least 3 minutes - had to be 100 gallons or more of water) and unfortunately, the problem came back, BUT it was not as bad as previously, with my temp going down about 20 degrees F (was 50, was showing 30s). I still observed the right turn/left turn mystery however. And it did clear up the next day, with the car sitting in a 50F garage.

I have a mobile tech coming Wednesday and I plan to bring it up with him. Since I believe I was very thorough when I took the front end apart and found no wires/connectors sitting in a place where water was collecting (and could explain the left/right turn mystery - my thinking is that a connector was sitting in a tray and the water was caught there moving over that connector sitting in the tray with turns), I now wonder if somehow water is getting INTO the car (from below the window?) and finding its way to the passenger side floor area and collecting, and that there is a connector there that is getting wet. They did replace my window a couple of years ago. But that logic wouldn't explain why covering the cable bundles lessened the temperature change impact (they were not located by or going into the firewall) unless somehow the water is being routed through the cable bundle and into the car. But then again, where the bundle got wet is below the level of the massive rubber gasket where it goes into the car and is now covered :-(

I will post Thursday what, if anything, he thinks. And when you get your appointment, please do the same.

Cheers.

I have been back to the Winchester (UK) branch for an update on getting the car in for the service department to try and resolve the symptoms. Sadly they are declining to have the car, reporting that they are waiting for their technician to get a diagnosis from the symptoms first. This is now nearly a month of no temperature and auto park failure, which is annoying. I am getting no closer to a solution.
Have you had any joy that I might be able to report back to the UK boys?

 

[FMinMI]

I have been back to the Winchester (UK) branch for an update on getting the car in for the service department to try and resolve the symptoms. Sadly they are declining to have the car, reporting that they are waiting for their technician to get a diagnosis from the symptoms first. This is now nearly a month of no temperature and auto park failure, which is annoying. I am getting no closer to a solution.
Have you had any joy that I might be able to report back to the UK boys?

My mobile appointment was changed to a service center one because one of the problems required the charger port to be replaced, and that can only be done at the service center by a trained tech (due to high voltage). It went in last Thursday and they still have due to lack of parts. I asked them to look into the intermittent temp/parking sensor issue when I took it in but they said 'if they get time'. :-(

Will LYK if they get back to me with what it is.

Frank

 

[DAN60]

My mobile appointment was changed to a service center one because one of the problems required the charger port to be replaced, and that can only be done at the service center by a trained tech (due to high voltage). It went in last Thursday and they still have due to lack of parts. I asked them to look into the intermittent temp/parking sensor issue when I took it in but they said 'if they get time'. :-(

Will LYK if they get back to me with what it is.

Frank

I have been to the Winchester service centre today and have had my car repaired. The temperature sensor is now working and correct, the autopark warned is off and the function is working well. I am pleased report that the car is back to full function again!
The technician notes:
Removed front fascia
Inspect harness
Installed replacement harness
Reinstalled fascia
Tested part assist
External temp displaying correctly on dash also

It appears that it was the wiring harness at fault and once replaced the external temperature sensor was fine. This also corrected the autopark issue.

I wish you the best of luck with getting your wiring harness changed and your problems being resolved too
Toby

 

[FMinMI]

I have been to the Winchester service centre today and have had my car repaired. The temperature sensor is now working and correct, the autopark warned is off and the function is working well. I am pleased report that the car is back to full function again!
The technician notes:
Removed front fascia
Inspect harness
Installed replacement harness
Reinstalled fascia
Tested part assist
External temp displaying correctly on dash also

It appears that it was the wiring harness at fault and once replaced the external temperature sensor was fine. This also corrected the autopark issue.

I wish you the best of luck with getting your wiring harness changed and your problems being resolved too
Toby

Hi Toby,

Can you tell me which harness they replaced? Maybe there is a part number on your invoice? And what was the cost if I may ask?

I'd like to see if that harness is anywhere near the passenger side front windscreen.

Thank you

 

[DAN60]

Hi Toby,

Can you tell me which harness they replaced? Maybe there is a part number on your invoice? And what was the cost if I may ask?

I'd like to see if that harness is anywhere near the passenger side front windscreen.

Thank you

The part number was: ASY,HRN, MDLS, ALL, BUMP FR, DA01 (1004420-04-T)
The cost was £160 including all tax for the part. £100 for the labour.
They had to take the front facia off but no further details for the location of the harness.

 

[KalJoMoS]

It’s a front harness for the USS and radar unit with the temperature sensor. It starts right behind RH front light, it is the wire that needs to be unplugged if you remove the bumper. See photo, connections marked by red arrow and harness by green line.

 

[FMinMI]

Hi Toby,

Can you tell me which harness they replaced? Maybe there is a part number on your invoice? And what was the cost if I may ask?

I'd like to see if that harness is anywhere near the passenger side front windscreen.

The part number was: ASY,HRN, MDLS, ALL, BUMP FR, DA01 (1004420-04-T)
The cost was £160 including all tax for the part. £100 for the labour.
They had to take the front facia off but no further details for the location of the harness.

OK. Thank you. I will look up the part number and check it out on my car but I am thinking it won't be my problem since the way I get it to fail is pouring lots of water down the front windscreen on the passenger's side. After I did that and tore my frunk apart and checked this area (front fascia) it was not wet at all. And I also wonder if there are differences between LH and RH steering MSs.

Cheers!

 

[FMinMI]

It’s a front harness for the USS and radar unit with the temperature sensor. It starts right behind RH front light, it is the wire that needs to be unplugged if you remove the bumper. See photo, connections marked by red arrow and harness by green line.

View attachment 938901

Thanks for the photo and illustration. What year is this? It looks a lot different than my 2016.5 MS. Not sure if this is older or if there are differences due to RH and LH steering. That cable coming from the front fascia on mine comes to a 'block' of four connectors on the inside of the passenger side frame...