Trailer Mode Won't Turn Off

[lardlad00]

Hey all -

I have a Model X with the towing package and it's giving me some trouble.

I have a little 4x8 utility trailer that I use once in a while to run for some lumber or whatever, but for the third time now, after going for a drive with it connected, trailer mode won't shut off when I disconnect the trailer. I can manually disable it but the yellow light stays on and must be re-disabled every time I get in.

The previous two times this has happened, I took it in for service and they replaced the rear body control module. The second time it happened they claim to have done a thorough checking of other wiring to make sure there was no other issue but they found nothing. They advised I check out my trailer to make sure there are no wiring issues on it.

So since then I've honestly been avoiding using the trailer as I haven't wanted to risk it. Tonight, though, I checked over the trailer wiring and replaced the 4-pin connector as it had been damaged since the last time I used it. Other than that it's basically a brand new trailer and wiring. I hooked it up and tested everything and it was working fine. I connected and disconnected it and trailer mode behaved as expected. So I then took it out for a 5-minute drive and of course, upon returning, trailer mode stayed on after I disconnected the trailer.

I'm feeling rather frustrated at this point. Even if there is a problem with my trailer somewhere that I haven't found, it seems like a mighty big design flaw that it could cause this control module to malfunction as it has. This is a simple trailer with basic tail lights, blinkers, etc. only, so worst case scenario would be a short somewhere, right? Shouldn't that be protected by a fuse at the very least?

At this point I'm not looking forward to dealing with getting it back for service (though it's due for regular maintenance so at least it won't be an extra trip). Anybody have any thoughts?

 

[boaterva]

How would the trailer cause the car to not know when it's disconnected? Either there's a lighting load on the circuit or there isn't.

Bjorn had this (see his recent summary of all the issues over 18 months with his P90D X) and I believe the SC couldn't solve it, either.

I would think the rear body control module would be the likely issue, whatever the trailer light harness plugs into. Does a reset of the MCU (normal scroll wheel reset) do anything to tell it to forget about the phantom trailer?

 

[vandacca]

It sometimes takes service 2-3 attempts to nail down the issue. I hate to say it, but taking it into Service is your only option.

 

[Zaphod]

Wonder if it is really just a software glitch instead of hardware issue. Does your trailer have LED lights? Have you tried a different trailer to see if issue can be pinpointed toward your X or something with the trailer itself?

 

[lardlad00]

How would the trailer cause the car to not know when it's disconnected? Either there's a lighting load on the circuit or there isn't.

My fear is that the trailer is shorting the module somehow and causing the malfunction. It does seem unlikely but I'm waiting for the service center to say that it's my trailer's fault and that I have to start paying for these module replacements.

Bjorn had this (see his recent summary of all the issues over 18 months with his P90D X) and I believe the SC couldn't solve it, either.

I hadn't seen that. His is the only other mention of this issue I've been able to find online but it sounds like it only happened to him once and was self-correcting.

I would think the rear body control module would be the likely issue, whatever the trailer light harness plugs into. Does a reset of the MCU (normal scroll wheel reset) do anything to tell it to forget about the phantom trailer?

I agree but to have it happen three different times makes me think there's either a different issue or a major glitch with the module. No combination of resets I have tried has changed anything.

It sometimes takes service 2-3 attempts to nail down the issue. I hate to say it, but taking it into Service is your only option.

I'm definitely going to do that next. Just hoping to make sure it gets full resolved eventually.

Wonder if it is really just a software glitch instead of hardware issue. Does your trailer have LED lights? Have you tried a different trailer to see if issue can be pinpointed toward your X or something with the trailer itself?

I do have LED lights. Perhaps the load is too small to trigger the module into turning trailer mode off? I don't have another trailer so I can't test, but the service center tested the new modules with their car trailers and found the module to be functional. Of course, I tried it in the shop with my trailer too and it worked fine. The problem seems to happen only after going for a drive or leaving the trailer connected for several minutes.

 

[vandacca]

I wonder if you need to add a resistor to the LED lights? I've heard of people needing to do that for RV trailers. Maybe something like this would work?

 

[LukasSwan]

I wonder if you need to add a resistor to the LED lights? I've heard of people needing to do that for RV trailers. Maybe something like this would work?

I have LED lights. I towed for months fine. Then one day trailer mode wouldn't turn off at all. And if I plugged my trailer in the left brake light stayed on all the time. Even when car was off. It was the module. They replaced it an all is well now.
Regardless of the trailer, your module should be smart/designed enough to handle any trailer misfits. If not, it was not comprehensive design.

 

[lardlad00]

So an interesting development: after using the trailer again a few days ago, trailer mode is back to operating normally.

I'm definitely suspecting that the LED lights have something to do with it.

I wonder if you need to add a resistor to the LED lights? I've heard of people needing to do that for RV trailers. Maybe something like this would work?

If it continues to be a problem I'm going to try something like that.

I have LED lights. I towed for months fine. Then one day trailer mode wouldn't turn off at all. And if I plugged my trailer in the left brake light stayed on all the time. Even when car was off. It was the module. They replaced it an all is well now.
Regardless of the trailer, your module should be smart/designed enough to handle any trailer misfits. If not, it was not comprehensive design.

That's really interesting to hear another similar experience. Mine works similarly where the lights stay on all the time when connected and trailer mode is not working properly.

Luckily it has resolved itself this time, but I'll dredge this post back up if it doesn't last.

 

[mudfud]

I am having similar issues

New model X has 7 pin receptacle. When I plugged my all LED My Pod trailer in, the lights first did not work. The trailer icon was not lit on dash.

While driving up 50, the yellow trailer icon lit and I was told to turn on trailer mode, which made the icon turn blue

Next check of trailer had ALL the lights lit. When I turned off the car, the lower running lights on trailer stayed lit. Had to unplug to turn off

I tried the resistive adapter mentioned in another thread, and this did not change anything.

Now the yellow trailer icon is always there and sometimes turns blue in its own. I turn it back to yellow with trailer mode off again.

Tesla mobile’s in the driveway now

Will update if I learn anything

 

[mudfud]

Tesla tech says that it looks like a bad control unit in the back. before he can "condemn" this module, he has to take the bumper off and check the wiring harness. He's supposed to return this afternoon, so more info to come.

 

[LukasSwan]

Tesla tech says that it looks like a bad control unit in the back. before he can "condemn" this module, he has to take the bumper off and check the wiring harness. He's supposed to return this afternoon, so more info to come.

It's only a few data points, but their control module seems to struggle with LED . So weird they stay on at 10% when the whole car is shut down

 

[mudfud]

Once I get the bad module, I plan to debug it with an electronics friend of mine. maybe we can suggest an iimprovement to their circuits.

 

[mudfud]

Still waiting for replacement module.

The yellow trailer icon is always on and sometimes it’s blue. Have to keep manually turningntrailer mode off.

Does anyone know if the trailer module can be unplugged for now? Auto pilot can’t be used while the trailer mode keeps turning on.

 

[XMan84]

Still waiting for replacement module.

The yellow trailer icon is always on and sometimes it’s blue. Have to keep manually turningntrailer mode off.

Does anyone know if the trailer module can be unplugged for now? Auto pilot can’t be used while the trailer mode keeps turning on.

Hi, did you manage to find the root cause for this issue? Thanks for your reply!

 

[Surcharge]

I’m having the same exact issue no trailer connected after towing something a few days ago yellow icon is still on screen sometimes it’s blue auto pilot cannot be activated unless I manually turn off trailer mode please let me know if you figured this out as my car is fully wrapped in vinyl and xpel I’d rather not have the service center remove the bumpers if not necessary

 

[Phil Seastrand]

I'm in the same boat. I plan to schedule a service visit soon to see what they say.

 

[ecarfan]

Just found this interesting thread, as for the past year and a half I have regularly towed a travel trailer with full LED but have never had the problem described here.

@Surcharge and @Phil Seastrand do you tow a full LED trailer? I suppose most modern trailers are only LED now.

 

[Phil Seastrand]

Definitely not an LED trailer.

 

[Surcharge]

I actually just towed a trailer that has not been touched since 2006 one of the lights definitely has an issue or rusted out I’m sure that might be the cause of this problem there should be some sort of short or fault protection though it seams a lot of people are having this issue

Does anybody know the difference between yellow and blue trailer icon

 

[ShawnA]

Hi Surcharge,

According the manual - Yellow: trailer/accessory is attached sensed by wiring harness connection - trailer mode "not" active.
Blue: trailer is attached sensed by wiring harness connection - trailer mode is "active."

Shawn