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Power Limited - Please Schedule Service - Potentially Trailer Mode Related?

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Brave Ulysses

Member
Apr 1, 2018
214
182
Denver
#1
This past Saturday I was suppose to head out on a 600 Mile roundtrip camping trip to Southern Colorado with my Model X and my teardrop camper. Got all our stuff loaded and the family loaded and then pulling out of my garage the Tesla flashed several warnings..... Braking Limited, Traction Control Disabled, etc.... I've had these pop up several times in the past month, but have been able to clear them with a reset. I reset, and they were still there. Reset again, some cleared, others didnt, reset again, seemed fine.... drove a few hundred feet, and then Power Limited - Please Schedule Service came on.

*sugar*......

For the next 5 hours I tried troubleshooting the issues myself and also called Roadside Service. Roadside Service was very helpful and tried to be as accommodating as possible but I learned that they really don't know how to troubleshoot an issue that could potentially be related to Trailer Mode. I did my best to search online for any signs of trailer mode triggering these warnings and came up empty.

The weird thing is the error messages remained with the trailer unplugged. So I couldn't isolate the problem to being electrical related to the 7 pin adapter. The one thing I did not try until 3 hours into this was unhitching the trailer. Tesla roadside service never suggested doing that either. it seems that only after unhitching the trailer and not having weight on the hitch ball, that the error messages would go away and trailer mode would officially reset.

I tested this several different times and in several different sequences and it seems more like the error messages are related to weight on the trailer ball, and less so the 7 pin connector.... but I honestly don't really know.


We had to abandon our trip which really sucked but I just couldn't risk this actually being a problem somewhere out in the rockies. I was fortunate it was on my block.

I drove the car the rest of the weekend without issue, actually did 250 miles roundtrip on Sunday and no warning messages, no performance issues.

I dropped the car off Tuesday morning at the service center and they have been trying to diagnose the problem since. Unfortunately, it seems like they are not having much success.


Does anyone have any ideas or similar experiences?


FYI, it's a 2018 Model X 100D (September 2018 build). And the trailer is a Dutchman T@b Trailer that I have customized and is approximately 1,650 pounds. I have never had an issue towing it before.


Prior to these problems, I was having a very glitchy month with the car with many computer crashes/resets/slow computer performance, and some MCU crashes when shifting the car into reverse.... I just chalked it up to a buggy software build but now im not sure.
 
#3
I’m not a tech guy, but I think they would have a hard time replicating the problem without a trailer with similar tongue weight as yours. I had a rattle in a BMW Z4 I used to have. I took it to my local dealer and they “couldn’t” replicate it. I took the car home, but realized that the tech probably never drove it since it rattled all the time. I took it back the next day and told them I was going to take the tech for a ride. I took him on a twisty rural road at about 105mph and asked, “Hear that rattle?” We both thought it was coming from the convertible hardtop. The dealer was too small to have the jig for a repair so I took it to the selling dealer 200 miles south. It wasn’t the top, it was an improperly installed amplifier in the trunk. LOL
 
#4
When you first posted (before you mentioned unweighting the hitch) I was thinking it's the 12V battery. Just before failure they are known to throw up "random" warnings.

Could be that without the trailer hooked up to the 7-pin the electrical load is acceptable. But with the trailer hooked up the electrical load is too much for a borderline 12V battery.

Of course that doesn't explain the hitch weighting issue you described. Unless having weight on the hitch also somehow increases the load on the 12V system in an indirect way.

If you had the vehicle you could test it with ScanMyTesla and look at the 12V power consumption and voltage sag under the various conditions.
 
#5
I suspected the 12V battery as well and suggested that to Tesla roadside service. They apparently were able to see the 12V battery voltage remotely and determined it was not likely the problem. But who knows.

I think I’m encouraged it’s been there for four days now and they are still diagnosing it, they really won’t share anything with me, but I take it to mean they recognize there is some type of issue.

I offered to bring the trailer for diagnostics but they said it was unnecessary and that they couldn’t accommodate it.
 
#8
No loaners due to COVID although I feel like they stopped giving loaners prior to COVID or at least we’re trying to phase it out.

it’s funny you ask because it was a point of a lot of confusion when I dropped the car off Tuesday morning. Roadside service had promised to provide me with an enterprise rental car but local locations were closed on the holiday weekend due to limited hours and COVID. They said I would be able to rent one Tuesday morning. When I showed up to Tesla, they are No contact drop off so there was no one to talk to. I flagged down an employee after 10 minutes and asked him how do I get my enterprise rental car. He said “sorry, we don’t do that anymore, we haven’t done that in a long time. It’s not possible”. I told him what the person on the phone said and he said “hm, no idea why they told you that. We don’t do that anymore”. I said well they made it seem pretty normal, what should I do, how am I suppose to get home, this is my only car”. He said “very sorry, not sure, maybe call roadside service again and ask them. I can give you some Uber credits”.

so, oddly I called emergency roadside service despite not being in an emergency and waited for someone to help me and explained to her and she sighed and said “very sorry, this is so stupid. We don’t know why they always claim this. I’ll help you out.” And she arranged an enterprise rental car for me.
 
#9
Brave Ulysses said:
No loaners due to COVID although I feel like they stopped giving loaners prior to COVID or at least we’re trying to phase it out.
Click to expand...

I doubt loaners will be back until Covid is no longer ANY threat. I doubt that will be anytime this year or next. I don’t think I would want one anyway. Rental car companies are mostly closed, as are Uber and Lyft. So if you have to actually visit a Service Center, better plan on taking somebody along with you to get home. They are all no contact drop off and pickup. At least they still offer Mobile Service :)
 
#10
Some local rental car locations are closed, but that is reportedly due more so for an anticipated drop in rental demand. All airport rental locations and major off-airport locations are still open and actually those locations are busier than ever as a lot of people are opting to rent cars and do long roadtrips instead of flying. Uber and Lyft both seem to be operating as normal, but likely with less drivers as drivers decide whether they want to take the risk or not.

It's a tough situation as this is our only car. So, now as it's in service for its 2nd week, we are very grateful to have a rental car from Tesla through Enterprise even if it was a bit of a time consuming hassle to get it. Even with Uber as an option, it's not a great option when you have a 2 year old with a car seat and need to take her to/from daycare every day. May seem like a corner case situation, but I dont think its that rare. I don't usually swing the entitlement hammer, but there is an aspect of this that the level of customer service and accommodation should maintain some decently high level for a car of this value. I think Tesla overall does a good job, but sometimes they do seem a bit out of touch with inconvenience.
 
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#13
I have the same problem so following this and have a theory. As part of the 7 pin connector there is one spot for a 12v line that is to help power the trailer when plugged in. Recent model Xs have come with that pin disabled, so that the trailer does not draw any power from the car. There is a thread on this, and I don't remember when the change was made to disable that pin, it may be after your build date so yours may be active. I made the manual change to activate mine (easy switch of wires) as I have a wireless brake controller and it needs power. I now notice that about 50% of the time when I plug in the trailer and turn the car on, I get the "power reduced" message. My theory is that when the trailer senses the power and does the initial draw, it's ticking the Tesla computer into thinking there is not enough power for the vehicle. This is probably why they disabled that 12v line in the first place. I've only towed 4-5 times so far and by unplugging and trailer and trying again I manage to get it without the error and driving/towing is normal (and great!).

Hopefully they can figure this out for both of us!
 
#14
Interesting. Kind of relieved to hear someone else is experiencing similar issues. My experience has also been sporadic like yours. Tesla said that they think my trailer 12V system is "back feeding" the Tesla. And this is causing the error messages. I picked the car up today and they are sending a mobile technician to my house tomorrow morning to troubleshoot the car with the trailer. I have to say, it's taken a bit of effort and longer than I had hoped, but Tesla has definitely done everything they can to troubleshoot this issue and I really appreciate them sending a mobile tech so quickly to troubleshoot with the trailer.
 
#15
Brave Ulysses said:
Interesting. Kind of relieved to hear someone else is experiencing similar issues. My experience has also been sporadic like yours. Tesla said that they think my trailer 12V system is "back feeding" the Tesla. And this is causing the error messages. I picked the car up today and they are sending a mobile technician to my house tomorrow morning to troubleshoot the car with the trailer. I have to say, it's taken a bit of effort and longer than I had hoped, but Tesla has definitely done everything they can to troubleshoot this issue and I really appreciate them sending a mobile tech so quickly to troubleshoot with the trailer.
Click to expand...

Good to hear they are working on it - keep me posted!
 
#16
So, a really great mobile technician just spent the last 2.5 hours with me troubleshooting and testing the trailer and the car in my garage.

I've learned a lot, but unfortunately I'm still not an electrical engineer so understand things just enough to be dangerous.

I had the Tesla Littleton Service Center connect the 12V charging pin to power in February (like you said you did yourself) after seeing that thread on here. I actually had to share the link to that thread for them to do the change in February and they still reference that thread. But, according to this technician, he is unsure if the procedure in that thread really is advisable.

After doing a lot of testing, we determined that if you make that 12V pin live in the way that thread recommends, not only do you bypass the trailer harness wiring to get a higher Voltage/amperage from the car's HV system, but you also open the car's HV system up to any current/voltage coming from the trailer. In the technician's opinion, this is a significant risk, and should not be done. The car's electrical system is not designed for this, and he suspects that is why in March 2018, Tesla stopped connecting that wire. But, they have still never made an official note on why they made the change.

His theory is that when the car is not on.... that the trailer voltage of 12.0-12.9V (depending on its state of charge) is confusing the car into thinking there is power and tripping e-fuses which were added to the X at some point (possibly in March 2018). When the car actually turns on, it provides 13.76V (which is actually kind of low, but because the X doesnt have an alternator, it may be the best you can get, especially with the low gauge wire they use). BUT... if the trailer was plugged in prior to the car turning on, it's likely that the car will present those error messages as it thinks there is a power isolation issue... which is a VERY big deal for Tesla and basically leads to the car shutting down. On the other hand.... if you leave the trailer unplugged, turn the car on, and then plug the trailer on.... it most likely wont trip those e-fuses and will work seemingly fine and most likely without error messages. But, this doesn't seem very ideal in practice.

I think he is on to something. Ultimately, what we ended up doing was just reverting it back to the previous wiring configuration. The car seems to put out 12.92V now, but that's not enough to charge the trailer but I'm ok with that considering what the alternative seems to be. The 12V charging pin appears to be "hot" but it's only 12.92V.... not enough to charge anything. but, he thinks that is the way Tesla intends it to be right now as the alternative of moving that wire in that thread poses significant risk to the HV system of the car.

My trailer does not have electric brakes though, so our concern is will I have an issue if I try to tow a trailer with electric brakes, now that the 12V pin is back to its original March 2018 configuration and only putting out 12.92V.
 
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#19
Brave Ulysses said:
His theory is that when the car is not on.... that the trailer voltage of 12.0-12.9V (depending on its state of charge) is confusing the car into thinking there is power and tripping e-fuses which were added to the X at some point (possibly in March 2018).
Click to expand...

Another question is why is your trailer causing such a voltage drop when hooked into the MX 12v system? I've looked at the voltage in the 12V system when connecting my trailer under various situations: when the trailer battery is "empty" (12v), when the trailer is drawing 5V+ from the MX. In neither case does the 12V system in the MX drop voltage (based on CANBUS data of the 12V systems). It's 13.9V. The DC/DC converter power barely changes.

So I'm wondering is there a wiring problem in the trailer causing the initial voltage drop? Or is there some surge load when connecting the trailer? Is the trailer battery fully charged when this is occurring or only when the battery is nearly discharged? Is there a diode in the trailer wiring causing a voltage drop?

If you have CANBUS logging you could look at the 12V system. Or measure the current in the 12V Aux of the 7-pin connector.
 
#20
Sorry, I think that part of my post was confusing. The trailer is not causing a voltage drop.... the 12.0-12.9V range was included just to cover the typical range of my trailer battery depending on its state of charge. At the time of our testing my trailer battery was at 12.75V.

In our testing, the trailer did not drop the Model X voltage. with the 12V hot wired on the Tesla we measured 13.76V. This was reflected in the trailer and would charge the trailer battery, but, it also caused error messages on the Tesla (we believe for the reasons discussed above). Wiring the Tesla trailer plug to match the way it now arrives from the Factory, the 12V pin is still "hot" when the car is in drive.... but it's using the accessory 12 volt power supply from the tow package wiring and putting out just 12.96V (I assume due to the low gauge wiring used for that). In the mobile technician's opinion, he thinks this is how Tesla wants it to be configured and that modifying the Tesla 7 pin plug to move that red wire is problematic and a risk to the car's HV system.


Again... im no expert so I'm parroting information, but that's how he explained it to me.
 
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