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Phil Seastrand
Member
I just got back from the service center on this issue. They found a blown fuse.
Concern: Customer states: The trailer mode indicator is defaulting to blue, indicating a trailer is detected even without the
hitch installed. I can manually override to enable Autopilot but looking for a permanent fix.
Found fuse F105 blown in frunk fuse box. Replaced fuse and tested system. Vehicle now operating as designed. Advise
customer to test trailer lighting system prior to plugging into vehicle to avoid blowing fuse again. Fuse it a Blue 15 amp
micro.
hitch installed. I can manually override to enable Autopilot but looking for a permanent fix.
Found fuse F105 blown in frunk fuse box. Replaced fuse and tested system. Vehicle now operating as designed. Advise
customer to test trailer lighting system prior to plugging into vehicle to avoid blowing fuse again. Fuse it a Blue 15 amp
micro.
Did anyone ever get to the bottom of this? I have the same problem after plugging a non-led trailer with light board into my 2019 model x.
I am trying to diagnose the problem myself as I am interested in maintenance now the car is out of warranty.
What I’ve done so far-
When I unplug one of the plugs on the rear control unit module, the trailer icon disappears, but then ‘schedule service’ appears on the dash.
I ordered a pre-used rear ecu from eBay, but I needed to enter service mode to code it to the car, I did this and reinstalled the software- the trailer icon was still there after. (I’m not sure how to tell if the replacement module even works though) - it was just something to try.
I’ve looked at the wiring diagrams and components locations on teslas website, I’ve checked F105 in the frunk, and that’s ok….
I’ve videos of the processes I’ve tried, so I’m hoping to compose one video when it’s fixed for others to follow…
I’ve requested a price from tesla for the rear ecu and it was less than £200 new. So I’m thinking my next step would be to try that, but I’m unsure if it will solve it now that I’ve tried the 2nd hand replacement…..
Any ideas on fuse locations/relays/things to check?
Currently there is zero volts coming out of the trailer plug next to the tow bar, there is nothing plugged in to the trailer bar plug, and the car still thinks there is a trailer light bar connected as the orange trailer dash light is on. Each morning the trailer icon has turned to blue, and I need to manually disengage it to amber to get autopilot to work.
Any help appreciated, I’ll keep updating here as and when the story unfolds
I am trying to diagnose the problem myself as I am interested in maintenance now the car is out of warranty.
What I’ve done so far-
When I unplug one of the plugs on the rear control unit module, the trailer icon disappears, but then ‘schedule service’ appears on the dash.
I ordered a pre-used rear ecu from eBay, but I needed to enter service mode to code it to the car, I did this and reinstalled the software- the trailer icon was still there after. (I’m not sure how to tell if the replacement module even works though) - it was just something to try.
I’ve looked at the wiring diagrams and components locations on teslas website, I’ve checked F105 in the frunk, and that’s ok….
I’ve videos of the processes I’ve tried, so I’m hoping to compose one video when it’s fixed for others to follow…
I’ve requested a price from tesla for the rear ecu and it was less than £200 new. So I’m thinking my next step would be to try that, but I’m unsure if it will solve it now that I’ve tried the 2nd hand replacement…..
Any ideas on fuse locations/relays/things to check?
Currently there is zero volts coming out of the trailer plug next to the tow bar, there is nothing plugged in to the trailer bar plug, and the car still thinks there is a trailer light bar connected as the orange trailer dash light is on. Each morning the trailer icon has turned to blue, and I need to manually disengage it to amber to get autopilot to work.
Any help appreciated, I’ll keep updating here as and when the story unfolds
FIXED- I’ve now fixed this issue. I booked in with tesla service, but called into the service center before my appointment, one of the techs mentioned I could check what is coming out of the rear control module… tesla did a remote diagnosis and they also thought the rear ECU was faulty, but as I’d already swapped the rear ECU, I didn’t want to just keep guessing (especially at my expense now the warranty is out)….
So, I went into the tesla service portal…
Downloaded and printed the connector and wiring diagrams for my model (all free to anyone)….. I could see that connector X078 left the rear ECU and went straight to the trailer plug X275 under the back bumper next to the tow bar….
I disconnected X078 only, the trailer icon went out…. tested all the pins for continuity, they were all fine…. I gave the loom a pull everywhere I could access it (just to check for pressure faults), then plugged it back in and hey-presto the icon stayed out!
I’m not sure if I released any pressure/wiring faults when I was tugging the loom, or if just unplugging X078, and leaving X073 plugged in made the difference, but the fault has 100% now gone, and I don’t need to take the car in for service….
I’ve plugged a trailer in and the blue dash light automatically comes on as it should, and also fully goes out (not turns amber) when I unplug the trailer
I think it was either the trailers earth fault that caused the wires between the rear ECU and tow plug to fault, and that I freed the fault by pulling the loom and clearing the fault, or that you just need to plug x073 to the rear ECU in and wait for it to boot up before plugging x078 to the trailer plug in…..
I’ll update the YouTube video and also post some pics on here, but I am so pleased it’s sorted…. Total cost was £110 for a rear ECU, a load of time, and many swear words lol
So, I went into the tesla service portal…
Downloaded and printed the connector and wiring diagrams for my model (all free to anyone)….. I could see that connector X078 left the rear ECU and went straight to the trailer plug X275 under the back bumper next to the tow bar….
I disconnected X078 only, the trailer icon went out…. tested all the pins for continuity, they were all fine…. I gave the loom a pull everywhere I could access it (just to check for pressure faults), then plugged it back in and hey-presto the icon stayed out!
I’m not sure if I released any pressure/wiring faults when I was tugging the loom, or if just unplugging X078, and leaving X073 plugged in made the difference, but the fault has 100% now gone, and I don’t need to take the car in for service….
I’ve plugged a trailer in and the blue dash light automatically comes on as it should, and also fully goes out (not turns amber) when I unplug the trailer
I think it was either the trailers earth fault that caused the wires between the rear ECU and tow plug to fault, and that I freed the fault by pulling the loom and clearing the fault, or that you just need to plug x073 to the rear ECU in and wait for it to boot up before plugging x078 to the trailer plug in…..
I’ll update the YouTube video and also post some pics on here, but I am so pleased it’s sorted…. Total cost was £110 for a rear ECU, a load of time, and many swear words lol
Wiring diagrams and connector reference free to download from tesla (in case you didn’t know)
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