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Trailer hitch wiring harness causing error messages?

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#21 ·
stevenericmost said:
Yes, that seems to be the cause as that is exactly what happened to me. My son is an electrical engineer and he suggested the harness may have a diode in the control module that conflicts with LED lighting.
The question for me now is, should I seek to recover the $400-plus that it cost me for the harness, installation, and removal by the shop I went with? A painful lesson for them, but in the end they are responsible for installing an incompatible product on a customer's vehicle.
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I have the Tekonsha harness, have even wired in trailer brakes- no issues. The brake controller side took some very careful planning and specific parts to NOT throw errors.

If you want to be 100% compatible, go with the OEM harness PK5D0-42K11-WH - Towing Wire Harness - 2019-2023 Toyota | OEM Parts To You You shouldn't need to mount the connector outside, route it to the wheel well and plug it into an extension hanging out of the hatch when you need it.
 
Discussion starter · #22 ·
chuckles70 said:
I have the Tekonsha harness, have even wired in trailer brakes- no issues. The brake controller side took some very careful planning and specific parts to NOT throw errors.

If you want to be 100% compatible, go with the OEM harness PK5D0-42K11-WH - Towing Wire Harness - 2019-2023 Toyota | OEM Parts To You You shouldn't need to mount the connector outside, route it to the wheel well and plug it into an extension hanging out of the hatch when you need it.
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Thanks so much. Do you know if there's a youtube video of the installation, or are there good instructions in the package?
 
#23 ·
stevenericmost said:
Thanks so much. Do you know if there's a youtube video of the installation, or are there good instructions in the package?
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Instructions attached. I'd say this is DIY friendly with a small amount of courage. If you've ever used a socket wrench it's doable. It's not necessary to take the seatbacks etc. out like the instructions say. They want you to pull the whole rear side panels, but you can leave the seats in and have plenty of room by just popping the back half of the side panels and pulling them out a little.

But you have to pull most of the plastics in the rear to get to stuff. That's screwdrivers for some nuts, sockets to pull the tie down harnesses, pop a few of those panel clips, etc. And remembering where everything goes that you took out.

I'm sure there are YT videos out there...
 

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#24 ·
I did Tekonsha too. Would actually be a worthy first project for a new DIYer. Not easy, but there are lots of youtube vids and fundamentally nothing super dangerous or tricky. You might own a new tool or two at the end (I'm thinking a crimp tool for the wiring lug might not be in everyones basic tool set, and a wire stripper too).

One thing I noted about the Tekonsha, the controller unit needs to be mounted somewhere. DON'T apply the double sided tape and try to mount it too soon. Wait to the end. Because you get the location wrong and then not have enough slack right to left to route all the wires as you put things back together. This was the one thing that the video glossed over. Prolly cause they guessed right when mounting the controller. Well I guessed wrong. Simple fix -- relocate the controller. But annoying enough to remember.
 
#25 ·
FYI
Update to my original post on the Curt wiring harness throwing codes. Talked to some independent installers and they all said it should work fine. One mentioned that if you have a poor ground with led lighting it will drive the car computer crazy. Re-installed everything and made sure I had a good ground. I originally relied on a star washer to cut through the epoxy primer and anchored it with a bolt into an existing threaded hole. This time I used a tap to clean the threads, sanded the ground area to metal and used another star washer. Tested with a multimeter to ensure a good ground and now the trailer wiring system works fine. FYI
 
#26 ·
89-300ce said:
. One mentioned that if you have a poor ground with led lighting it will drive the car computer crazy. Re-installed everything and made sure I had a good ground. I originally relied on a star washer to cut through the epoxy primer and anchored it with a bolt into an existing threaded hole. This time I used a tap to clean the threads, sanded the ground area to metal and used another star washer.
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The Toyota OEM trailer wire harness instructions have you use the bottom mounting bolt for the Fuel ECU bracket for the ground. That mounting bracket is bare metal; the Toyota instructions make no mention of having to clean that area for a good ground, so I assume that bracket/bolt is a good place for the ground.
 
#32 ·
cdherman said:
Disagree. But not vehemently. I would remove the aftermarket stuff. Entirely. If the errors stop, the fine, you have your culprit. But stealerships are famous for blaming all sorts of anything installed by anyone except themselves (and even them sometimes) for whatever is wrong with your vehicle. You will NEVER get the dealer to actually figure out the problem, so long as the aftermarket stuff is in there.

And then, since your vehicle is in their system, even if the problem persists, they will say you/your installer damaged something . Might need to remove and then find a different dealer and hope they don't share information.

I used a Tekonsha harness. Should ANTHING electronic happen to my RAV4, I will likely remove the wiring entirely before taking to a dealer. Dealers are just generally lazy SOB. Honestly, even with an OEM wiring harness, I'd expect a dealer to blame a different dealer if it was installed elsewhere.
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You are so right about the dealer blaming a problem on aftermarket stuff even if they installed it. I had tow hitch, seven pin wiring and brake controller installed before purchase. A 2023 TRD off-road purchased brand new. They have now removed the wiring harness and brake controller saying that is why the door handle and key fob lock/unlock is not working properly. It is an intermittent problem, mostly when it is raining. Has anyone had trouble after installing tow package
 
#34 ·
M1dtom said:
Installed curt hitch and harness last yr, never tested it, got it for my boat but never used.
So yesterday I backed up and. Plugged it in , worked fine.
Do you have to be moving to get errors?
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No. Gives errors anytime the ground connection is bad.
 
#35 · (Edited)
FKHeath said:
You have a Prime, so the 12 volt battery is in the back where the power for the trailer wire controller is connected. All OEM (and most after market) wiring is done in the back. No need to run wires to the front or the dash. The OEM trailer wire harness installation takes, at most a couple hours, not $1800. It is not a big job. (See the instruction PDF file for the installation instructions.) The OEM wire harness installs the same way most after market harness do.

Be sure you keep the front radar sensor (Toyota emblem) clean. When in a snow storm, my radar cruise control would shut down when that sensor got slush on it. Like wise the windshield where the photo sensor is located, up by the rear view mirror.
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my apologies if I missed the comment or thread where the PDF install document is posted. What are you referring to by “See the instruction PDF file for the installation instructions.”?
 
#36 ·
Snobud said:
my apologies if I missed the comment or thread where the PDF install document is posted. What are you referring to by “See the instruction PDF file for the installation instructions.”?
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See post #23 above.
 
#37 ·
89-300ce said:
FYI
Update to my original post on the Curt wiring harness throwing codes. Talked to some independent installers and they all said it should work fine. One mentioned that if you have a poor ground with led lighting it will drive the car computer crazy. Re-installed everything and made sure I had a good ground. I originally relied on a star washer to cut through the epoxy primer and anchored it with a bolt into an existing threaded hole. This time I used a tap to clean the threads, sanded the ground area to metal and used another star washer. Tested with a multimeter to ensure a good ground and now the trailer wiring system works fine. FYI
Click to expand...
a bit of grease on the ground connection helps as well to hold down rust or corrosion for future.
i like red grease for battery or for any grounds that might get moisture.
or you can use silicone grease
 
#38 ·
FKHeath said:
See post #23 above.
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I am so sorry I missed that post 🙈. Thank you soooo much ❤🎉 for pointing me in the right direction. I had the hitch being installed today and the installer called me and there was a bit of an issue. Now I can go back and check the install and make sure everything is wired up correctly And if not I have this now. Thank you sooooo much!
 
Discussion starter · #39 ·
Here's an update on my wiring harness saga.
To review, after having a harness of unknown brand installed by Street Scene in Watsonville, CA I drove perhaps a thousand miles without incident during our major winter dump out here in California. At some point I started getting error messages about reduced braking ability and the cruise control and lane keeping became disabled.
I took the RAV4 Prime into the Capitola Toyota dealership where after a couple unsuccessful visits they diagnosed the problem as the harness. They told me only the dealer installed harness would work properly.
At that point I took the car back to Street Scene and told them to take off the harness. They charged me $175 to do that and after the removal said the ground wire was not making good contact. At the time I didn't think much of the comment and was glad to have all electronic systems back to normal.
After reading some posts on this forum about possible grounding issues with harnesses I decided to have my electrical engineer son, Matthew, attempt to reinstall the same harness. We attached the ground wire directly to the 12 volt battery in the hatch area of the vehicle.
I have since driven thousands of miles, including a little U-haul trailer pulling, and have had no problems.
So apparently Street Scene improperly grounded the unit during their installation. I plan to go back to them and demand a refund for the removal because they improperly installed the harness. Small claims court may be in my future.
 
#40 ·
stevenericmost said:
Last June I had a trailer hitch wiring harness put on my 2021 RAV4 Prime by a company that does this sort of thing routinely. There were no issues with the car up until this February when I started getting messages on the instrument panel saying things like "Pre-Collision System Malfunction Visit Your Dealer" and Cruise Control Malfunction Visit Your Dealer and LTA Unavailable.
I took it into the dealer and after several failed attempts to come up with a diagnosis they finally said it was the aftermarket wiring harness.
Now the harness was on there for 9 months and I had zero issues with anything. I drove thousands of miles and everything worked great. If the wiring harness isn't attached to anything and isn't drawing any current how can it have any affect on anything? It's just a plug capped off under the bumper.
Could the dealer be trying to just get rid of me? Help please.
Click to expand...
You must install a diode in the trailer brake controller harness. Tekonsha sent me a free harness replacement that I wired in, it has the diode included inline. The diode stops feedback loop to the collision sensor that activates the warning error.
 
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