Engine Code P1780 Solution!

So had this weird engine code pop up on my truck. P1780.
Did some searching and came up with the problem of "trans neutral Switch".
Replaced the part(100 bucks shipped of rock auto), light went away for about 30 minutes.
Comes back on, so I think it might be a faulty connection. Some Electric parts cleaner and Di Electric grease doesn't solve the issue.

Today out of random luck I was messing with my tail light wiring, because it was pretty torn up.
Connected the wire that illuminates the brake "light" when you hit the brakes back together and boom engine code gone.

The tail light wiring and Trans Neutral Switch is somehow linked?

But anyways just made this post incase someone scoping google is having similar issues.

 

Thanks for this post ! I checked my tacoma for codes this morning ( CEL bulb is dead ) and P1780 appeared... I had to clean my break light connector maybe 2 weeks ago after removing it and replacing it the connection was bad and all kind of weird shit would happen like my fog lights would come on when braking. Anyway. I got this fixed and this is probally what triggered my p1780 ! now its cleared , ill wait a couple of days and check it again and will update this post !

all this to say : thank you very much !

 

Howdy guys, I know this is kind of old, but I am having similar issues, my rear lights have lost their mind and do all kinds of weird stuff like the blinkers and brake dont work on the passenger side but if you turn on the emergency blinker the reverse light blinks on that same passenger side and if you press the brake with the blinker on the running lights light up and not the brake etc

Also my front right headlight is always on when the truck is "on" and when started - so basically whenever the key has been turned, my drivers left head light is usually on when the truck is "on" but not when started... I also have had the p1780 code

what exactly did you clean to resolve your issue? the plug that connects to the tail light housing?

 

I know this is an old post but I just wanted to say a big thanks to the OP @CayucosTacoma for posting this. You saved me a lot of trouble.

So, I want to install a backup camera and was checking out my tail light wiring around where u haul had spliced in my trailer lights connector many years ago. It was getting dark and my flashlight was going dim so I taped it back up and called it a night. The next day I start the truck to drive to work and my CEL comes on and the trans is stuck in low. I can't go over 25 mph! I limp to work (luckily, its only 3 miles away on surface streets) and notice my backup lights are always on, no matter what position the AT selector is on!

I tell my boss I gotta take the day off and limp back home to figure it out. A scan brings up P1780 "Trans Neutral Switch". A quick search takes me to this post and upon closer inspection of my tail light wiring I realize how bad some of the wires are. For example, someone had done repeated crimp type splice attempts in the same area of one wire. My untaping of the wiring bundle the night before had just pushed that damaged wire over the edge. I repaired the wire, cleared the code, and Boom - Problem Solved! OK, I knew it was something I had messed with recently, so that was a big clue, but if you didn't have that would you think a transmission switch problem might be related to damaged tail light wiring? Thanks again OP!

 

Hey, glad to hear that you got your issue worked out.
Definitely unsure how the two are related but is what it is.

 

Glad I found this post via a Google search (over a decade later). Frayed wire is all it was. Now shifts through gears (was stuck in 1st) and CEL is again off. Thanks!!

 

Lol shit what a blast from the past.
Glad it helped you!