I know this sounds funny, but my 2000 auto trans 4runner won't shift when my brights are on. Let me start from the beginning. On Christmas I hopped into the 4runner and notice it wouldn't shift. It was a cold day (10 deg) so I drove it for 3 miles in the thought that it might warm up and shift. It did not. I got home and scanned it. It threw a p1780 neutral safety switch code. I replaced the switch and it still didn't fix it. Then I took it to ammco. They looked at it and said the transmission was good and it's a " electrical gremlin" and weren't qualified to fix it. Word on the street is that it could be the cluster. Has anyone ever seen this before?

More of what I have noticed:
* if I clear the code and drive it without the headlights on, the code does NOT come back on and drives fine
*drives good most of the time with the headlights on.
*the second you turn the brights on, it drops to first! I turn the lights off and back on, it shifts normal.

Thanks for reading!

 

Now that's truly one of the weirder things I've heard of. Um...

 

Subscribed.

 

That just sounds painful to figure out.

Bad grounds? Back feeding current? Loose connection/low voltage somewhere?

At least you've gotten the first half of the battle completed, figuring out precisely how to trigger the problem.

 

I'm just guessing here.

Do you have a remote starter or alarm?
Anything else aftermarket?

If you unplug the headlights does it still fail if you activate the high beam switch?

 

That's a good question. No I don't. All of the Electrical on the truck is bone stock. That's a good idea to unplug the lights and see what happens. I'll pull some fuses and see it affects anything. Today is the first day I can drive it during daylight hours. It's dark on the way to and from work. Stupid winter.

 

Funny that a supposed High End Trans shop was clueless.

Are you having any charging system faults?

I am not a Auto trans person and have no idea how to drive one!!

Is there a fail safe if voltage drops to low that allows you to get the vehicle off the road.

Just like the ECM I would venture the Trans computer is effected by low voltage.

Interesting problem .

 

Bump :-)

 

Ok, you bumped it, but did you try anything?

 

Drops to first without to having to touch shifter?
When you say it does not shift, do you mean the shifter gets stuck, OR you're able to move the shifter, yet the transmission stays in last gear?

You replaced the neutral safety switch but did you check connections/power/ground TO and FROM the switch are good?