Mystery of The High Beam Shifter

Searching for Clues!

I have a 2000 4Runner 3.4L SR5 (automatic transmission), with a bunch of electrical gremlins. I suspect most are due to the buffoonery of the kid that owned it before I did. One particular gremlin that I must exorcise is complete a mystery to everyone I have consulted. The issue is as such: When driving with the lights on, all is well on low beams. However, the very instant you turn on the high beams, the vehicle instantly shifts into first gear on its own regardless of, well, anything, to include the speed and gear you may be in at the moment. Quite the event at 65mph! Once the high beams are on and the instantaneous shift into 1st gear has occurred, there is no more shifting. It is locked into first gear until you return to low beams. Then, with a slight hesitation, you're back to normal operation. There is nothing that you can do to stop or mitigate this and so for 7 years I have not used my high beams.

This issue is as terrifying as it is infuriating. I find myself staring at my 4Runner and talking to myself like a mad man wondering why and how such a thing could happen. What possible mechanism or routing of electrical current could cause such a thing? I've traced the wiring and there is nothing shorted, spliced, added onto, etc. I've replaced every fuse and relay in the entire vehicle. I've measured the current in high and low beams and it's normal. What in hell could cause this? The lights should have nothing to do with the transmission in a sane and rational world. I think...?

Has anyone else experienced this? And if so, has anyone fixed it and how?

 

No clue man that is definitely a strange one. I’m guessing you have traced the wires in the high beam circuit?

 

Oh yeah, many times. I actually might be onto something from another forum. Looks like some other folks have had the same issue and it has to do with a cracked display circuit board. I'll post here when I replace it and we'll see if it works!

 

I think the headlights and transmission may share a ground somewhere. I've heard of this before.

 

I believe it's on the left side under the dash. I would try separate grounds and see if that helps.

 

Many thanks! I'll try try to find that and try it. Sure would beat replacing the circuit board.

 

I ran it by my mechanic buddy who is the one who has seen it. He said a customer had a windshield replaced that had been leaking on the A pillar somewhere. Dripping down onto the ground causing corrosion and a short

 

From an engineering standpoint, it seems you'd do everything possible to avoid even the slightest possibility of this ever happening.

 

Many thanks! Definitely something I had not looked at yet. I'm on it!

 

You would think so, wouldn't you? I LOVE Toyota but sometimes I find things that really make me shake my head.

 

Good luck

 

You need a wiring diagram and a volt/ohm meter. Find what parts the high beams and the TCM share (realistically instrument cluster or a ground) and start checking there. Resistance tests are a waste of time, you want to start checking voltage drops. Your most likely going to find a voltage drop on a shared ground between them which in turn would back feed voltage to the trans. If they truly share nothing then there is damaged wiring insulation, rodent chew maybe, that is allowing the copper strands to touch between them.

With multiple electrical gremlins it’s good idea to start with disconnecting and cleaning the battery cable connections then voltage dropping every ground you can find with the vehicle turned on running with as many electrical loads running as possible (lights, radio, defrost, a/c, heated seats, wipers, something charging in the power outlets, etc.)

 

I have the same issue with a 99 limited. I have noticed that when I pull on the high beams the gear selector lights in the dash go crazy so I'm planning on digging Into the cluster. Also I have noticed if you use the button in the dash to change shift points (like a tow/haul) button has the same reaction as switching to high beams

 

NORCO did you ever find out what it was? I bought a runner that's having the same issue.

 

Morning, you never shared what the final result was, what the problem was and how you corrected it. I’m having thesame exact issue with my 2000 Toyota four runner as well. Thanks.