Need Help With code P1780 Neutral Safety

I have a 98 4 Runner that is driving me crazy and I am in need of some advice. I'm on my 3rd neutral safety switch and they all throw the same code (P1780 Transmission Park/Neutral Position Fault) with the same symptoms.

Associated symptoms include blowing the 10 AMP fuse for the gauges, power windows, heater-AC blower. I cant remember what else. It will allow you to put the transmission in reverse and sometimes into drive. Even when it allows you to put it in drive it will blow the 10 AMP as soon as you try to move it. The switches are all adjusted correctly from what i can see. I checked for melted wires on the transmission all the way up to the engine where they became difficult to check them more.

I'm at a loss and it is driving me nuts. Not sure what else to check and any help would be greatly appreciated.

 

Trailer lights plug shorting out?

 

I pull a trailer quite often with it and all the lights were functioning properly but I'll definitely check again.

 

I found this on alldata at work. Hope it can help lead in the right direction.

 

Looks like everything goes back to the neutral safety switch. I've seen that before about the ecm too. Some people say it could be a short in a lighting wire. After 2 neutral safety switches and checking other stuff I'm sure frustrated. If I had faith in the Toyota dealership I would take it to them. I definitely need to get it fixed though. The 1st time it blew the fuse I was accelerating up to highway speeds and it blew at around 40 mph. Now it blows in drive with about 1500 rpm. Never in reverse. I know electric issues can be a pain but this thing has me scratching my head. Thank you everyone for the advice so far.

 

I'm still fighting with this if anyone has anymore insight.

 

If it's not the actual switch, it could well be the wiring. You can easily check all the wires going to/from the PN Safety switch. Pull it's plug out, one multimeter lead to a good ground someplace, meter in ohms, low scale, and use the other meter lead to check each pin of the switch's plug. Not the side that goes to the switch, the side that goes to the rest of the truck. With the meter lead in the plug, make sure you, or a helper, wiggles the wire bundle around.
Be aware that a lot of those wires go through a lamp in the gauges, then to ground. Lamps don't have a very high ohm value. Maybe pull the plug that goes to the gauge set as well. You're looking for a short to ground, or a wire-to-wire short. After you've checked them all for shorts to ground, check each pin for a possible short to another pin.
Since a short in a wire to another wire doesn't matter the polarity of the meter leads, you don't need to reverse the leads after checking one of the pins to another. IE: red meter lead to pin 1 in the switches plug, black lead to pin 2. If it checks good, high or infinity ohms, move the black lead to pin 3. Then pin 4, etc. After you've done this with all the pins in the plug, red lead to pin 2, black to pin 3, since you already checked pin 1 to 2. Then move the black lead to pin 4, etc. Then red to pin 3, black to pin 4, etc etc, until you ohmed out ALL the wires.

Make absolutely sure you pull the leads off the battery, and let them sit for a few minutes, before doing your ohm checks. It only takes a very slight amount of voltage to a meter in ohms to trash the meter. You want to make certain that not only the battery is disconnected, but that any capacitors have had time to drain down before you do any ohm readings.

Hope this helps a little...
Pat☺

 

I somewhat checked the pins in the harness quick yesterday while I was messing with it. I found the red/yellow wire in position 8 that is grounding out. Not sure what this wire is as I haven't checked yet. I've always thought it might be a short in the wiring but I hope not because that is a pain to change and expensive. Finding a short would probably be a massive pain as well.

 

From what I can see on the wiring diagram I have, pin 8 is a green wire. BUT: The wiring colors can change at random intervals. I think, personally, if Toyota runs low on a particular color during manufacturing, they just throw in a color wire they have plenty of to take the slack.

Anywho, that wire goes to the gauge set, to light the LL light, and to the engine control module. Bear in mind, as I said, lights don't add a whole lot of resistance to a circuit. You might want to disconnect the plug to the gauges, so you're not reading through a light bulb.

Having said that, if it's possible, start splitting the circuit in smaller sections. IE: If there's a plug about 1/2 way along the wire's route to the gauge set, unplug it. Then check the resistance to ground on each half. One will likely have the reading that's suspect, the other will be good. Then you know which half of the circuit to follow. Reduces the length of wiring you need to trace.

Anywho, you may just need to trace the wire visually, end to end, to find the trouble. Sounds like the wire either rubbed on something until it wore through the insulation, OR the insulation, which is pretty old as far as wire insulation goes, cracked somewhere, allowing the wire to touch something it shouldn't. I would put my money on a rub someplace, but you never know. Just start un-looming the wire, and look for a place it rubbed. A corner, where it goes through a grommet that is old and cracked or broken, something like that.

BTW: A short like that would appear to the computer to be the switch, so that's why it keeps saying the switch is bad. Presuming, of course, the replacement switches you've put it are known to be good, and the switches, once installed, are aligned correctly.

Let us know what you find. And all the fun you have chasing a single wire through all the places it runs
Pat☺

 

I disagree on the wire colors changing for no reason. If TOYOTA changed colors willy nilly, future repairs would be absolute chaos for technicians.

If you aren't using the Factory Service Manual diagrams and the ones for the EXACT year, then you will get oddities along those lines.

The FSM diagrams are really detailed down to every junction. Anything else by like Haynes/Chiltons will try to simplify things.

 

I will continue to dig into it more as time allows. Another thing worth mentioning that I discovered is the gear idicator lights in the instrument cluster all light up except the DRIVE light. I've tried adjusting the N/S switch to activate the light with no success. I will try another switch to verify. I've checked things with the gauge cluster disconnected and removed with the same results as before. I might buy a new printed circuit board for the gauge cluster as they are cheap and easy before I start tearing into the wiring more. Some say this can cause issues but its mostly with multiple lights in the cluster doing weird things. Mine doesn't do anything other than not lighting up the DRIVE light.

 

Hmmm...Sounds like my ex wife.


Sorry, I just couldn't resist. Having said that, if you knew my ex...

Anywho, is it possible the Drive light in the gauge cluster might be burned out, affecting the circuit in an odd way?


As you can see in the diagram above, that bulb burning open, could have detrimental effects on the entire circuit. I don't know if the bulb is available, although I'm pretty sure it is, and I don't know if it's soldered in or in a socket, and whether or not it's worth your time and effort to desolder and resolder it into the gauge cluster circuit board, having to be careful of lifting a run, and so forth. It might be well worth the cost, even if it's not very expensive, to just replace the whole circuit card, as you said.

Have fun, all!
Pat☺

 

I don't think the bulb would affect the circuit if burned out. The "17 E" connection in that diagram goes to ground. Therefore, the D Bulb appears to go to ground via a resister...not sure why it's the only one to do so but it seems like there's not much it can affect.

Regardless, do start with the bulb and see if it's good and check to see why the W-R wire on connection "5 C" isn't getting power from the transmission selector switch which is not shown in the above diagram. W-R should be white/red stripe.

If you are getting 12v on that W-R wire, then the ground or resister on the circuit board is bad. Since it is the only light that has gone out...and the only one with a resister to ground...maybe that resister went bad...unlikely but it would make sense.

 

Bad resistor, or lifted run, or pad.
I've seen a lot of circuit boards that have cold solder joins, or insufficient solder on the pad, cracked runs, etc. As the circuit card flexes, which they do in an automobile, it can cause a cold solder join to eventually crack and no longer make connection the way it's supposed to. It might not even be the resistor's solder joins. It could be the connections to the plugs, to ground, whatever. Mass production errors happen. Often.
Even if the resistor burned, which is pretty obvious to the naked eye, they can be replaced fairly easily, as long as you're a decent solderer. Just make sure the value of the resistor, and it's power rating, are both correct.
If you're going to replace the circuit card entire, then you can take your time, and inspect the old one carefully for any defects it might have. You may just need to re-flow a solder join, bridge a cracked run, whatever, and then you have, essentially, a new circuit card to swap in if you ever need it again.
Spare parts on-hand can save a lot of money, and time. Good things to have.

Keep us posted on how things go for you!
Pat☺

 

Hey ! This is Chuck.I have a 97 4 runner 3.4 automatic. Iam having the same promblem that you was having. My 10 amp gauge fuse blows , so cluster gauges, power windows,blower motor stops working. CEL comes on showing code p1780 change pk neutral switch, still having same problem. Have you figure out what’s wrong with 4 runner? Any help would be appreciate .