Error code P1780?

Tiny
MUSTK
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  • 2001 LEXUS RX 300
  • 3.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
My previous question was removed. However, there is huge update - suspect ECU failure. Vehicle start and running. Replaced NSW and error still active/same. All signals from NSW to ECU seems correct with solid battery voltage, no shorts between wires. I've replaced burnt bulb for "D" on dash and found - when change from "N" to "D", it takes about 3 seconds to "D" appears, same for "2" to "D". When change from "D" to "N" or "2", "D" stay on for 3-4 seconds, together with "N" or "2", then turns off. I open ECU and check for leaked capacitors and cracked soldering points - all seems OK, cleanup ground to cover. Check, and now time to change indicator changes to 5-10 seconds. It is feels as capacitor slowly charge and slowly discharge. There is JC8 on the way to dash from ECU that I plan to check, but very low chance it would be root. Also, I want to check if there is any delay from NSW to ECU - low chance since there is simple mechanical switch, so disconnect should be quick. Have no idea where to look anymore. Can you please advise what to check. Thank you.
Sunday, March 17th, 2024 AT 9:55 PM

32 Replies

Tiny
KEN L
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When the P1780 code is set, it means the vehicle's control module has detected a malfunction within the park/neutral position switch circuit. I would try disconnecting the ABS controller to see if the action to the inductor lights gets any better. This is where the JC8 connector breaks off to the ABS system. Also did you do a CAN scan? It might be the instrument cluster itself that is bad. You can get a CAN scanner (Controller Area Network) which will work on most cars from Amazon.

Here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

Here are the wiring diagrams for the neutral safety switch so you can see how the system works. I don't think it can be the PCM. Here is how to change out the cluster which you can send out for testing. Check out the images (below). Please upload pictures or videos in your response to the problem so we can see what's going on.
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Monday, March 18th, 2024 AT 12:21 PM
Tiny
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Hi Ken,

Thank you for quick response.
I use CAN scanner - Autel MD808P.
By disconnecting ABS controller you mean skid ECU, ABS pump, or JC8 connector?
Do you have a picture how JC8 is looking, or I can try to trace it from ECU.
And you might be right about ABS, not so long time ago it was lit: check, VSC and ABS, after reset all were gone for some time and then get back only with check and VSC. We replaced VSC module, and got same results, then I found online that VSC error is always appearss when check appears.
Visually, all boards on ECU, and cluster seems okay.
BTW your wiring diagrams way better than I found online, easier to work with.

Unfortunately, it is my dad's vehicle, and I am able to work on it once per week.

Thank you again for your help!
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Monday, March 18th, 2024 AT 1:03 PM
Tiny
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If I will not find JC8 connector, I guess, I can remove pin/wire 22 from connector A23.
It should work to test, correct?
Thank you!
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Monday, March 18th, 2024 AT 7:40 PM
Tiny
KEN L
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Yes, I mean the ABS controller (skid ECU) the connector they don't show where that is. I would double check the wiring between the gear range sensor and the PCM. Also you may have a defective sensor or the wiring connector is not pushed down all the way, can you check that as well?
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Tuesday, March 19th, 2024 AT 8:59 AM
Tiny
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Good morning, Ken,

Thank you, we already checked several times new and old sensors, both working, and reconnect connector and make sure it is secure.
Also, it seems I might locate, in theory, JC8. Found how it should look by part number, then search for dash wirings on sale.
I've attached pics.
I will proceed with advised steps on the weekend and report.
Thank you very much for your help, now I have an idea where to look.
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Tuesday, March 19th, 2024 AT 9:28 AM
Tiny
KEN L
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Once you go over the wiring which sounds like it is the problem but if not the PCM will be next, just to confirm you have power at the blk/wht wire at the gear range sensor with the ignition key in the "crank" position, correct?
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Thursday, March 21st, 2024 AT 11:17 AM
Tiny
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Hello Ken,
Everything before ECU seems okay. Found JC8 connector, it sits on same bracket where ECU, looks different than found by part #. Found tester to measure capacity, seems 3 dead and one degraded capacitors. Please see attached pics. Will order capacitors and re-solder when arrived. Will post updates once proceed.
Thank you for your help!
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Sunday, March 24th, 2024 AT 2:13 PM
Tiny
KEN L
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Can I ask if you had power at the blk/wht wire at the gear range sensor? It looks like you got it under control let me know what happens.
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Sunday, March 24th, 2024 AT 2:33 PM
Tiny
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Thank you.
On battery 11.5v now, On switch black/white -10.5v. On ECU and ABS - "D" 10.5v
Now I'm really suspect ECU capacitors, especially with measurements.
I'll keep you updated.
Thank you!
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Sunday, March 24th, 2024 AT 4:12 PM
Tiny
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Hello Ken,
Today I received and replace capacitors.
Offboard 2x 10uF caps show 0. Others out of range, however might still work with reduced performance.
Next weekend I'll test on vehicle and report.
Thank you again for your help!
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Sunday, March 31st, 2024 AT 8:21 PM
Tiny
KEN L
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That seems like low battery voltage, has the battery been tested? The black/white comes straight from the fuse panel so it should be 12 or over.
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Monday, April 1st, 2024 AT 7:20 PM
Tiny
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Battery is okay, it discharged while checking everything. Usually, when not running, it is over 12v. Will see next weekend.
Thank you!
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Monday, April 1st, 2024 AT 8:24 PM
Tiny
KEN L
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Sounds good, let me know what happens.
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Tuesday, April 2nd, 2024 AT 8:24 AM
Tiny
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Same thing. Only D it's on faster sometimes. Maybe something on the speedometer part. When run live data on scanner it shows all changes right away.
Thank you!
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Saturday, April 6th, 2024 AT 9:40 AM
Tiny
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Not speedometer. I completely removed it. Reset error and check. After changing lever, error get back.
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Saturday, April 6th, 2024 AT 10:21 AM
Tiny
KEN L
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I see your other question in the que it has not been approved, did you get an email for it to be approved? Because the scanner sees what gear you are in, but the cluster does not, I would send the cluster in for testing or try a used cluster to see if that fixed the problem. You might be able to take the cluster apart and see if anything is burnt. Check out the images (below). Please let us know what happens.
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Saturday, April 6th, 2024 AT 11:23 AM
Tiny
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It was approved, and then gone, I just created another question/thread. It is okay. Thank you.

I took a cluster apart and did not find anything suspicious. I also completely unplugged it, reset error, shift lever several times, waiting 20 seconds on each position, and got same error. Do you think 1V difference between battery and NSW might cause it?
I took ECU with me, so I will check again.

Thank you!
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Saturday, April 6th, 2024 AT 10:34 PM
Tiny
KEN L
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I don't think 1 volt will matter, I would try a rebuilt, used cluster. I would say try a gear range sensor but the scanner seems to be able to see it working correctly.
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Sunday, April 7th, 2024 AT 10:15 AM
Tiny
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Thank you! I will get used cluster on eBay, hopefully will receive before next weekend to try. Will report once get any input.
Thank you!
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Sunday, April 7th, 2024 AT 12:01 PM
Tiny
KEN L
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You are welcome, let me know :)
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Monday, April 8th, 2024 AT 10:14 AM

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