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Codes P1860, P1626, P0785 and P0740?

Tiny
EARL91
  • MEMBER
  • 2000 CHEVROLET TAHOE
  • 5.7L
  • V8
  • TURBO
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
The vehicle listed above is a z71 old model. I just installed a brand-new rebuilt transmission. This is the second one in just a few months. When I clear the DTCs the noise it is making goes away for a few seconds. So, I know the transmission is good. Its giving a p1860, p1626, p0785, p0740. Please help.
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Monday, January 29th, 2024 AT 6:02 AM

25 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,245 POSTS
Can you please shoot a quick video with your phone so I can hear the noise? That way I can tell for sure what's going on. You can upload it here with your response. We need to hear the noise, so we know which direction to go to help you fix the car. It takes time to upload so please be patient.

P1860 - TCC PWM Solenoid Circuit Electrical

P1626 - Theft Deterrent System Fuel Enable Circuit

P0785 - Shift/Timing Solenoid Malfunction

P0740 - Torque Converter Clutch Circuit Malfunction

With these codes I would check the electrical connector at the transmission make sure the connector is free from dirt and that it is in good shape and fully secured. If so then the problem is inside the transmission. I would get a rebuild valve body to install, if you know the transmission is good, I would replace the PCM with rebuilt unit but check the electrical connectors first. You can get a preprogrammed unit by searching Google or Ebay. Check out the images (below). Let us know how it goes.
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Monday, January 29th, 2024 AT 10:40 AM
Tiny
EARL91
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  • 88 POSTS
If I clear the code. The sound goes away for a split second.
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Tuesday, January 30th, 2024 AT 8:10 AM
Tiny
KEN L
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Thanks for the video. If the codes come back that fast it is a hard code. How is the condition of the transmission electrical connector? Also did the vehicle have these codes before you started the repairs?
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Tuesday, January 30th, 2024 AT 10:20 AM
Tiny
EARL91
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The connector condition is good. I cleaned them and checked. Nothing wrong there from what I can see. Yes, the truck did have the codes before the repair. I can't reset the tap with the scan tool. And I'm not sure how I could do a reset to see if that might fix it.
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Tuesday, January 30th, 2024 AT 12:26 PM
Tiny
EARL91
  • MEMBER
  • 88 POSTS
I had just found the wires leading to my distributor or all crushed and busted open. Could this be a leading cause of my issue?
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Wednesday, January 31st, 2024 AT 9:14 AM
Tiny
KEN L
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Yes, this can cause the problem, I would repair the wiring and then clear the codes again to see what happens.
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Thursday, February 1st, 2024 AT 11:31 AM
Tiny
EARL91
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No change.
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Sunday, February 4th, 2024 AT 9:58 AM
Tiny
KEN L
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Okay, I would try the PCM then, let me know please.
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Monday, February 5th, 2024 AT 10:35 AM
Tiny
EARL91
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  • 88 POSTS
I replaced the PCM no change. I have no idea what it could be. I hope they didn't send another transmission with issues.
Still has p1860, p0758, p0753, and p0740.
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Tuesday, March 5th, 2024 AT 12:26 PM
Tiny
EARL91
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Where can I get a new wiring harness?
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Wednesday, March 6th, 2024 AT 7:22 AM
Tiny
KEN L
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I would try a wrecking yard, if the wiring is repaired then I would suspect the transmission is having an issue, did you have these codes before you started with the new transmission?
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Wednesday, March 6th, 2024 AT 8:45 AM
Tiny
EARL91
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Yes, I did. This is the second transmission. First had forward gear engaged all time.
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Thursday, March 7th, 2024 AT 5:32 AM
Tiny
KEN L
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I would try a new wiring harness if this has been the same problem with a different transmission. To be sure you can check the wiring by following this guide. You should be able to repair the wiring.

https://www.2carpros.com/articles/how-to-check-wiring

Here are the complete wiring diagrams so you can do the testing. Also, double check the fuses in the wiring diagrams for power with the key on. Check out the images (below). Let us know what you find.
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Thursday, March 7th, 2024 AT 9:50 AM
Tiny
EARL91
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  • 88 POSTS
So, my gauge cluster does not work. I know in certain vehicles that if the gauge cluster is bad, it will affect the transmission. Do you think this could be the issue?
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Saturday, March 9th, 2024 AT 6:30 AM
Tiny
KEN L
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Yep, I have seen that as well, the cluster is a part of the CAN network.
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Sunday, March 10th, 2024 AT 10:54 AM
Tiny
EARL91
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So, I believe I am starting to narrow things down. Either it's the cluster, ignition switch or a speed sensor or bad connector. Or neutral safety switch. It honestly all that is left.
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Monday, March 11th, 2024 AT 8:38 PM
Tiny
KEN L
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Did you check the wiring?
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Tuesday, March 12th, 2024 AT 11:38 AM
Tiny
EARL91
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I have. I can't seem to find any alarming issues.
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Wednesday, March 13th, 2024 AT 5:38 AM
Tiny
KEN L
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With these codes it will be inside the transmission the wiring or PCM which you say you have checked or replaced.
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Wednesday, March 13th, 2024 AT 9:25 AM
Tiny
EARL91
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New PCM and new transmission.
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Wednesday, March 13th, 2024 AT 9:27 AM

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