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Discussion Starter · #1 ·
Hello all!

I recently started working on my brother in laws 2005 1500 with a 5.3 - 4l60 combo that went into limp mode and lost 1st and 4th gear. It'll shift between 2nd and third manually. The A and B, TCC PWM, and 3-2 solenoid were replaced by a buddy of his because they believed that was causing the issues, none of which resolved the transmission problems. Here is the list of codes that were pulled that made them go down that rabbit hole.

P0740 "TCC solenoid circuit"
P0753 " 1-2 A shift solenoid control valve circuit"
P0758 "3-4 B shift solenoid control valve circuit"
P0785 "2-3 shift solenoid circuit"
P2761 "TCC pressure control solenoid control circuit"

Now that they have given up on trying to find the problem, I now have the truck in my shop. I checked for voltage at pin E on the transmission connector and am getting a little more than 12 volt. I then disconnected the PCM connectors and tested for continuity between the following circuits between the transmission and PCM.

Blue connector

Pin 17 to pin R (Transmission pressure switch B). Good
Pin 18 to pin P (Transmission pressure switch C). Good
Pin 75 to pin E (Ignition 0). Good
Pin 79 to pin S (3-2 shift solenoid valve control). Good

Green connector

Pin 2 to pin U (TCC PMW control valve). No continuity
Pin 6 to pin C (PC solenoid valve control high). No continuity
Pin 8 to pin D (PC solenoid valve control low). No continuity
Pin 42 to pin T (TCC solenoid valve control). Good
Pin 63 to pin N (Transmission pressure switch A). Good

I haven't had the chance to test the following pins on the green PCM connector.

Pin 47 to pin B (2-3 shift solenoid).
Pin 48 to pin A (1-2 shift solenoid).
Pin 51 to Pin L (TFT sensor signal).

While I'm leaning on the transmissions internal harness being bad, I can't say for sure due to the few circuits that didn't have continuity. That may be due to the fact that I used pinout diagrams that I found online and can't verify that they are 100% accurate or correct for this year model.
I'm leaning on it being the transmission's internal harness based on my findings. Any additional input would be appreciated before I throw a harness at it.
 

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3rd gear is limp mode, both shift solenoids are released.
2nd gear has shift solenoid B operated and A is released.
To me, this proves that B works.
1st gear and 4th gear require the operation of the A solenoid.
If you don't have 1st and 4th gear, the problem is with the A solenoid (the 1 - 2 solenoid).
Check the wiring for that solenoid and there may be separate fuses for the 2 solenoids.
 

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2001 Suburban 5.3L, 310k miles
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The transmission connector is connected to the internal harness then to the solenoids.
Perform a resistance test to confirm continuity from the 4L60e connector to the individual shift and TCC solenoids.
 

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Discussion Starter · #4 ·
Checked the transmission's internal harness and have continuity to all the solenoids and the solenoids ohmed out okay.

I should have clarified that I can manually downshift into 2nd but the truck will always start out in 3rd gear.
 

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3rd gear is limp mode, both shift solenoids are released.
2nd gear has shift solenoid B operated and A is released.
To me, this proves that B works.
1st gear and 4th gear require the operation of the A solenoid.
If you don't have 1st and 4th gear, the problem is with the A solenoid (the 1 - 2 solenoid).
Check the wiring for that solenoid and there may be separate fuses for the 2 solenoids.
Your problem is with the shift solenoids, or what they do when operated.
Here is the sequence:
Font Number Screenshot Parallel Rectangle


As you can see, 1st gear and 4th gear require the A solenoid to be operated.
If the impedance checks out, do you hear the solenoid operate?
If it operates the problem is internal to the transmission.
If it doesn't operate, the problem is outside the transmission. Perhaps a fuse, a wire problem, or a faulty TCM.
 

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Discussion Starter · #6 ·
Your problem is with the shift solenoids, or what they do when operated.
Here is the sequence:
View attachment 173237

As you can see, 1st gear and 4th gear require the A solenoid to be operated.
If the impedance checks out, do you hear the solenoid operate?
If it operates the problem is internal to the transmission.
If it doesn't operate, the problem is outside the transmission. Perhaps a fuse, a wire problem, or a faulty TCM.

Wasn't the shift solenoids or transmission harness. Even though I had 12v at the plug I didn't have any load true load on the circuit to verify that it was operating correctly. I went out and got a test light to check one last time and it lit up dimly. I trace the wiring from the plug back to the ignition switch and for out some moron attempted to splice into the ignition switch wiring with some crappy connectors. After pulling them off the wires were almost split in two. To much resistance in the circuit. I soldered the wires back together and took it out for a test drive, shifted properly and no codes came back.
 

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