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Transmission not shifting gears after replacement, codes P0746, P0868, P1722 and P1778?

Tiny
MALLYBOY
  • MEMBER
  • 2009 NISSAN ALTIMA
  • 2.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 106,786 MILES
This vehicle has transmission noise and after which the owner replaced used transmission assembly and after being assembled, the vehicle stopped shifting gears and it was brought to my workshop and I diagnosed it and detected.

1. P1722: estimated speed signal
2. P1778: step motor function
3. P0746: pressure control solenoid A performance/stuff off
4. P0868: Secondary pressure down.

Then I replaced the valve body from the old gear, and I still used the step motor from the gear purchased because the step motor of old gear was broken. So, I test drove it and it didn't shift gear and I diagnosed it again, it return
P0746, P0868 and P1778. I checked transmission fluid and filter and CVT circuit from TCM to CVT UNIT, all checks okay. What could be the problem of this gear? Is it transmission pump that starves those solenoid oil and TCM is seeing it as a fault?
I attached the screenshot of the diagnostic report.
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Monday, July 25th, 2022 AT 8:42 AM

9 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,643 POSTS
The P0746 code stands for “Pressure Control Solenoid “A” Performance/Stuck Off if this not working it will not operated correctly, also I seen the PC1729 no speed signal which will cause the same issue. So I would replace the pressure control solenoid and the VSS sensor or make sure they are connected. Also check the main transmission electrical plug for dirt or corrosion. Here is the location for both in the diagrams below. Check out the diagrams (Below). Please let us know what happens.
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Monday, July 25th, 2022 AT 4:55 PM
Tiny
MALLYBOY
  • MEMBER
  • 309 POSTS
Okay! Thanks once again, I will change the vehicle speed sensor and also the Pressure control solenoid A as you said though you didn't show me the location of pressure solenoid A on the control valve but where I am looking at is the Transmission Pump since there are fault codes P0746 and P0868 indicating pressure issues because low pressure from failing transmission pump can make the computer to see the Pressure switches as being faulty whereas there's no oil pressure from the pump to operate the Pressure switches. Please show me how to test the TRANSMISSION PUMP while the engine is idling?
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Tuesday, July 26th, 2022 AT 2:00 AM
Tiny
KEN L
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  • 47,643 POSTS
Here you go, this is how you can check the line pressure in the diagrams below.
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Wednesday, July 27th, 2022 AT 12:17 PM
Tiny
MALLYBOY
  • MEMBER
  • 309 POSTS
I have tested the pump by removing the hose from transmission housing to cooler housing and it checked okay. I test drive the vehicle and it didn't shift and I re-diagnose it and
P1778 step motor, P0746 and P0868 returned back, is it not the step motor that is causing these codes to trigger?
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Thursday, July 28th, 2022 AT 9:00 AM
Tiny
KEN L
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  • 47,643 POSTS
It sounds like the used transmission is bad. How does the fluid smell?
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Thursday, July 28th, 2022 AT 10:27 AM
Tiny
MALLYBOY
  • MEMBER
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It sounds like the used transmission is bad. How does the fluid smell? I replaced Nissan recommended CVT OIL. So, I am looking at step motor, pressure control solenoid A and B. But please is there a way to used DDM to test stepper motor and those pressure control solenoid?
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Sunday, July 31st, 2022 AT 2:29 PM
Tiny
KEN L
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Yes, the solenoids are pretty straightforward, two terminals connect a DVM to each and measure the OHMs it should close to zero. Also, you can put 12 volts to them, and you should here a click telling you they are working. The stepper motor and will need to go into the scanner prompt to see they offer that option.
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Monday, August 1st, 2022 AT 1:20 PM
Tiny
MALLYBOY
  • MEMBER
  • 309 POSTS
Hi,

Thanks once again, I have been searching for transmission valve but I could not get, so I want to relearn the Transaxle and see if it changes anything or eliminate those fault codes.
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Wednesday, September 28th, 2022 AT 1:37 PM
Tiny
KEN L
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Okay, sounds good. Let me know how it goes or if you need anything else from us to get the problem fixed.
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Thursday, September 29th, 2022 AT 12:57 PM

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