Transmission not shifting properly

Tiny
PROKOPIS PAPASTRATIS
  • MEMBER
  • 2004 JEEP LIBERTY
  • 3.7L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 160,000 MILES
I just replaced transmission and installed a used one with 39,000 miles. The car shifts twice only and revs go up to 3,000-3,500RPMs without another shift. I wonder if this is a TCM problem or a speed sensor problem. (Code is generic PO 700 and po 731). Previous transmission had a PO 740 code- Torque converter shift solenoid and lasted about 8 months. I did not attempt to replace solenoid because its inside the transmission. When the transmission fluid was getting really hot in the summer the car was shifting 1 to 2 and to 3d with a bang. Every time that happened I was restarting and immediately the problem went away. Please advise. Thank you
Friday, November 12th, 2021 AT 10:38 AM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,127 POSTS
Hi,

The code, P0731, occurs when the PCM detects a first gear’s input speed sensor and transmission output speed sensor. As a result, the vehicle cannot shift properly.

There are a few things that can cause this to set. Something as simple as low or contaminated transmission fluid, a dirty filter reducing line pressure, a TCM that needs to be reprogrammed or replaced, a faulty shift solenoid, and so on.

Are the two codes indicated, the only ones stored? If there are additional ones, let me know what they are.

I attached the diagnostics specific to this code below. Take a look through them and let me know if you are comfortable doing them.

Take care and let me know what I can do to help.

Joe

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Friday, November 12th, 2021 AT 4:14 PM
Tiny
PROKOPIS PAPASTRATIS
  • MEMBER
  • 12 POSTS
Thank you for your reply. I don't have the DRBIII scan tool that Chrysler use nor a lift. Because as I said before the previous transmission had problems (codes PO700-PO 740-torque converter clutch solenoid etc I let go -solenoid been internal to this transmission-. Transmission lasted for 7 months and went bad 20 days ago. I replace with a use transmission with 39,000 miles on it and I got only 1 code PO731. I feel that is unlikely that the new one is internally bad and I suspect that the TCM is bad / 10 pin electrical connector / speed sensors electrical connections. So, I am thinking to buy a recondition TCM that is going to cost me $200.00. Replace the old one and take the Jeep to the dealer and let them do diagnostics according to the service bulletin for PO731, this way I will save a lot of money and I will find out what the problem really is. Also, I wanted to ask you if after I replace the TCM do the dealer has to perform a relearn of the transmission? The TCM will come reprogrammed with the VIN. Your input will be greatly appreciated, Thank you
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Monday, November 22nd, 2021 AT 12:38 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,127 POSTS
Hi,

Certainly, it could be a connector issue or the module. As far as module replacement, if it is a pre-programmed unit with your specific VIN, it should be plug and play. Nothing additional will need to be done by the dealer.

If you have a chance, let me know how things turn out for you. I'm interested in knowing. Also, let me know if there is anything I can do to help or if you have other questions.

Take care,

Joe
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Monday, November 22nd, 2021 AT 7:48 PM

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