I have a 1997 Ram 1500 4x4 with 5.2 engine 123,000 mi. Assume it has 46RE transmission. A P0740 fault will be generated in approximately every 100 miles driven. I have on three separate occasions viewed the freeze frame data recorded at the time the code was generated. Vehicle speed was 52, 55, 58 MPH, engine speed around 1800 depending on vehicle speed. It seems that the code is not generated at freeway speeds.

I have monitored line pressure at accumulator port on transmission, pressure ran around 75 psi at 65 mph with pressure as high as 95 psi under hard acceleration.
Today I tried monitoring the pressure at the overdrive port of the transmission pressure, when in overdrive the pressure never drops below 60 psi and runs and is 65 to 75 psi depending on vehicle speed.

From information I gathered at Sonnax website I have determined that there is a boost valve in the valve body that is supposed to raise the line pressure 10-15 psi when the TCC (torque converter clutch) is engaged. I have never seen a bump in pressure when the TCC is engaged. This leads me to believe there is an issue with the boost valve. The fact that I have not seen the code generated at freeway speeds tells me that the engine speed is high enough at that point that the line pressure is high enough to engage the TCC fast enough to satisfy the PCM.

Before checking pressures I dropped the pan and changed the oil and filter. Oil drained looked very good magnet in pan broken but little to no debris in pan. Adjusted the bands while pan was off. Driving the truck the transmission shifts fine. Without the code I would not know anything was wrong. The TCC feels to engage normally though I suspect that there would be an issue if I was using the truck for towing. I bought the truck a couple of months ago and have put around 1000 miles on it. I do not know it's history.

I am looking for suggestions as to if I am on the right track and/or if there is a different issue I should be looking for.

Thank you

 

IF the TCC solenoid hasn't been changed, think I would start there.

 

I finally removed the valve body and disassembled. No real issues found. No sticking valves and bores in housings are not worn. With regard to the solenoids both the overdrive and TCC solenoids have the same resistance around 33 ohms. I found a spec that states the resistance needs to be between 25 and 40 oms so the resistance is in the middle of spec. They do appear to be original, they have a part number stamped in them 52118500. Looks like two gaskets were used. Do not know why one would do that. Have anyone had solenoids that were in spec. and still were faulty? Anyone installed a Sonnax Zip kit in one of these transmissions? Appreciate any other advice on what I should do before I put the valve body back together and back in truck.

Solenoids, note 2 gaskets at bottom where pick is inserted

 

No idea why there would be two gaskets there..... And ya gotta admit, they are old.... so, while they my test good, that doesn't necessarily imply that they ARE good. If you have new ones, install 'em.

Sonnax makes some good stuff. I think the zip kit used to be called the 'sure cure'. I do believe part of the installation is modifying the valve body so that the the torque converter is charged when the trans is in park. Really not a bad idea. (and it means you can check fluid level in park as well....)

 

Thanks for the input.
My plan is to obtain a new set of solenoids and a Sonnax Zip kit. Has to be a reason for the code being generated. The one thing that bugs me is that I did not find a reason for the absence of a rise in line pressure when the torque converter locks up. The boost valve and bore look good, I really expected to find something there. Hopefully the new parts will make the code go away. Will update when I have results.

 

Update on my code issue
I installed a new Standard Motor products TCC solenoid with OD solenoid. Also upgraded the governor pressure solenoid with a Borg Warner unit and installed a new governor pressure sensor. Installed all parts for the valve body from the Sonnax zip kit. There are some internal transmission parts in the kit that require disassembly of the the transmission that were not installed.The other part installed is a Shift TCC boost valve cover plate which has a larger orifice to aid in torque converter lock up.
So after doing this I still get the P0740 code. I do believe the transmission shifts better.
I might try is raising the line pressure, right now after the transmission is fully warmed up the line pressure is barely 60 psi in D engine at idle speed, it is supposed to be 60-65 psi. After this the next thing would be to replace the torque converter. I still do not see a bump in line pressure when the TC locks up but I don't know for sure that I am supposed to.
I find it interesting that the code has so far always been generated between 50 and 60 MPH. I tells me that once the speed is over 60 mph the line pressure is high enough at that speed to lock up the converter in the amount of time expected by the PCM.
One other thing I found, even after installing the kit the transmission oil level is still lower in neutral than in park so I still check the level in neutral.
Not going to do much more with it in the near future. Will be parking it soon for the winter. Keep it out of the salt.
Thanks for the replies.
Jeff

 

You have provided more than enough info to help us diagnose it and for that I thank you. How did you check the pressure while driving? I'm curious there. I do believe there is a piston (I think it's called the accumulator piston) that likes to break.

 

I have access to an electronic gauge (about the size of a volt-ohm meter) from work so I am able to install a sensor an run a wire harness into the cab, also have used a mechanical gauge with a long hose. Part of the Sonnax kit is an upgraded 3-4 accumulator spring and piston seals, that spring I believe has a tendency to break (mine was not broke). I do not believe this is involved with TCC lock up.
Does anyone know what I would need for a tool that would read what is going on with the transmission?
What I have now will read engine parameters but not the transmission. I would be useful to be able to read when the PCM tells the TCC to lock up.

 

Need a high end scanner like Autel, Maxim, Snap-On, even the HF $1K scanner could do it