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PO740 Help

  #1  
Old 07-12-2009, 05:56 PM
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A friend who is a transmission specialist rebuilt the transmission in my 2000 Chrysler Town and Country 3.3liter engine. It has about 170,000 miles on it and was showing the PO740 code when he said it needed to be rebuilt. He assures me that the transmission was bad and even if it were not, it would have only been a matter of time so I'm okay with the transmission having been rebuilt. The problem however, is that he can not get the PO740 code resolved. It runs fine but each time it's reset, it reappears after about 25-40miles. I can't get it past emissions to get tags on it so it is useless to me at this time. I don't think the friend knows how to resolve the problem and is now working through a process of elimination. It is becoming more and more costly for me. Please give me some suggestions.
 
  #2  
Old 07-12-2009, 07:29 PM
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Your torque converter is not locking up as it should. When you get above about 35 mph or so, the torque converter should lock up. That error code is stating that it is not happening. There's a clutch built in to the torque converter to lock it up on command from the Powertrain Control Module (engine computer).
If your transmission was in bad enough shape to require rebuilding, the torque converter should have been replaced. As a transmission goes bad, it can tear itself up inside and little pieces of metal start circulating in the fluid. Those pieces of metal can get inside the torque converter and mess it up too.
The only way to replace the torque converter is to drop the transmission out of the car again. It's located between the engine and transmission. You need to sit down and have a heart-to-heart talk with your friend. Find out if he replaced the torque converter and if so, was it a new one. If so, there may have been a guarantee.
If he didn't, then he should have. Since you would have paid for the new torque converter in the first place, you should pay for it now but your friend owes you the labor.
Good luck.
 
  #3  
Old 07-12-2009, 08:39 PM
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  #4  
Old 07-12-2009, 09:11 PM
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Thanks to you both for the reply. I thought he said he replaced the converter but I'm not certain. I will speak with him tomorrow. I'm was trying not to sound as if I were questioning him as to respect his knowledge but my van is totally useless without me being able to get tags so I have to press now. I have searched the internet for answers and am amazed that even those with knowledge don't reach out to the net for more answers when they're uncertain.
 
  #5  
Old 07-13-2009, 07:52 AM
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Okay, I spoke with my friend. He did replace the converter with a new converter. He said that he tested and it does go into and come out of lockup, so that is functioning properly. He thinks it is likely a short or wiring problem at this point. He said he's going to find the problem but if anyone has any suggestions, I would still greatly appreciate the input.
 
  #6  
Old 07-14-2009, 10:13 AM
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That code is generated by the Powertrain Control Module (engine computer) by comparing the engine speed to the vehicle speed. With the torque converter locked, that comparison should be a constant ratio. If it isn't, the error code is generated. Now there are a number of other operations that depend on accurate readings of vehicle speed and engine speed, so if the problem is sensor-related, you would probably be seeing other anomalies as well.
The locking will only occur when the vehicle is in third gear above about 35 mph. The locking is controlled by the engine computer based on inputs from the coolant temperature sensor, vehicle speed sensor and throttle position sensor. Again, those things infuence other actions as well and if there was an error in those inputs, it would show up elsewhere. Engagement of the clutch is physically controlled by the clutch solenoid on the valve body. I would ask how your friend is verifying that lock-up has occurred.
You might ask your friend if he has re-set the transmission control computer to go through the break-in strategy. He'll need a Chrysler DRB III scan tool to do that. It might help.
The only other thing I can think is that maybe the torque converter he put in there was bad. I'm sure nobody wants to hear that.
 
  #7  
Old 07-14-2009, 12:30 PM
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It's been so long since we started this journey, I've forgotten the original symptoms. It's been a year since I last had our van on the road. After spending the money on the transmission, we bought a used car so my wife could get back and forth to work so the van was no longer a priority. I do know the PO740 code was present when I was told the transmission was bad a year ago. After the rebuild,when he couldn't permanently clear the code, he thought the problem was the TCM. I bought and installed a used TCM. He definetly doesn't believe the converter is bad. When I mentioned that yesterday, he said he is certain he knows the problem and it's not the converter. He's going to replace the TCP valve and check the wiring harness. I respect him and am don't want to offend just offer suggestions from others who have experience with Chryslers and similar issues. He didn't re-set the transmission but says he will do it this time. I did however have a shop re-set the transmission using a DRB III and got farther then any other time(around 45miles) before the code re-appeared. I don't know how he verified lock-up but if he can't permanently clear the code this time, I'll ask all those questions. Sounds like you and Chrysler Tech above are pretty certain it's the torque converter. I'll keep you posted.
 
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