2001 300M: error code p0740

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#1
Hi,

I have a 2001 Chrysler 300M with 85000 miles on it. So far, loved this car and never had a problem.

Yesterday, my service engine soon light came on. I pulled into WalMart and got myself an OBDII reader, which told me P0740, which is a transmission/clutch circuit error. I did some Googling on that and came up some people that say this is a speed sensor problem - replace the input and output speed sensors and the problem should go away.

Funny thing is, I was sure it was the transmission because the car shudders slightly when braking, just before you come to a full stop. Not sure if the clutch circuit error has anything to do with this, but it may. Any opinions?

While I was researching, I found some TSBs that are also impacting me, thought I'd see if anyone has the full text of them... (from the AllDATA site):

23-028-03 NOV 03 Body - Windows Creak/Shudder/Chatter When Closing (my front driver's window has always had a loud creak as it's closed all the way, would love to know how to fix this)

08-022-03 JUL 03 Instruments - Brightness Changes in Illumination - this was a minor annoyance but now has become more persistent - my interior lights will flicker from bright to dim! Used to just happen in the daytime, but started happening when it's dark. Really annoying. Doesn't impact headlights or anything. If I roll the dimmer on the dash, it usually stops for a while. Easy workaround but would like to know how to actually fix this once and for all.

09-002-04 JAN 04 Engine - Cold Start Ticking Noise - barely noticeable. In fact, didn't notice until I started up my car in the morning recently and went around to haul the garbage cans to the curb on trash day. Slipped my mind until I saw this TSB. Would like to know if this is something I can ignore.

23-019-01 AUG 01 Power Seat - Moves Fore and Aft Slightly When Driving - I've had this problem since I've owned the car. The dealer said they didn't know what I was talking about and couldn't repro while it was under warranty. Turns out there's a TSB on it. "Didn't know what I was talking about?" Yeah. Anyway, I'd absolutely love any help on fixing this. I understand it's pretty much a couple of new bolts and I'm hoping the TSB has the part numbers so I can whip this one out.

19-001-01 MAR 01 Steering - Loose Feel/Clunking on Turns - I actually have heard this while turning but it's really noticeable on speed bumps. My last car (a Saturn LS2) had this problem except it was really, really bad, so in comparison this is a non-issue. But if it's an easy fix, I'll definitely do it.

Overall, love this car, and this is my first "problem," even though the car drives just fine (so far). I'm worried I'll get locked into "limp" mode, which is where the car doesn't shift out of second gear. I didn't see a TSB on this particular issue.

Thanks, and hopefully info about this car and these TSBs is available.
Steve
 
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#2
2 sources for TSB's one you already know ALLDATA*, the other is your local chrysler dealer,,forget about the NHTSA site they are useless.


* they will also have the needed troubleshooting trees for DIYers..
 

Cheef

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#3
This unit is a A606/42LE.

A P0740 is the same as the old code 38 which is "lockup control". In other words, once a set of criterion are met (cruising at speed, certain TPS position and demands on tranny and engine) the control module allows the torque converter to engage an internal piston which makes takes all the fluid inefficiencies out of the converter and act like it is not there,,,gives you about 3% more efficiency.

During the process of the lock-up the computer looks at the input shaft speed on the tranny vs. the engine RPM. If the 3% drop is not seen, it triggers the code P0740. This means there is a problem.

Possible problems here are: restricted cooler lines, defective torque converter, valve body defect or solenoid pack defect. If any of the speed sensors were defective, seperate codes would be there and you WOULD be in limp-in. A P0740 does not result in limp in but will destroy the trans from heat generated at cruising speed.

The shudder you are feeling code be further indications of the torque converter falling apart...pan drop would yield trash found.

You may really want to get professional advice as eventually without lockup you will roast the transmission. Pressure gauge on TC port and a scanner indicating RPMs on engine vs. tranny would pinpoint problem.

Cheef
 
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#4
Ouch, definitely not what I wanted to hear about the code p0740. I don't have any other codes showing up. Thanks for the detailed info, it's really appreciated.

Any advice on the best bet for this type of diagnostic/repair? I'm wary of the chain stores (Aamco, Midas, etc.) because they always seem to want to replace rather than diagnose/repair, and I'm always worried that the dealer charges way too much.