P0740 Torque Converter Clutch Circuit/Open

[tobe1424]

1996
740iL
180K


I went to autozone and they pulled up some codes using their obd II scanner. They are: P0740, P0500, P0420, P0430.

The first one is "Torque Converter Clutch Circuit/Open" and the second one is a vehicle speed sensor.

I have read plenty of threads online. Some say to replace the TC..others say to swap the fluid/filter - although bmw supposedly recommends to never change it - some others say to replace some solenoid. However I am unsure as to what I should do.

When the car is cold, 1st to 2nd gear seems to have some sort of "torque lock". I have heard the term around here. I am assuming this means that the trans does not shift immediately or with delay?

Anyhow, once the car warms up it shifts fine. My ls430 certainly doesn't do this during start up and drive scenarios - it shifts smoothly from the get go. But my e38 takes some minutes for it to start shifting smooth.

My question is, should i change the solenoid, tc, or something else?

thx

t

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i forgot to mention...at times..i do feel a subtle harsh-isssh downshift. at first i thought this could be the motor / trans mounts...but now with these torque converter p code I am confused and paranoid :\

[OptimusGlen]

BMW says the fluid is lifetime, what that means is for the lifetime that they are concerned with it, in other words for the life of the warranty which likely expired long ago.

That said, a simple fluid/filter change may do wonders, it also may expose transmission issues that had otherwise been lurking. In my case I had some minor issues, changed the fluid to Valvoline Maxlife and started having much worse issues. Others have used the same fluid with no adverse effects though. I then took the valve body out and rebuilt it, found a crack in one housing and replaced that housing, rebuilt and filled with Pentosin and it's now working much better.

If I were in your position, I would drain the fluid, drop the pan and the valve body, test each of the solenoids (there are procedures for all of this in a somewhat current thread on here) and check out the speed sensors. Rebuild the valve body if you've got around $200 sitting in your pocket, plus new filter and new fluid, and see where it gets you.

The magnets in the pan will be covered in sludge, that's normal for the most part, but if there are metal shavings you might be looking at a teardown.

[tobe1424]

thanks much for the input!

Although I want to replace the filter and fluid and possibly the valve body, doesn't the P code point more towards a solenoid issue? Assuming that "Circuit/Open" would indicate a possible electrical/solenoid issue?

I guess as you said, I could test each of the solenoid..i wonder how this procedure takes place.

[OptimusGlen]

Yes, but to get to the solenoids you'll have to drop the pan. And to drop the pan you'll need to drain the fluid. You're not going to put the old fluid back in right? And you wouldn't put new fluid in with an old filter right?

[tobe1424]

Yes, but to get to the solenoids you'll have to drop the pan. And to drop the pan you'll need to drain the fluid. You're not going to put the old fluid back in right? And you wouldn't put new fluid in with an old filter right?

I see.

But then this comes to mind: Is the P0740 code vague info? Or does changing your trans oil/filter can actually make a world of difference and fix this code - which again, from a technical point of view seems like an electrical component since the term "Circuit/Open" was used..but then agian, this could simply be a silly assumption of mine.

thx

[psjr]

Not sure where the reader got the Open Circuit from.

P0740 means that the torque converter lockup was detected as not functioning properly (too much difference between flywheel and input shaft speeds when lockup is commanded).

This will be manifested when driving as higher RPMs on the highway, along with a less-connected acceleration feel. There may also be "shuddering" or jolts on the highway from the TC attempting to lock up.
If you get shuddering, meaning the TC lockup has some grip still, you may be able to put in some Dr. Tranny shudder fix and be OK for a few thousand more miles.

[tobe1424]

ECU: GS 8.55, Engine: M62, Transmission: 5HP24, from 01.09.96 till
30.04.97
PCode BMW-FC PCode text
P0705 8 Transmission Range Sensor 'A' Circuit Malfunction (PRNDL Input)
P0715 16 Input/Turbine Speed Sensor 'A' Circuit
P0720 42 Output Speed Sensor Circuit
P0720 106 Output Speed Sensor Circuit
P0731 131 Gear 1 Incorrect Ratio
P0732 132 Gear 2 Incorrect Ratio
P0733 122 Gear 3 Incorrect Ratio
P0733 133 Gear 3 Incorrect Ratio
P0734 123 Gear 4 Incorrect Ratio
P0734 134 Gear 4 Incorrect Ratio
P0735 135 Gear 5 Incorrect Ratio
P0740 111 Torque Converter Clutch Circuit/Open
P0743 4 Torque Converter Clutch Circuit Electrical
P0748 5 Pressure Control Solenoid 'A' Electrical
P0753 30 Shift Solenoid 'A' Electrical
P0758 33 Shift Solenoid 'B' Electrical
P0763 32 Shift Solenoid 'C' Electrical
P1734 1 Pressure Control Solenoid 'B' Electrical
P1738 29 Pressure Control Solenoid 'C' Electrical
P1743 51 Pressure Control Solenoid 'E' Electrical (M44/M52: Brake Band Electrical)
P1746 104 Transmission Control Module Output Stage
P1747 150 CAN-Bus Monitoring
P1747 151 CAN-Bus Monitoring
P1747 156 CAN-Bus Monitoring
P1748 103 Transmission Control Module Self-Test
P1748 105 Transmission Control Module Self-Test
P1748 110 Transmission Control Module Self-Test
P1750 54 Secondary Pressure Solenoid Circuit Range/Performance (M44/M52/S52/M62/M73: System Voltage
Input Low)
P1761 2 Shiftlock Solenoid
P1765 154 CAN Throttle Valve

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ive jet to drive the car upto 80mph...but at 60 it seems ok.. I could be that the tc is not healthy..but again its weird because it almost seems perfect.sometime at start up the car doesnt't shift all that smooth into second..but it grips..it doesnt spin like a bad tc should...but ive had tc problems in a previous car...this is no where near as bad - yet. I feel like im at a stage where i can predict a future failure..just because of these vague codes..

dont know what to do...i heard tc can get pricey :\

Im just looking forward to replacing what needs to be replaced the first and hopefully last time i bring down the trans oil pan.

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bad thing is that i am driving the car..im paranoid about continuing to drive the car with the faults and old oil might cause irreversible damage.


only weird thing is a sort of notch at times when downshifting to first from second..i iwll drive the car today for about 10 miles and update your guys with more details.

many thx

[kouks]

You can drop your Trans and get your TC rebuilt for $250 plus shipping at Eriksson Industries in CT. Comes to about $300. Google them.

Where did you get the listing of these codes? I need the codes for a 2/98 car. Can you please point me in the right direction.

Your bad shifting when cold is actually no shifting at all. Your Trans is in Failsafe mode and only works in 3rd gear apparently until it gets warm. A VB rebuild, with a rebuilt TC and new fluid and filter may be what the doc ordered. Total cost of about $700 which includes the price of Pentosin or ZF Trans fluid and your labor.

[Mayorchuck]

Not a transmission guy at all but your cold shift sounds like mine, which I believe is normal. More noticeable as the weather gets colder.

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Also, have you had the codes cleared and then checked again after a drive?

[tobe1424]

Not a transmission guy at all but your cold shift sounds like mine, which I believe is normal. More noticeable as the weather gets colder.

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Also, have you had the codes cleared and then checked again after a drive?

Here is the page i downloaded the codes from:

http://forums.bimmerforums.com/forum...shooting-Codes


Thx again, for shedding light on the subject - good to know my trans in in this "safe" mode in 3rd gear upon start up. Other than that, the trans feels smooth.

Im trying to avoid replacing more than what i need. And for now, plan on doing this myself. i am just dazed by what "circuit/open" means. it seems like there are plenty of different codes. So if it was a solenoid, perhaps there was a code for that. But "circuit/open" doesn't tell me much..maybe this means there is a leak? or maybe an electrical issue..


trying to figure out EXACTLY what this code means...cheers..

[RIboater]

Many times the P0740 code comes from the sensor going bad and nothing is wrong with the TC itself. I have had that code for over a year. One somewhat easy way to tell if the TC is is to watch the rpm's at highway speed. You can actually see them jump if the TC is slipping. In my case I just clear the code. Sometimes it comes back in 5 miles, the most recent took 500 miles. I've done one drain/fill/filter on my tranny at around 80k and recently did a drain/flush/filter at around 120k. I've been mixing Valvoline and Castrol. What ever was available. Car drives and shifts fine. Just have to clear the code from time to time. I'll think about replacing the solenoid when I do another fluid change around 160k, but with an avg. 8k miles a year that is a long way off.

[tobe1424]

thx again.

For some reason i also think it is just the sensor going bad. Which is why i am hesitant to buy anything. I am even debating whether or not to change the fluid.

my mind tells me to change it..but the "lifetime" myth thing has me wondering.

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btw...i know i should be using a search button...but are the valvoline & castrol oils just as good as the bmw oils? Is this like comparing GM's synchromesh to the Penzoil synchromesh fluid for manual trans on other cars? They are "up to standards" but its not the same I would think.

[hpbongers]

I just tested all trans soleniods and switches from the comfortable position. Tested at the TCM connector beside the fuse box left of hood. Somone responded with the pinouts to me thread. Search P1734 error. I'm not a 100% sure if it the best though. Read the resistance acording to the 5HP24 manual.MV1-3 are 30 to 34 ohms and the EDS solenoids are 5.2 to 6.8 ohms. TOT is 100 ohms, OSS and TSS is 292 to 358 ohms.

[maddoggyusa]

why were you reading codes? is the check engine or trans light illuminated on the dash?

I would clear the codes and see if they come back. I often have a lots of odd-ball codes come up and clear them and never see them again. If they keep coming back and turning on a light on the dash... then yea maybe spend some time on this. If no lights on dash and driving fine, I wouldn't worry about this.

[tobe1424]

well my pixels on my dash are shot but I can tell something is being projected. I don't see a check engine light..although I assume the "check engine" light shows in my pixels.

So i went to autozone. the ran the codes and pulled 2 catalytic codes and the TCC code along with the wheel speed sensor code.

But what is weird is that the tranny seems ok. But i guess i now want to change my fluid since its been 180K on original fluid.

[Mayorchuck]

well my pixels on my dash are shot but I can tell something is being projected. I don't see a check engine light..although I assume the "check engine" light shows in my pixels.

So i went to autozone. the ran the codes and pulled 2 catalytic codes and the TCC code along with the wheel speed sensor code.

But what is weird is that the tranny seems ok. But i guess i now want to change my fluid since its been 180K on original fluid.

No, it does not. Check your owners manual for a list of warnings that show up as a text on your cluster. You should have a Check Engine Light on if you are getting 'current' codes. Does the CEL come on when you first turn on the key? As stated twice now, I strongly suggest you go to Auto Zone and have them clear the codes. Drive you car for a day or two and have them checked again to see what, if any, codes have returned.

Is this car a recent purchase? Any past maintenance records?

[maddoggyusa]

the check engine light is a separate icon... you'd know if it was on. those codes you found could be 2 years old and tripped when the battery voltage was low. clear them and don't worry about it unless a check engine light or transmission light comes on.

changing the fluid on a transmission with that many miles can cause some issues. The biggest problem you run into is the new fluid might all of a sudden start leaking out of places (like front and rear main seals) where it's currently not causing any problems. Old dirty fluid is thick... new fluid is thinner. If it leaks really bad, then you'll be spending thousands of dollars. Lots of people will say unless you changed the fluid regularly (or the fluid is in very good condition), don't change the fluid. Even if the fluid is old and dirty and it's driving ok... just leave it alone. The stickers do say "filled for life".

http://www.freerepublic.com/focus/chat/2713202/posts

original article here... http://www.freep.com/article/20070501/COL14/705010379/

[tobe1424]

ahh i forgot to check for the cel. let me go put my ignition on 2 and check to see the bulb is there.

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i am with you on what may happen if i change the trans fluid at this many miles.

However i would think that if i change the trans fluid...the clutches may have a happier life

[740iSport303]

I've dealt with the P0740 code myself and tried every fix suggested above and nothing fixed it until I replaced the TC. Then it was gone for good!

[tobe1424]

i have not dogged the car hard enough to detect any slippage. this is due to my drivers side lca/uca and sway bar link bushing are gone. the shimmy effect is killing me!

But i have driven the car for about 30 miles and i did not note any slippage. I do very seldom sense a "not so smooth downshift to first gear" - but then again i am wondering if this is all my suspension moving around since weight is transferred to the front when braking.

I am still dumbfounded by the "Circuit/Open" P0740 code description. There has to be insight as to what this means.

What i find asking myself - wishful thinking in this case - is, how about the sensor itself malfunctioning?

Also, when i turn the key, I do not see my check engine light up.

I see the text on the cluster..but with ignition key on 1 or 2 position..light never comes up.

I may be comparing apples to oranges but with my Hondas, I would put the ignition key on 2 and all lights on the cluster would light up.

If by any chance the check engine light did not light up, this was usually a telltale sign that someone removed the bulb from the CEL in order to sell it to a newbie..I wonder if this is the case on my end now with the e38 :\

thx

[Jamesbond740il]

These cars have a warm up cycle for shift points, its intentional durring warm up. If you think a speed sensor is bad, replace it. TCM gets information from them to decide how to shift rathar than a default shift point. I've had an e38 not shift properly and skip gears because of a rear speed sensor.

[tobe1424]

These cars have a warm up cycle for shift points, its intentional durring warm up. If you think a speed sensor is bad, replace it. TCM gets information from them to decide how to shift rathar than a default shift point. I've had an e38 not shift properly and skip gears because of a rear speed sensor.

hmmm...so it very well could be the speed sensors triggering the other lights?


How about my CEL? Why does it not illuminate when i turn my ignition?

Or does this light only come out when there undoubtedly a mechanical problem?