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Old 07-23-2018, 12:37 PM   #16
tomj76
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Re: Torque Converter Clutch code P0741

I've taken two more trip over the last month and had no issues with the TCC code.
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Old 11-18-2019, 12:47 PM   #17
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Re: Torque Converter Clutch code P0741

New update:

The new Torque Converter did not permanently resolve the P0741 code. I've been getting it randomly on various trips over the past year or so. It seems to be related to driving conditions that require a lot of TCC apply/release cycles, but it isn't a sure thing. I seem to get the error code more often when driving through mountains or highly congested traffic, but I can drive through those conditions without getting the code.

When the code occurs it always causes the PCM stop attempting TCC lockup until the vehicle is stopped and cools down.

This happened on my most recent long trip, the code was set while driving to the destination and and again when returning. It started within 200 miles of the start of the trip and within less than 100 miles during the return.

However, on the return trip I did something I've never done before. Since I had my scan tool with me, I erased the codes after the P0741 appeared. Erasing the codes also resets the TCC "lockout flag" so that it can be used again. That's great, but the error would reoccur immediately (within seconds, not even the "five try rule" noted previously), but only if there was TCC activity. After some fooling around I was able to reset it and then set up the scan tool to report TCC apply ratio, engine RPM, and Transmission Turbine RPM before the error occurred again so that I could see what conditions might be causing the error.

What I found was that the TCC would re-engage without any errors and stay engaged for long periods of time over several miles of driving, but the error code was reported the moment the TCC was released. This is the complete opposite from what I expected.

Since the P0741 code is an error stating that the PCM is not detecting TCC lockup, which implies an attempt to engage the TCC has failed, I thought this would register when lockup failed, but instead the error code is reported when the TCC was released after a successful apply.

So, no error occurs if the PCM never attempts to engage the TCC, or if the TCC is engaged and the conditions for TCC release (zero throttle, down shift, brake apply) are never seen by the PCM.

The other point of interest is that after a dozen or two code resets and about 100 miles of driving, the TCC started working normally again, and P0741 never occurred during the rest of the trip (another 300 miles).

I don't know what is going on, but this certainly fills in the picture a lot more. The fact that it starts randomly, but also can start working again suggests that there is an intermittent problem, but whether that is electrical or hydraulic remains to be seen. I doubt that this is an issue with bad o-rings or anything to do with the clutch itself.
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Old 11-20-2019, 08:42 AM   #18
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Re: Torque Converter Clutch code P0741

What I don't know about transmissions would fill the cloud, but I have experienced this code twice on the Winney. Once at about 215K, once at about 480K. In both instances the clutch friction packs were "replaced". The first incidence by replacing whole tranny, the second by doing a rebuild in local shop.

As I understand: The torque converter is filled with fluid from the internal pump, and the pump is driven through the various clutch packs from the converter,... as the packs wear (and lose thickness), there is less pumping pressure to fill the torque converter.

Things go down hill quickly from there ....

Even with clean Mobil 1 fluid, I don't expect much over 200K miles before another rebuild and friction pack replacement.
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Old 01-03-2020, 11:49 AM   #19
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Re: Torque Converter Clutch code P0741

Took it on another long trip, and it did the same thing again, on both legs of the trip.

It happened each time after 30 minutes of driving, after getting to road conditions where I was cruising at ~70 mph.

It hasn't done this on any short trips (i.e. less than 30 miles).

When it did it during the "to" trip, I tried to reset the PCM to get the TCC working again, like I did on the return trip back in Nov, but the code would reappear as soon as the codes were reset. I tried for about 40 minutes and decided to let it be after that. I noticed that the EPC (electronic pressure control) was "locked in" at 60 psi once the code was set, and would only occasionally move to a different pressure, even when stopping. I've read that the EPC is supposed to modulate with load conditions, and I've see this too while driving the van with the scan tool connected.

On the drive back, the code occurred again, but this time I was able to reset the PCM and restore operation of the TCC. I noticed a few things this time:

- Before the code occurred, I noticed that engine RPM stayed high rather than dropping in driving conditions where the TCC would normally lock up. In fact, I was watching the TCC% PID go to 100% without any corresponding drop in engine RPM when the code occurred. This confirms that there really is a malfunction and the PCM is correctly setting the code since it is specifically looking for a difference between the engine RPM and transmission turbine RPM when the clutch is commanded to close.

- After the code was set, but before the reset, the EPC was stuck at ~60 psi and the transmission fluid temperature increased to 180 - 210 degF, which is probably due to the energy from fluid friction in the torque converter without the clutch operating.

- After resetting the PCM, the EPC pressure reading started modulating again and TCC engagement seemed to require about 54 psi to occur. Once the TCC started working again the fluid temperature fell to 150 degF and stayed there except when climbing long grades where the clutch has to be released by the PCM. I had previously thought that overheating fluid might have been the cause because when I'd read the fluid temperature PID after the code it was always going up.

Just like in Nov, the van never set the TCC code again during the rest of the trip (a total of 500 miles).

I believe it could be either a hydraulic control issue or an electrical issue, meaning either the TCC solenoid or EPC solenoid are malfunctioning, the valve body is sticking, or there is an issue with electrical connections either in the transmission or PCM.

I don't believe that it is a problem with worn friction surfaces since the TCC is new and it is only 70,000 miles since it was rebuilt, plus the measurements that I took of the friction plates showed very little wear when compared to the new ones.

I just don't understand with any of the potential causes why I can reset the PCM and get normal operation for such extended periods without any reoccurrence.
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