4L85E TCC Tuning Help

[jlane330]

I've been reading everything I can on here and can't seem to find an answer to some of my questions. A little background:

2006 Duramax Van with 4L85E Transmission
Mild (~40HP) engine tune, Estimate 600 ft lb
75K miles total

Has been running well the last 5 years until last week, when I got a P0894 (Slipping transmission components) code out of the blue. Did not notice ANY slipping issues, cleared the code, and it's reappeared. I dropped the pan, changed the filter and TCC PWM solenoid (just in case), and added new fluid. Old fluid looked excellent when drained, inside of pan was VERY clean, etc. No obvious issues inside. I can drive it around town and no code appears. Hit the freeway and the code pops up while cruising (does not require heavy throttle to cause the MIL). Again, no signs of slipping that I notice (do not have a Tach or Temp Gauge for transmission). I feel like it's related to the TCC as I can be cruising in 4th gear and stomp on the skinny pedal and it moves out very well (no obvious signs of slipping at all). I can't tell if the TCC is locking though or staying locked.

I saved the Freeze Frames that were generated with the DTC. They are .txt files, and in binary format. How do I open these so I can see the parameters present when the DTC was set? The ECM FF are readable, but not the TCM FF.

I see the TCC area of the tune and am a little lost on what to try. I've read a lot about changing the TCC lock-up from PWM to On/Off. Is it as easy as changing {D6031} TCC Solenoid Minimum PWM to be 100 everywhere? It appears that the Maximum PWM table is already set to 100 everywhere.

Recommendations on what to set the TCC Apply Rate to? What are the units for this table? Stock table numbers are between 0 and 12.

Recommendations for {D6035} TCC Apply/Release Max Pressure? Looks like this ramps up as engine torque increases (makes sense), and seems like increasing these values on the lower end of the torque axis and smoothing would mean that the TCC would apply more firmly, perhaps reducing or eliminating TCC slip. Does this sound correct?

How do I change the table scales for Engine Torque? The tables currently go up to 472 Ft-Lbs. What happens if the engine is delivering 550 FT-Lbs, for example? Are the 472 FT-Lbs values used when the engine torque exceeds the table size, or could this be the root cause of the issues? I can't find a place to change this scale but would like to expand the tables to 600 FT-lbs if possible.

I would really appreciate any and all help you guys can provide. I don't feel like the transmission is in need of a rebuild (maybe it does, but my gut tells me something else might be up). I want to make sure that the issue isn't the tune before plunking down money for a new torque converter and tranny. Side note, I've read about others with these vans have issues like this too. They kept replacing torque converters and transmissions and still had issues. I'm not looking for hard core street rod shifting, but can easily deal with firmer shifts than stock (it's pretty soft feeling).

Thank you very much!
Joshua

[ScarabEpic22]

Hey Josh, would you mind posting your TCM tune so we can take a look?

On gassers, I much prefer the "on/off" style lockup on vehicles that can handle it, set the Min TCC PWM table to like 95 or 98 across the board. This can be hard on the lockup clutch, so use with caution.

Engine TQ, if the signal value is greater than the last column value, it will simply use the last programmed value.

[joecar]

Also check if the are any other DTC's...?

[jlane330]

Erik and Joe,

Thanks for the responses. I did some more digging on my issue and here's the progress:

1. Other DTCs. Yes, I had three total DTCs. One was from the TCM (P0894). Another was from the ECM simply stating that the TCM requested the SES light on. Finally, the third was one that I've been battling for the last 5+ years...EGR insufficient flow. In spite of trying various changes in my tune I can't get this to not come up. Of course there is a EGR blocker installed. No other codes present. Would love to solve the EGR code issue one day...

2. I would like to share the TCM tune. What's the best way to attach that file here?

3. I figured out how to datalog and recorded several logs with many of the TCM TCC related PIDs selected. I cleared the codes and started datalogging and driving until I got issues. Good news is that the transmission temp looks reasonable. It hit 196 deg F maximum driving for approx. half an hour down the freeway (75ish mph). This explains why the fluid still looks ok. I don't think I cooked the fluid or tranny with heat...yet. Again, how would I share these datalog files?

4. Of course the SES light came on after a while.

Here's a screenshot of a peculiar (IMO) spot in the datalog. I'd guess this is about the time that I got the SES light on. BTW, can I datalog exactly when the DTC is set? If so, how?



Based on what I see, I was cruising down the freeway (speed constant at 71 mph, rpm constant around 2100 rpm, in 4th gear). Around frame 15350 it appears that the TCC is commanded not to enable (based on the TCCC PID). The RPM remains quite constant whether TCC is ON of OFF. It appears that TCC ON made no difference to the TCCSLIP rpm. Not sure how the TCCP pressure is measured, but when commanded ON, it appears that there is pressure, and when OFF, no pressure is recorded.

My understanding is that slippage could be the result of either the TCC not locking, or 4th gear not holding. TCCSERR seems to indicate that it's the TCC not locking, but not sure how reliable that is. I would assume that if it was 4th gear clutches not holding, that it'd have more TCCSLIP as engine torque increased. What I notice in the datalog is that the TCCSLIP decreased as the RPM and engine power increased. Maybe it's the converter approaching stall speed, so the slip decreases? Anyway, how do I separate these and decide is the trans needs a build or if the converter is the issue? Or, any other ideas on what could be wrong?

Thank you in advance for any and all help!
Joshua

[ScarabEpic22]

Click "Go Advanced" at the bottom of the quick reply box, then you should be able to see an attachments icon (next to emojii and fonts). Tune and datalogs can be added this way.

It looks like in one screenshot the slip error is rising and matching the pressure (I'd expect that, adding pressure to try and control slip), but slip keeps rising. I wonder if you're hitting a slip limit? (I know the Allisons have this, not sure about the 4LxxE family.) TCMPSLIP looks like it's going crazy, but I dont know it that's normal or not as I've never logged it. At the beginning and end of the log, there is significantly more slip occuring TCCSLIP and it looks like it never gets to 0 RPM of slip. Usually a few RPM isnt a big deal, but that looks pretty significant across the board (maybe zoom in and see what the actual slip values are).

[jlane330]

Thanks for the tip on attaching the tune/datalogs. I'll attach them when I get home this evening.

I haven't noticed any slip limit parameters in the tune to set. The only slip limit I know of is in regard to setting the P0894 code. I forget the actual numbers, (-20 to 40 rpm IIRC) but if a slip is detected for a period of time, then it will throw the code. I'd have to look this up again in the FSM for the exact conditions. I have followed some of the diagnostic tests in the FSM. One test that needs to be done is to drive in 3rd and force the TCC lock-up. Apparently this test will tell if it's the TCC or the clutch pack slipping. MY hunch is that it's the TCC, but want to confirm before throwing parts at it.

I have no idea what TCMPSLIP is. Any ideas? It seems to just bang back and forth, full on then full off repeatedly. Not even sure what that PID means.

Ah, the slip at the beginning and end of the datalogs I believe is normal. When the vehicle is at rest and idling, the TCCSLIP = Engine RPM. I believe that TCCSLIP is simply Engine RPM - Output shaft speed. Although labeled TCCSLIP, if there is any slip in the clutches, I believe it would show itself in TCCSLIP. TCCSLIP while cruising down the freeway is fairly consistent. It changes slightly with engine torque, but overall it seems to be more stable. Anyone know what a typical converter slip would be at stall speed? This converter stall should be approx. 1900-2100 rpm. I would assume that stall does not mean zero slip (otherwise a TCC wouldn't be required). My guess is that the TCC isn't working and the slip I'm seeing is the natural slip of the converter at the RPM. Why the TCC isn't working, I have no idea. Could be in the transmission actuation/circuit/seals or in the converter itself (cracked piston, burned clutch, etc).

Thanks again for looking at this! Any and all input is much appreciated!
Joshua

[joecar]

Check for these:
- is TCC brake switch coming on by itself (it's in one of the TSTATE pids)...?
- is ABS detecting rough road and telling ECM/TCM to disengage TCC...?
- are any misfires occurring (which causes ECM to tell TCM to disenage TCC)...?

Also there is a pid GM.TCCMODE which may be interesting, log this also.

4L80E/85E has ISS sensor, so also log GM.TIS and GM.TOS.

Also log throttle position, GM.ETCTP.

[joecar]

Post tune and log files as Erik said above.

[joecar]

GM.TCMPSLIP is a counter, it counts individual slip events.

[joecar]

Log GM.TSTATE03 for TCC brake switch state.

Log GM.TSTATE09 and 10 for TCC off reason.

Log GM.TFMPRS to see what line pressure is doing.