P0757, D2903 & D2904 tables???

[Mr. P.]

Vehicle is 2003 Silverado SS truck, stock LQ9, TCS 2800 converter, built transmission with shift kit & billet servos.

I've got an intermittent nuisance I'm investigating that I think is converter related - when I'm following slow traffic up a 5% grade at very low speed and low throttle position (like just off coasting) and the PCM decides to kick down a gear it will turn on the SES light with a P0757 code (2-3 solenoid stuck on?). I've had this happen a couple other times in similar driving situations before and I'm suspecting this has something to do with the slippage in my high-stall torque converter... I doubt it is debris in the transmission as it's only 6 weeks since last rebuild. Another enthusiast who tunes with HPT has said he's eliminated the exact same issue by altering the TCC tables, basically he sets all values in the "TCC Maximum" table to 100, and the values in the "TCC Minimum" table to 90:



These are the D2903 & D2904 tables in EFILive, now I'm wondering exactly what they do and searching has not shed much light on the function of these tables, other than I gather they have something to do with how abrupt the TCC is engaged and disengaged???

Anyways any insight would be appreciated, I would like to master this issue and tune correctly rather than just disable the P0757 code.

TIA -
Mr. P.

[joecar]

When this happens, does the GEAR pid show 2nd gear...?

[Mr. P.]

I wasn't logging at the time, but no the transmission went from 4th + locked-up to 3rd and that tripped the DTC code. The PCM did as it was supposed to according to the shop manual and locked-out 4th plus only allowed 1st via manual selection until I scanned/cleared the DTC.

Mr. P.

[joecar]

Does your shop manual show all the conditions that trigger P0757...?

Edit: (...I don't have my laptop right now...)

[joecar]

I'd say it was due to the stall converter's "looseness"...

Circuit Description

The 2-3 shift solenoid (SS) valve controls the fluid flow acting on the 2-3 shift valves. The 2-3 SS valve is a normally-open exhaust valve that is used with the 1-2 SS valve in order to allow four different shifting combinations.
When the PCM detects a 1-2-2-1 shift pattern, then DTC P0757 sets. DTC P0757 is a type A DTC.
Conditions for Running the DTC

• No TP sensor DTCs P0122 or P0123.
• No VSS assembly DTCs P0502 or P0503.
• No TCC solenoid valve DTC P0740.
• No TCC stuck ON DTC P0742.
• No 1-2 SS valve DTC P0753.
• No 2-3 SS valve DTC P0758.
• No 3-2 SS valve assembly DTC P0785.
• No TFP manual valve position switch DTC P1810.
• No TCC PWM solenoid valve DTC P1860.
• The engine speed is greater than 450 RPM for 5 seconds.
• The engine is not in fuel cutoff.
• The gear range is D4.
• The TP angle is greater than 10 percent.
• The transmission fluid temperature is 20-130°C (68-266°F).
• The system voltage is 10-18 volts.
• The transmission output speed is 150 RPM or greater.

Conditions for Setting the DTC

DTC P0757 sets if both of the following conditions occur:

• Condition 1
• The PCM commands third gear for 1 second.
• The estimated gear ratio is 1.6 to 1.8.
• The torque converter efficiency is greater than 0.5.
• The engine torque is 50-400 lb ft.
• All conditions are met for 2 seconds.

• Condition 2
• The PCM commands fourth gear for 1 second.
• The estimated gear ratio is 1.8 to 3.3.
• The torque converter efficiency is greater than 0.5.
• The engine torque is 0-400 lb ft.
• All conditions are met for 2 seconds.

Action Taken When the DTC Sets

• The PCM illuminates the malfunction indicator lamp (MIL).
• The PCM commands 3rd gear only.
• The PCM commands maximum line pressure.
• The PCM inhibits TCC engagement.
• The PCM inhibits fourth gear if the transmission is in hot mode.
• The PCM freezes shift adapts from being updated.
• The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
• The PCM stores DTC P0757 in PCM history.

Conditions for Clearing the MIL/DTC

• The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
• A scan tool can clear the MIL/DTC.
• The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
• The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.

[Mr. P.]

I'd say it was due to the stall converter's "looseness"...

Hi joecar, I think you've replied into the wrong thread. Yes I have been told that my P0757 issue has to do with the converter being loose, and that modifying the TCC PWM tables will correct that but want to understand the function of these tables and what I am doing exactly before I just go and jack with the tables...

Mr. P.

[joecar]

Mr. P.

Thanks, I was in a hurry when I posted. I moved it to the correct thread (here).

Thanks.


I'm not sure exactly how those tables work.

[xlcooplx]

Anyone else ever figure how to turn off the test? Ive read on other forums that it is capable of being tuned out...I just need a way to do so as I got the P0757 code today as well and lost 1st and 4th it appeared...I cleared the code and the truck is back to normal. I would just like to tune it out. Any help is appreciated.

[FeetDry]

Just going on the table titles,.. Min & Max TCC DC, I would agree with you on the engauge harshness.
Do you understand the TCC PWM idea? DC (Duty Cycle) is a percent. As in 100% is full on, no slip. (Or at least is attempting no-slip.) 100% DC is like before there was PWM of the TCC. Of course 90% is very little slip.

It appears your high stall converter is slipping more than what the PCM is expecting. So locking the TCC earlier than it would normally for stock, is eliminating the slip. (And also eliminating the function of the high stall TC.) This approach takes care of the MIL problem, but appears to effect all PWM operation.

There should be a better approach. Something like tuning the PWM tables. I'm not sure if there is a table where you can adj the amount of slip the test uses. That is, I'm sure there is a test setting somewhere. It is a matter of, is that # changable w/ your editor.

Just my $.05. (Typically it would be $.02, but w/ inflation and all,..)

[xlcooplx]

hmm...nobody else? i still havent found a definitive answer.