P59 SD Max Pressure Shift Workaround

[lanebaumann]

Hey guys. So after doing some research and emailing support, it appears that there is is no way to disable the max pressure shifts when you fail the MAF. I looked through the repository and it looks like every single OS for P59 PCMs is missing that option. So I am wondering if there is any way to work around this issue or are P59 PCM users forever doomed to have max pressure shifts while in SD?

As a side note, does this still happen in the SD custom OS's? I didn't get a definitive answer from support.

Thanks guys.

[5FDP]

Hmm, I don't think I've had that problem when I fail the MAF to tune speed density. This is on a few 4L60e trucks, don't remember having a issue with max pressure harsh shifts.

[lanebaumann]

Hmm, I don't think I've had that problem when I fail the MAF to tune speed density. This is on a few 4L60e trucks, don't remember having a issue with max pressure harsh shifts.

My truck shifts noticeably harder when I fail the MAF. Even with the VE table dialed in and Dynamic airflow reading extremely close to MAF airflow.

[IARLLC]

Yep. Much of the ECM's understanding of the motor's torque output is based on airflow. Some trans tables depend on this estimated torque. So if it thinks that the MAF has failed it maxes the pressures. If the thing does not offer you a custom SD option.....I don't know what to suggest.

[Montecarlodrag]

Only the calibrations with the parameters available under Transmission Diagnostics go to max pressure when MAF is failed. The other will not, I have tested both.
There are workarounds for this. You can scale the tune or modify the Force Motor Current table to lower shift pressure.
In my experience, P59 trucks with failed MAF shift normally, P01 trucks shift at max pressure.

[lanebaumann]

Only the calibrations with the parameters available under Transmission Diagnostics go to max pressure when MAF is failed. The other will not, I have tested both.
There are workarounds for this. You can scale the tune or modify the Force Motor Current table to lower shift pressure.
In my experience, P59 trucks with failed MAF shift normally, P01 trucks shift at max pressure.

That's weird because I can definitely notice the transmission shifting harder when in SD. I will have to log shift pressures vs torque when running normal vs SD.

It is good to hear that they are not supposed to go to max pressure with a failed MAF though.

[Montecarlodrag]

Sometimes they shift harder because the calculated airmass is different when using VE table.
I'm sure they won't shift at max pressure because I have disabled MAF on many P59 trucks and they shifted nice and soft. On several I even had to raise shift pressure.
On the ther hand, I have had some P01 trucks and they shift brutally when MAF is failed and you don't disable the MAX PRESSURE DTC switch under transmission diagnostics.

[2xLS1]

Not all P01 car or truck calibrations will use max pressure on MAF codes. It is very OS dependent. You have to look in the Trans Diag tab to see if Max Pressure is enabled on P0101. P0102, or P0103 on any P01 OS. I have never seen that switch on any P59 calibration.

[lanebaumann]

Not all P01 car or truck calibrations will use max pressure on MAF codes. It is very OS dependent. You have to look in the Trans Diag tab to see if Max Pressure is enabled on P0101. P0102, or P0103 on any P01 OS. I have never seen that switch on any P59 calibration.

Thats what casused me to look into the issue. I don't have the Max Pressure enables under trans diag. Coupled with the fact that I have noticed harder shifts when in SD I thought that I was stuck with max pressure shifts while in SD. I just need to do some more datalogging while in SD to see why the shifts are harder than when using MAF even though both VE and MAF airflow are dialed in to within 2% error with a wideband.

[IARLLC]

Thanks guys for the clarity on that. I have never paid too much attention to which ones did and did not do it. Now that I think about it P01 rigs bang pretty hard during VE tuning and E38/T42 as well. The P59 rigs are OK. I will have to check for that tab under diag next time. I don't really like breaking u-joints during tuning Thanks again.