Performance switch installed

The Tow/Haul button found on some GM trucks tells the PCM when to switch the transmission from normal program mode to performance mode.

The bin file I used for the LM7 had the performance options programmed so I saw no reason not to take advantage of it.  I don’t know for sure, but likely all LM7 PCM files may have these performance options already programmed.

Dash mounted momentary switch (green button). Click to enlarge – use browser back button to return.

The switch between normal and performance is accomplished by sending a ground signal to pin Blue 71 on the PCM.  This is simply done with a dash mounted momentary switch.

Pin B71 is apparently not used on most 2004 PCMs according to the pin layout from Lt1swap.com.  No problem.  We just add a wire to the harness in this location and run this wire to the dash mounted switch.

 

LT1swap.com pin out information. Click to enlarge – use browser back button to return.

Using TunerPro I adjusted the setting  “Shift Pattern Switch Type” as needed to “1 = One switch”.  This is all that was needed to make the momentary switch active.  Then by using LSDroid, I uploaded the saved bin file back to my PCM.

Using TunerPro for editing and tuning. Click to enlarge – use browser back button to return.
LSDroid makes it easy to upload the edited file to the PCM. Click to enlarge – use browser back button to return.

Performance mode changes several aspects of the transmission shifting to acquire later and harder shifts by changing line pressure, higher speed and higher RPM shifting .  This along with the Corvette Servo makes for a more exciting ride.  A touch of the switch sets things back to “normal”  and smooth shifting for cruising through town.

Such a fun driving truck. Click to enlarge – use browser back button to return.

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