I have a 2003 Yukon XL2500 with a 6l80 transmission swap that I'm having a very strange problem with. The 6l80 is controlled by an aftermarket controller and the only thing hooked up to any of the original PCM transmission inputs is the transmission temperature sensor. I hooked a temperature sensor up so that the trans temp gauge on the dash would work. The problem is that ever since the swap I get a "transmission hot" message displayed on the cluster when the transmission hits about 170F, despite being set in HPTuners to 260F. I've verified that both in the PCM and IPC it displays the correct temperature when I check with a scan tool. I've checked with a couple different people who repair and modify the clusters and and they assure me that the cluster itself doesn't control that message and that it's just coming from the PCM. From everything I've read in the OEM service manual that does appear correct. On the HPTuners side I've tried maxing out the trans overtemperature settings with no change, I've also tried changing the trans type on HPTuners (not exactly recommended but I'm grasping at straws) and that didn't fix it either. With it set to 4l60e, 4l80e, and non-electric trans the temperature gauge works and the message still turns on about 170F. With it set to a manual transmission or Allison I just don't get any temp reading at all for the trans. I've also tried doing an write entire just in case something was oddly corrupted.
What am I missing here? I never thought the most frustrating part of the transmission swap was going to be a warning message on the instrument cluster!
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