Trans limp mode ?

[tinman]

I noticed that in the stock transmission parameters the trans is set to got into limp mode at 235 degrees. But the O/D lock out is set at 270 degrees. Seems to me it ought to go into O/D lock out before in would go into limp mode (related to temperature). I adjusted the O/D off down to under the limp mode but I got locked out a couple times during normal driving in the summer. I am assuming the temps the ecm uses is in the line as my probe in the pan has never been over 190. I'm not sure I understand the logic of the stock programming here.

[anarchydiesel]

Stock sensor reads from one of the hottest points in the valve body. Usually 30-40 degrees higher than pan temps

[cumminsDK]

I would speculate staying in overdrive would help cool the Trans as in normal mode with selector in drive this is (stock tuning) the only gear the torque converter is locked providing more cooler flow and less heat generation.

[2007 5.9]

Tow/Haul provides the BEST converter strategy and will be your best bet in curtailing any trans temp issues.

I have 2-trans temp gauges...one in the HOT line and stock sensor read (EDGE INSIGHT) and under normal driving converter locked, there is ~20* diff between the two with VB temp being hotter.

With the converter unlocked I can see up to a 50* diff the other way. The converter is you SINGLE biggest heat generator when in fluid coupling mode...

So if you can keep it locked more often then trans temps will be safer.

[anarchydiesel]

agreed^

[tinman]

What I was wondering (not having any problems) is that it seems to me that going into limp mode is a bad thing. It's there to tell the driver something isn't right and to take action for repair. Conversely going into "overdrive off" mode is to speed fluid flow thru the cooler to aid in cooling down hot fluid. It isn't that anything is really "broken" in the trans (although I would argue that if this happens, one should do something to prevent it). The T/C locks as usual in O/D off mod. I remember years ago I nearly got my '98 1/2 ton suck in the sand on the beach. When I got out and on the hwy, it won't go into O/D until it cooled down a bit. So in this case, nothing was broken in the trans, it just got hot. So I would think one would want it to lockout O/D before it goes into limp mode. Which doesn't seem to be the case with the stock parameters.