My jeep was doing this thing for the longest time. Basically it would drive fine for 15-20 minutes and then it would slam in to limp mode leaving me with just second and third gear. This went on for months. I replaced the solenoid pack, put in a transgo, replaced the filters, the fluid twice, installed a transmission cooler and even swapped out the TCM with one from a 1500. Nothing seemed to fix it. It started to happen more frequently when I turned corners which told me it was either fluid or a hanging wire. Every time I looked under the car I didn't see any hanging wires. My friend who is a Mazda master mechanic said it could even be a wire near the exhaust that is getting hot and the resistance values of the wire change. I discovered the wire on the passenger side of the transmission (pressure sensor) was not only about eight inches too long, but the loom at dried up and fallen off because it was inches from the exhaust.

The two things I did that seemed to have fixed my issue are that I covered the transmission pressure sensor wire with heat shielding wire loom and I wrapped the turbo down pipe. It was either the pressure sensor wire or the crank position sensor wires giving me an issue. All that matters now is that the issue is resolved.

I hope this helps anyone trying to chase down the transmission limp mode issue. On a side note, my under hood temps are noticeably lower thanks to the wrapped down pipe.

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