mz-man

Ok Everyone, Let's see what you know. I have troubleshot my truck to the best of my ability, and have had it to two mechanics with no results.

I'll start from the beginning. Bought an 04 2500hd 4x4 6.0 4l80e. Noticed above 60 mph the tcc disengages for no apparent reason. DTC history showed cyl 6 misfire. Truck had about 85,000 mi, engine had autolite plugs in it. Replaced with ac delco irridium plugs, new wires from summit. Flushed trans, replaced filter, filled with dexron VI. No changes observed.
Replaced throttle pedal position sensor. No change.
Cleaned MAF Sensor. No change.
Swapped MAF sensor w/ known good. No change.
Replaced PCM - dealer programmed. No change.
Replaced throttle body. No change.

Two mechanics have spent a good amount of time troubleshooting this problem. Third brakelamp ok, cleaned numerous grounds. We have all come to the conclusion the tcc is being commanded off, it is not any mechanical problem in the transmission. What could be causing this?

The kicker to this is when I hook up my 5th wheel camper, everything works perfect. Works perfect whether I have the camper plugged in or not, whether I have tow/haul on or not. I have also replaced the column for another issue, so I have my doubts on it being related to the tow/haul switch. Coolant temp to the pcm stays a steady 195 degrees. Can't really think of anything else.

Thanks in advance for any ideas or insight.

joecar

When the PCM detects misfires it unlocks the TCC.

Try doing a crank position relearn, this aids the PCM in detecting misfires.