Hallo Estebanos,
mal abgesehen davon, daß Du Dich nicht vorgestellt hast, hier ein Lösungsansatz aus dem Cummins-Forum:
P0750 is an LR Solenoid Circuit fault. This indicates a problem with the LR solenoid coil, or the wiring, or the PCM.
This is strictly an electrical fault. The PCM periodically tests all the solenoid coil circuits (typically every 10 seconds). If the solenoid is off, it turns it on briefly (for a few milliseconds) and then turns it back off. If the solenoid is on, it turns it off briefly, and then back on. When the solenoid is turned off, the magnetic field around the coil collapses, which induces a voltage spike on the wire. The PCM watches for this inductive voltage spike. If it doesn't see the spike, it re-tries the test three times. If the test fails each time, you get the Solenoid Circuit fault for that particular solenoid coil (in your case, LR).
So if the solenoid coil is broken internally, you get no magnetic field, hence no spike, hence the fault. If the wire (in between the PCM and the solenoid) is broken, you also get no spike (and the same fault). So the problem could be the solenoid coil or the wire. But note that, in many cases, the solenoid driver chip (in the PCM) fails, so that it either doesn't turn the solenoid on or off properly, or (more frequently) it doesn't properly recognize the voltage spike (so it sets the fault even though nothing is wrong with the coil or wiring).
On the 2010 (and later) models, the engine controller and trans controller are combined in one unit (the Powertrain Control Module, or PCM). Pray that your PCM is OK, because the PCM is a Cummins controller and costs around $1200 or so (ouch!). Note that this PCM is NOT the same as the 2007-2009 Cummins engine controllers, so in this situation, if you opt for a junkyard PCM, it must be from a 2010 (or 2011) truck.
Since your fault has not recurred, obviously your LR solenoid wire (or coil) is not completely broken. I would suspect (and hope) that you merely have a loose or flaky connection on that wire somewhere. Try disconnecting and reconnecting the transmission harness at both ends (at the trans solenoid connector - the main 23-way connector, and the PCM). Often that will clean up a flaky connection. Note that the trans connector has a locking handle / lever that must be unlatched and raised in order to unhook the connector, and it's hard to get to, so it can be a pain.
Or, you can just keep driving it, and see if the fault re-occurs. This is not something that will harm your trans (but if it goes into limp-in [4th gear] don't drive it like that for an extended period, because the torque converter clutch will never engage and you will overheat the trans eventually). If the fault stays away, then all is OK...
Viel Glück, daß es nicht das PCM ist...
Grüße
Clemens
