Thank you for that post, I didn't know about that little trick.:thumbsup:The "oil pressure gauge" in your '05 is nothing more than an idiot light. The "sending unit" is a switch that closes at something like 5 psi. When computer sees the switch close, it moves the needle to mid-scale.
I'd check to see if your oil filter is draining due to a bad anti-drainback valve. I believe it has to be up above min press in 5 secs or it will move the gauge to "L."
You can also run the instrument cluster self-test by holding in the trip odo reset and turning the key to on. You'll see all the gauges run through test and then any faults will be displayed in the odo.