You would not get a CEL for transmission problems. If the transmission gets to hot or slips too much you will get a flashing OD light as it happens. In order to see transmission codes you need to retrieve them with an enhanced scanner. The TC (torque converter) locks at highway speeds in 3rd and 4the gear to improve fuel mileage. If the TC is slipping the fluid will become extremely hot (can boil). You can test for lock up by driving on a level hwy at say 55, then gently press the accelerator and see if the RPMs jump or if the speed and RPM increase together (as they should). If the RPMs jump the TC is not locked. Whenever you lift the throttle or tap the brake the TC will unlock for a moment until your throttle is steady.
Line pressure run-away and or cooler cut off happens when a valve in the transmission gets stuck due to age and poor design. These conditions are usually fatal.
There are new valves available (from Sonax) with a revised design that corrects these conditions.
jeff
