Unfortunately, you are not the only one in SD that had this problem this summer with 2388s. We had several at our dealership as well. The best solution I have found is ClEAN, ClEAN, ClEAN the air-to-air aftercooler. Remember, it is the first cooler after the rotary screen so any material that gets by the screen_brush assembly gets caught in the air-to-air first. Add this with the fact that the coolers used on 98 and 99 production combines had a very fine tube and fin arrangement, too fine in my opinion, and the air-to-air would really lose its efficiency, causing the "S4" error code to go off. 2000 models with the more coarse cooling fins plus the higher temp. setting for the alarm have been much better about this, but they still seem to be susceptible to this problem as well. Most of those air-to-air aftercoolers I have been around could be cleaned for a half-hour steady and still have debris coming out of the fins. The best way I have found to clean the air-to-air aftercooler is to run the engine at the mid-throttle stop while you blow out the coolers, using the engine fan as a giant vacuum cleaner, while you blow out the aftercooler. Blow from both directions working back and forth and you will be truly amazed at the dirt that packs into the aftercooler. It doesn't help that the aftercooler is about the hardest cooler to reach from the access door, either, but proper cleaning is a must on these in our terrible SD summer heat. As far as the air cleaners, that is an interesting topic. I have heard of guys with 98 and 99 machines ordering an exhaust pipe from a 2000 and newer production machine that has only the one venturi hole for the precleaner. 98 and 99 machines originally had 2 holes as they had 2 precleaners, but when they were retrofitted to the ductwork setup like the 2000 production machines, only 1 was needed. Guys claim the exhaust pipe with just the one hole have better precleaner efficincy. Case engineering claims it makes no difference, but I know a couple guys who would say otherwise(perhaps the venturi on the old pipe was not working correctly, who knowsIJ). I have seen a few machines with the new style ductwork have problems sealing the air intake duct to the radiator_ccoling housing, drawing very dirty air into the air intake system rather than getting air from behind the rotary screen that has been "precleaned" already.