P1189 “Engine oil pressure (EOP) switch circuit” is a transmission code! What is the relationship between the EOP and the Pressure Control Module (PCM) of the 4T65E transmission of my 2003 Buick Century [3.1-V6]. The closest information is related to a 2000 Cadillac, here: http://www.gearchatter.com/viewpost14255.php. Does my Buick even have a Powertrain Control Module (PCM)? The PCS (pressure control solenoid) is a known factory defect. The transmission shop recognized my irregular symptoms of delayed engagement following a somewhat hard stop. It's a common problem; the solenoid wears out, and fluid bypasses the solenoid, causes the problem. My OBD II DTC Codes read P1189. But what does the EOP have to do with it?