[535gtxenon]

Had battery drain overnight multiple times. Finally found out the cause is the water pump. After engine is stopped, the pump would continuously run for over half hour, despite OBDII computer shows the temperatures on both the engine and the radiator outlet already below 80 celsius. To rule out it is the sensors, I unplugged both and computer shows temperature below zero, but pump just keeps running. Also monitored the temperature while driving through the "hidden menu", the engine temperature keeps between 96--105 so thermostats works just fine. So for now, the only way to stop it is to pull the fuse in the white box under the hood where the ECU is located.

Read through the forum and found out many had the same issue with the pumping continuously running after car stopped. Some suggests replace the pump. But in my case, I just replaced the pump with a OEM unit 3000 miles ago. The original failed around 950K, so it seems very unlikely a new OEM would fail so soon. Because replacing the pump is not a small job, I would to hear some advices as where else to look at before I commit to another new pump. Is it possible the ECU is giving out wrong signal to the pump? is there a relay for the pump that might stuck? BTW, the OBDII computer shows the pump is spinning at 41RPM after engine is stopped. Could this be the sign that the pump is failling as I would not expect any pump takes more than a second an revolution. Any advices appreciated!