2001 BMW trouble codes P0128

firestar · **Joined:** Mon Dec 10, 2007 7:50 pm **Posts:** 2

Hi, i have a 2001 BMW 325CI 2.5 liter engine, the P0128 came on a few days ago and i reset the code, and it came on again today. The water temputer gauge is at normal half way mark in the center of the gauge. I check the fan blade, and it is turnning. Can anyone help me with this problem, and what i can do to fix it. Thanks

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Mohawkmtrs · **Posted:** Fri Jan 11, 2008 8:43 am

Thermostat.

The dash guages are not that accurate.

johannes · **Joined:** Thu May 29, 2008 11:50 am **Posts:** 1

Most probable is a wide open thermostat. The p0128 code tells you that your engine has not attained the proper running temperature within the design time limit, therefore your engine is running cold. A cold engine means your engine parts have not expanded normally from the heat generated and will wear faster. If it isn't the thermostat, maybe it is your fan running too much too often. There are other possibilities for a cool engine, but I would check the thermostat. You can take it out an drop it in a pot of water and heat the water. Check the water temperature and see whether it opens at the proper temp or too soon.

Darkrooms · **Joined:** Thu Mar 29, 2007 9:44 am **Posts:** 1424

MM said more with less: Thermostat. nuff said

MECHANICMIKIE · **Joined:** Mon Aug 25, 2008 4:30 pm **Posts:** 1

I own an 05 Jetta TDI. 70k and PO128 popped up. I used My Snap-on brick scanner. If you can rent an OBD2 advanced scanner it will work. Connect to your BMW and use the live data stream feature. Look at the Coolant temp. Mine would fluctuate from 167F- 173F. I took My fluke IR temp. Use can use any Point and shoot Temp gun. I had 185F at the thermostat housing and the Scanner showed 168F.
I inspected the plug to the coolant sensor. Sometimes if the plug is full of water etc. It can cause bad readings. The plug was clean.
I installed the new coolant temp sensor and drove around town with my scanner connected. Problem fixed!

The IR temp gun is good to have. You can inspect the thermostat temp to see if it is bad or use the scanner to see if the coolant temp sender is bad. Good luck

asecmt · **Posted:** Mon Aug 25, 2008 5:40 pm

replace the thermostat it should come with the housing and the coolant temp sensor.

stue1957 · **Joined:** Thu Jan 15, 2009 12:50 pm **Posts:** 1

I have the same problem, PO128, the thermostat replacement seems to be the answer. Now for the big question, can a backyard mechanic replace it?

2001 BMW trouble codes P0128

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