ERROR CODE #p0128 (Thermostat Regulating Temp)

[Talley]

Hi there. I have a 2003 325i and recently got a generic error code on my diagnostic tool.

It is a P0128 code, which reads "Coolant Temp Below Thermostat Regulating Temp".

Does anyone know the cause of this problem? My temp gauge is reading normal (12 o'clock) and I havent seen a major change in performance.

Any ideas?

[Talley]

I talked to a Service Rep and he talked a bit fast, but here is what I got out of the convo:

The error code could mean a number of things. The bottom line is that the engine is not coming up to operating temp (around 68 degrees I think). Some of the problems could be that:

-the thermostat is stuck open
-The coolant temp gauge is bad
-The auxiliary fan is not on at the right time or it is running too much

Ring a bell for anyone? Any tips on a more in-depth diagnostic or DIY fix? I dont want to go to the dealer and pay $600.

Many thanks!

[AG]

Sounds like the thermostat is stuck open. There's a procedure to put the OBC into diagnostic mode, where you will be able to monitor the coolant temp. Once the car warmed up, normal coolant temp should be in the 90 degree C range.

[John in VA]

Have you checked over at http://forum.e46fanatics.com/?

[Scany]

A friend of mine got it and cleared it. Did not return. Then a pulley disintegrated and fried the belt.