service engine soon (p0128)

I would make sure your thermostat is working correctly before jumping to any conclusions. it is the most common failure for the 128 code. Roy

P0128 Engine coolant temp sensor

Change thermostat.

this is obd2 trouble code table,http://www.chinasinoy.com/service/how-to-understand-trouble-codes-37.html it can help you understand the meaning of the code, for this code, you can try this, Verify coolant strength & level. Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary. Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary. Verify proper intake air temperature (IAT) sensor operation, replace if necessary. If the above items check out good, replace the thermostat.

Yep! BMW, thermostat issue.