Hi I have 2006 E350 and the check engine liht came on , i have a car md scanner and it came up with code P0128 which i think has somthing to do with thermostat, can any one help me out as to how to fix this or any instructions on how to change thermostat any help is super appreciated.

Thanks

P0128 = "Coolant thermostat (coolant temperature below the thermostat regulating temperature)"

The thermostat is on the top of the water pump, at the front of the engine. See the bright spot in the attached PDF photo of my E320 engine. The E350 is probably the same.

Step 1: Check your coolant level and top-up if necessary. This probably isn't the issue, but it is simple to check.

Assuming you scanner has some capabilities to read data and not just report the codes......

Step 2: With the engine off and cold, use your scanner to compare the ECT (Engine Coolant Temperature) value with the Intake Air Temperature (IAT) value. They should both be whatever the local air temperature is, give or take. If they are very different from each other, your ETC sensor may be crazy, rather than the thermostat per se

Step 3: If the ETC reading fails step 2, unplug the connector from the sensor. (It is on the water pump, I presume, near the thermostat. There is one sensor there on my car and I suppose that's the ETC. It's 10pm and I have not tried it.). The ETC reading should now be very cold, since no signal is interpreted as cold.

There is more checking that could be done, including using a wire to loop the sensor cable to create a continuous circuit that would result in a very hot ETC reading, but that may be more than you want to try.

Bottom line is that a new thermostat will cost about $90 on-line, part only.

Access to the thermostat is very good and if you google / youtube or search the various Mercedes forums you'll probably find generic instructions for replacing a thermostat. It shouldn't be hard.