[dropit987]

I got the P0128 code a few months ago and replaced the coolant thermostat a few weeks ago. The code went away for a few days but came back on again like usual. My friend who works at the dealership did it for me and a guy he knows told him it was probably the sensor if the code came back so we're going to check that next. Other than the sensor, does anyone have any ideas of what might be wrong or had this happen to them?

 

[robertkhernandez]

This happened to me. When the CEL comes on with that code it is best to replace both the thermostat and the sensor at the same time to avoid this situation.

After couple of full driving cycles the light goes away by itself, no need to re-set it.

 

[dropit987]

Yeah, I replaced the sensor a few days ago and the light has stayed off, and hopefully it stays that way haha. If anyone else runs into this problem, just replace both the sensor and thermostat. It was fairly cheap, only $30 or so for the parts.

 

[DnBtekhnic]

Yeah, I replaced the sensor a few days ago and the light has stayed off, and hopefully it stays that way haha. If anyone else runs into this problem, just replace both the sensor and thermostat. It was fairly cheap, only $30 or so for the parts.

question about replacing the t-stat...after lifting and draining the radiator, do i just fill up the radiator to system specs after replacing the stat and bolt everything back together? the mercedes WIS software has me "Pouring in the coolant and bleeding the cooling system". Thanks.

 

[dropit987]

Yeah that sounds right, but I didn't drain all of the coolant. I just unbolted the tube where the thermostat goes, let it drain as much as it could, replaced the thermostat and bolted it back up. I bled the air and refilled the reservoir to full.

 

[DnBtekhnic]

Yeah that sounds right, but I didn't drain all of the coolant. I just unbolted the tube where the thermostat goes, let it drain as much as it could, replaced the thermostat and bolted it back up. I bled the air and refilled the reservoir to full.

another post stated just draining the radiator completely, replacing the t-stat, then open the cap after filling, let the car run a while then just top it off...gonna try that tonight...

 

[2002c230]

Depending on where the thermostat is located it isn't necessary to drain all the coolant. You can just let what little will drain out of the tubing, because it's located in an elevated position.

 

[DnBtekhnic]

Depending on where the thermostat is located it isn't necessary to drain all the coolant. You can just let what little will drain out of the tubing, because it's located in an elevated position.

ok i am semi successful...i drained all the coolant, detached the hose to the t-stat, replaced the o-ring, replaced the t-stat, put it back together, made sure it was super right, closed the radiator drain, filled the car up with coolant and distilled water, let it run for leaks ALL GOOD, sealed her up and got error codes p0301, p0302, p0303 any ideas? i know they refer to misfire on cyls 1 2 and 3 ... btw i did replace the coil on cyl #3 before i did this...

 

[ASHBURY04]

I have the same problem. Can anyone tell me how to get to the thermostat and also where exactly is the sensor located? thanks

 

[DnBtekhnic]

i just did the coolant t-stat...here are two pics, i am sure the sensor is quite easy...depending on what you want to do you dont have to drain the radiator, i did this because i needed a good flush...but essentially disconnecting this hose, then ubolting the housing (2 bolts) then kinda pulling it out, replacing the rubber o-ring then plugging in the t-stat to the housing, gently reinsert it and rebolt...might take a minute...good luck

 

[ASHBURY04]

i just did the coolant t-stat...here are two pics, i am sure the sensor is quite easy...depending on what you want to do you dont have to drain the radiator, i did this because i needed a good flush...but essentially disconnecting this hose, then ubolting the housing (2 bolts) then kinda pulling it out, replacing the rubber o-ring then plugging in the t-stat to the housing, gently reinsert it and rebolt...might take a minute...good luck

thanks for the info and specially for the pictures but where is the sensor

 

[ASHBURY04]

i just did the coolant t-stat...here are two pics, i am sure the sensor is quite easy...depending on what you want to do you dont have to drain the radiator, i did this because i needed a good flush...but essentially disconnecting this hose, then ubolting the housing (2 bolts) then kinda pulling it out, replacing the rubber o-ring then plugging in the t-stat to the housing, gently reinsert it and rebolt...might take a minute...good luck

Thanks a lot, very helpful pictures

 

[DnBtekhnic]

i posted a DIY thread about the t-stat and flush and i added this...i am pretty sure this is the sensor you are looking for... air intake temp sensor... # 0005422818