Error code P0128
02-15-2018, 04:50 PM
#1
Newbie
Thread Starter
Join Date: Jun 2017
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
E350 4matic
Error code P0128
I’ve had my check engine light for about 2 weeks now and diagnosed error code p0128. I installed a new thermostat and last night and still have the check engine light on. I drove it more than 30 miles already but doesn’t seem to go away. I tryed erasing the code but only comes back right away. My temperature shows 147 degrees Fahrenheit meaning it’s very low. I soon need to go for an emissions test but won’t pass with this problem. What should I do?
02-15-2018, 07:21 PM
#2
Senior Member
I haven't dealt with this error code on a Mercedes yet, but in my Chevy Truck the problems lies with the ECT (Engine Coolant Temp Sensor) or the attached wiring.
02-15-2018, 07:47 PM
#3
MBWorld Fanatic!
Join Date: Oct 2005
Location: Chicagoland
Posts: 4,920
Received 1,616 Likes
on
1,186 Posts
2014 E550-sold 😩
How are you measuring the temp in Fahrenheit? The dash gauge is in Celsius. In any event I don’t believe your new thermostat is working properly. Was it an OEM part? They are not cheap. Your temperature is so low reflecting an open thermostat condition (failure). Your CEL will not go away until this is fixed. Once again, I think your new thermostat is bad.
02-15-2018, 09:57 PM
#4
MBWorld Fanatic!
Join Date: Feb 2014
Location: MA
Posts: 6,080
Received 1,467 Likes
on
1,148 Posts
2008 E350 4Matic, 2011 E350 4matic
Yeah, try it again. I believe Wahler is the OEM maker of it. I've replaced mine and the new one was fine. It was around $70 on Amazon.
02-15-2018, 10:04 PM
#5
MBWorld Fanatic!
Join Date: Jan 2009
Location: V E G A S
Posts: 9,067
Received 1,730 Likes
on
1,380 Posts
1922 Ford Model T / no OBD
Was it a thermostat or electro-valve?
Code not allowing clearing would indicate the 2nd.
Code not allowing clearing would indicate the 2nd.
02-16-2018, 01:49 AM
#6
Senior Member
Go to Youtube and look for a video by South Main Auto Repair with title 'My Red Hondoo has a P0128 (and it's not the thermostat)'. Scan data shows car was warming up and all of a suddden the CTS dropped the temp reading drastically (temp didn't really drop as indicated by the CTS).
02-16-2018, 12:54 PM
#7
Newbie
Thread Starter
Join Date: Jun 2017
Posts: 4
Likes: 0
Received 0 Likes
on
0 Posts
E350 4matic
My OBD scanner gave me the reading in Fahrenheit. Converting it into celsius is about 67 degrees Celsius. It should be working properly since I did purchase OEM from the Fcpeuro.com
I don’t understand how it is low on my gauge it shows 95 degrees celsius for the coolant temperature.
How are you measuring the temp in Fahrenheit? The dash gauge is in Celsius. In any event I don’t believe your new thermostat is working properly. Was it an OEM part? They are not cheap. Your temperature is so low reflecting an open thermostat condition (failure). Your CEL will not go away until this is fixed. Once again, I think your new thermostat is bad.
Trending Topics
02-16-2018, 04:41 PM
#8
MBWorld Fanatic!
Join Date: Jan 2009
Location: V E G A S
Posts: 9,067
Received 1,730 Likes
on
1,380 Posts
1922 Ford Model T / no OBD
I had several scanners with live data giving me false reading. TorquePro is telling me my exhaust DPF is reaching 1300 psi occasionally. 
I would confirm it with infra red to start.
And again, if you have electrovalve, it is computer that tells it when to open.
I would confirm it with infra red to start.
And again, if you have electrovalve, it is computer that tells it when to open.
03-12-2018, 02:45 PM
#9
Fabi139,
Not certain if you still have the code but I had a similar issue (it did go away eventually). I believe it is tied to the emission group so it's a bit stubborn. Here was my experience:
https://mbworld.org/forums/glk-class...orn-p0128.html
Not certain if you still have the code but I had a similar issue (it did go away eventually). I believe it is tied to the emission group so it's a bit stubborn. Here was my experience:
https://mbworld.org/forums/glk-class...orn-p0128.html
12-15-2023, 07:18 AM
#10
Newbie
Join Date: Dec 2023
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
c180
My c180 gives this error nearly every month, i googled the p0128 code and it says about cat. converter, but my service man says that it can cause o2 sensor, so i changed the sensors but it still continues.. I think this is chronical problem of my car 
12-15-2023, 09:54 AM
#11
Super Member
I have this same error and tried to change my own thermostat however it is a very involved task since on my engine you also have to remove the wiring harness. So my car is going to MB to change out the thermostat and pay to have this done as this one is over my head.
Anyways, you may have an issue related to the amount of coolant in the system and the only way to hack it is to do the following. Your system is "under" pressured and since there maybe air in the system, it's not allow the temperature to rise. One way to help with this is to fill the coolant without placing the full cap on the system and wait for the bubbles to emerge. This is dangerous but of course less if you already used a coolant machine which MB uses to charge up the coolant system.
Anyways, you may have an issue related to the amount of coolant in the system and the only way to hack it is to do the following. Your system is "under" pressured and since there maybe air in the system, it's not allow the temperature to rise. One way to help with this is to fill the coolant without placing the full cap on the system and wait for the bubbles to emerge. This is dangerous but of course less if you already used a coolant machine which MB uses to charge up the coolant system.
12-15-2023, 10:19 AM
#12
MBWorld Fanatic!
Join Date: Feb 2014
Location: MA
Posts: 6,080
Received 1,467 Likes
on
1,148 Posts
2008 E350 4Matic, 2011 E350 4matic
My c180 gives this error nearly every month, i googled the p0128 code and it says about cat. converter, but my service man says that it can cause o2 sensor, so i changed the sensors but it still continues.. I think this is chronical problem of my car
