Cooling issues with 2008 C300
Thread Starter
Newbie
Joined: Jun 2014
Posts: 4
Likes: 0
2008 C300
Cooling issues with 2008 C300
I have a 2008 C300 with some strange cooling issues that I'm hoping someone can help with. First off, my CEL has been on for a month or so. I pulled the codes and the only one that showed was P0128, I figured it was the thermostat since it would take a little time to warm up in the mornings. There were no other odd issues, so I planned on changing it out once my move was all settled. About 1 week ago it noticed the car would start to get hot when sitting in traffic, close to the 100 mark. As soon as I started driving it would cool down again. This seemed like a cooling fan issue to me. While observing the fan I found it will only stay on when the AC is turned on, and only at the low speed. If I turn off the AC, the cooling fan will not come on at all, even if the temp is past the 80 mark. Additionally the AC won't blow cold air when it gets close to the 100 mark. Question is, could the P0128 code be related to the overheating issue? Could the coolant temp sensor be at fault? And is there a fan relay in these cars? I searched and found the fuse diagram, but no info about what the relays are for. Any other suggestions, would be appreciated.
Last edited by kuroitenpi; Jun 12, 2014 at 10:27 PM.
Thread Starter
Newbie
Joined: Jun 2014
Posts: 4
Likes: 0
2008 C300
Replaced coolant temperature sensor and thermostat this weekend, temp now sits right between 85 and 90. Hopefully P0128 error will clear after a few cold starts. Fan still will not kick in unless ac is on though. Maybe I'm not watching at the right times, maybe they don't turn on until temp is higher (i.e. When driving)? Anyone have any insight into this?
Thread Starter
Newbie
Joined: Jun 2014
Posts: 4
Likes: 0
2008 C300
I replaced the cooling fan and it was working great for a few weeks, now its working intermittently. I was sitting at a light and the ac started to get warm then then temp rose to 100. As soon as I started driving the temp went back down and ac started to cool. I pulled over and the fan wasn't running. I started it later that day and the fan ran ok. Does anybody have any ideas where to look next?
Newbie
Joined: Nov 2014
Posts: 5
Likes: 0
From: farmington, CT
2011 mercedes c300
p0128
i have a 2011 c300 and recently have had the code p0128 come up, i purchased the ect sensor but am having a tough time finding its location. any videos or do your guys know where it is?
Thread Starter
Newbie
Joined: Jun 2014
Posts: 4
Likes: 0
2008 C300
Sebastian, changing my thermostat was the only action that cleared the my P0128, I've heard this from others as well. It was an extremely easy job. If you still want to change your ECT, in my 2008 it was behind the head (closest to the firewall) on the driver's side of the engine. Reach back there and you'll feel it, it's the only protrusion with a wiring harness. It was secured with a T10 bolt. It was a tight fit to get back there, but the L shaped torx key was able to loosen it with no problem. Removed it by hand the rest of the way, pulled out the sensor (make sure and check that the O-ring comes off with it, mine was stuck). Install in the reverse order and bleed the coolant. I have no leaks after 5 months.
