PO1028
Thread Starter
Junior Member
Joined: May 2019
Posts: 15
Likes: 0
From: Michigan
2014 C250 Sport RWD
PO1028
Alright, I have a crazy one for you guys. I have a 2014 C250 and this winter while I'm going to pick my daughter up from the airport (about a 30-40 minute drive) my check engine light comes on. I get back home, and the next day I pull the codes and I get a PO1028 Engine Coolant Temperature Below Thermostat Regulating Temperature code. So I stopped driving it until I got a new thermostat. Bought a new OEM thermostat, but waiting for weather to break to install it. We have a second vehicle so I have been using that. I would only take the Benz out for short drives maybe 5 minutes once every one or 2 weeks. We have a second car and we both work from home so not many miles put on the vehicles. Anyway, we've had a stretch of good weather, and I decide I'm going to install the new thermostat, but went to get gas first. Low and behold on my way back from the gas station, my Check engine light goes away. My temperature reads the same as it always has, so now I wondering if I even need to change the thermostat. Has this ever happened to anyone? Any advice?
Senior Member
Joined: Jun 2016
Posts: 462
Likes: 152
From: Panama City, FL
2020 C300, 2013 C250, 2000 Boxster S
Alright, I have a crazy one for you guys. I have a 2014 C250 and this winter while I'm going to pick my daughter up from the airport (about a 30-40 minute drive) my check engine light comes on. I get back home, and the next day I pull the codes and I get a PO1028 Engine Coolant Temperature Below Thermostat Regulating Temperature code. So I stopped driving it until I got a new thermostat. Bought a new OEM thermostat, but waiting for weather to break to install it. We have a second vehicle so I have been using that. I would only take the Benz out for short drives maybe 5 minutes once every one or 2 weeks. We have a second car and we both work from home so not many miles put on the vehicles. Anyway, we've had a stretch of good weather, and I decide I'm going to install the new thermostat, but went to get gas first. Lo and behold on my way back from the gas station, my Check engine light goes away. My temperature reads the same as it always has, so now I wondering if I even need to change the thermostat. Has this ever happened to anyone? Any advice?
Thread Starter
Junior Member
Joined: May 2019
Posts: 15
Likes: 0
From: Michigan
2014 C250 Sport RWD
It's a common problem on the M271 engine. At low ambient temperatures, the thermostat fails to open fully within a predetermined time, and the ECM flags this fault. If the cause of the problem does not reoccur, it will automatically clear itself. Intermittent sticky thermostat. I would swap it out.
