Hey guys,

Yesterday I had code P0128 “Coolant Thermostat” pop up. My car is operating at its normal temp as it always does, between 80-95c and not taking any longer than normal to warm up.

Has anyone had similar experiences with this code but not noticing any irregularities?

Does it in fact mean I’m in for a thermostat replacement (which seems to be a nightmare) or could it be a coolant temp sensor?

Cheers

 

From the sticky

https://mbworld.org/forums/w212-amg/...-warranty.html

 

Thanks man!

Does anyone know what the book time is?

 

I recently started experiencing the same thing - 4 times since February and no luck getting it resolved by dealer. Car goes back in this week but I'm not hopeful.
As in your case, coolant seems to warm up normally and stabilizes at 90C.

 

Mine code went away on its own. I've put nearly 500 miles on in the last few days, never came back. Very strange because the oil/coolant temps were normal as always.

 

I believe the way OBDII works is that CEL will go out if the problem that caused it to come on doesn't recur within a certain number of drive cycles. The trouble code will however remain stored in the system for an additional number of drive cycles after which it will be cleared if the problem doesn't recur.

In my case, I've had the CEL go out in as few as three drive cycles, only to come back after a few days or in a couple of weeks. The trouble code that caused the the CEL to come on has stayed in the system though. Also in my case, I've noticed that the CEL only comes on when I'm on a highway after a cold start up. It takes me about 5 minutes to get to the highway from my place so the coolant is partly warmed up at that point. I've never had it come on in city only driving.

The engine running time from start up to the code being generated has been between 11 and 18 minutes in ambient temperatures between 8 and 13C. When the dealer looked at it after the third occurence, the service report suggested it was 'a 1 time occurence due to cold weather'. I know 8C is considered 'cold weather' in some parts of the world, but come on!

 

I think the tstat is in its way out ... time will tell

 

I had that code and saw subtle variations in temps when the car was fully warmed up (in the 80-95C range with ambient temps in the 30-50F range). The car was also slow to warm up to that range, taking 8-10 minutes to get there. The thermostat is designed to get the car up to optimal operating temp as quick as possible (~95C) and keep it there. My code was intermittent at first and would go away for a few drive cycles but eventually it started happening more frequently..

I also started getting the "Coolant warming up slow" message (I forget the exact wording), also a symptom of a thermostat that needs replacement. Once I replaced my thermostat and coolant ('11 E63), the car warmed up more quickly (~6-7 minutes) and stays consistently pegged at 95C.

Hope this helps.
Pete