Thermostat R&I and code P0115 solved ………
Back in January of this year I posted this…………
http://www.benzworld.org/forums/w220-s-class/1691348-coolant-temperature-replacement.html
During the time between then and now, CEL and code P0115 was not an issue until recently as the weather here became cooler and colder. During the warmer months, all was well. Each time the CEL came on and code P0115 would set, I would just clear the code. I did not associate the engine temperature with DTC P0115 until I read the diagnostic outline more closely……………….
DTC P0115 - Engine Coolant Temperature Circuit Malfunction
“……………………………As the temperature of the coolant changes, the resistance changes on the ground signal to the PCM. When the engine is cold, the resistance is high. When the engine is warm, the resistance is low. "If the PCM detects a voltage condition that seems abnormally low or high, P0115 will set.“
I had overlooked and not considered that my dash temperature gauge was not rising above 60C (140F) at any time. The low coolant temperature had been causing the code to set. I have now driven over 250 miles with many engine starts and stops with the temperature gauge reading now slightly above 80C (180F) and no CEL and no code set.
I am fairly confident that my problem has been solved so this is what I did…………
Use center jacking point and raise car high enough to place 4”x4” blocks under both front wheels…..
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Remove lower left front engine cover…………..
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Open drain valve..............
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Drain coolant into a bucket, I got about 6 Quarts (5.7 Liters)………..
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I purchased the new Thermostat from my local MB dealership for $37.50. About 25% higher than I could have gotten it for on line but when you consider shipping expenses and too, I didn’t want to wait, it was a nearly a wash………..
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Next, release belt tensioner and place serpentine belt down and out of the way……….
![Image]()
Remove coolant hose................
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Remove two thermostat bolts and then out it comes. I had to tap and wiggle it out as it was obviously the original.
New on the left, old on the right, I could not see anything wrong with old unit. They both looked the same to me.
![Image]()
Here is a good view of the horseshoe clip which holds the Coolant Temperature Sensor in place……
![Image]()
New thermostat installed with hose reattached and serpentine belt in place…………
![Image]()
Refill with new coolant, start up motor and warm up to check my work. All looks good, running at a solid 80C + all the time now.
![Image]()
To recap, a fairly easy and straight forward job. Everything is out in the open for easy access. You could eliminate the need to drop the lower front cover to access the drain plug if you had a hose to put over the drain pipe to route the coolant into a container. I’m sure the MB techs would have a short hose especially for that. The red radiator drain knob is reachable from above so if I should have to do this again I might plan ahead to rig up a drain hose setup. That lower cover does fight you a bit when you reinstall it.
Also, this would be a good time to consider replacing that upper hose. Mine was still in good condition otherwise I would have replaced it.
Supporting files attached, torque values etc ………………
Back in January of this year I posted this…………
http://www.benzworld.org/forums/w220-s-class/1691348-coolant-temperature-replacement.html
During the time between then and now, CEL and code P0115 was not an issue until recently as the weather here became cooler and colder. During the warmer months, all was well. Each time the CEL came on and code P0115 would set, I would just clear the code. I did not associate the engine temperature with DTC P0115 until I read the diagnostic outline more closely……………….
DTC P0115 - Engine Coolant Temperature Circuit Malfunction
“……………………………As the temperature of the coolant changes, the resistance changes on the ground signal to the PCM. When the engine is cold, the resistance is high. When the engine is warm, the resistance is low. "If the PCM detects a voltage condition that seems abnormally low or high, P0115 will set.“
I had overlooked and not considered that my dash temperature gauge was not rising above 60C (140F) at any time. The low coolant temperature had been causing the code to set. I have now driven over 250 miles with many engine starts and stops with the temperature gauge reading now slightly above 80C (180F) and no CEL and no code set.
I am fairly confident that my problem has been solved so this is what I did…………
Use center jacking point and raise car high enough to place 4”x4” blocks under both front wheels…..
Remove lower left front engine cover…………..
Open drain valve..............
Drain coolant into a bucket, I got about 6 Quarts (5.7 Liters)………..
I purchased the new Thermostat from my local MB dealership for $37.50. About 25% higher than I could have gotten it for on line but when you consider shipping expenses and too, I didn’t want to wait, it was a nearly a wash………..
Next, release belt tensioner and place serpentine belt down and out of the way……….
Remove coolant hose................
Remove two thermostat bolts and then out it comes. I had to tap and wiggle it out as it was obviously the original.
New on the left, old on the right, I could not see anything wrong with old unit. They both looked the same to me.
Here is a good view of the horseshoe clip which holds the Coolant Temperature Sensor in place……
New thermostat installed with hose reattached and serpentine belt in place…………
Refill with new coolant, start up motor and warm up to check my work. All looks good, running at a solid 80C + all the time now.
To recap, a fairly easy and straight forward job. Everything is out in the open for easy access. You could eliminate the need to drop the lower front cover to access the drain plug if you had a hose to put over the drain pipe to route the coolant into a container. I’m sure the MB techs would have a short hose especially for that. The red radiator drain knob is reachable from above so if I should have to do this again I might plan ahead to rig up a drain hose setup. That lower cover does fight you a bit when you reinstall it.
Also, this would be a good time to consider replacing that upper hose. Mine was still in good condition otherwise I would have replaced it.
Supporting files attached, torque values etc ………………
