I have a 2010 Mercedes Benz E 350 4Matic,my engine malfunction indicator light is on and my OBD II diagnostic scanner displays P0128 01/01 code (Coolant temp below thermostat regulating temp).
I have checked the gas tank cap to make sure it is firmly closed and radiator to make sure I have sufficient coolant . I remember not turning off my engine on time the last time I filled up my as just before the light came on so I am not sure if this is related to the gas cap or radiator thermostat. Any assistance on this will be appreciated before I take the car to the shop.
Is it just the code, or does the coolant temp. gauge on the instrumental panel show low temp.? What is the coolant temp. when this happens?
If the coolant temp. is low, then there is no culprit but a sticking/faulty coolant thermostat (or non installed at all), provided all electronics are working properly.
Thank you for the response.
The Coolant temp goes up to 80 F or a little higher when the warms up.
I was thinking of trying to clear the error code to see if it recurs?
You sure it's 80F not 80C ? If it is 80F, then it certainly is something wrong with the coolant circulation and the thermostat has to be taken care of.
And no, error codes should not be cleared before making sure of the detected problem and fixing it first if it exists. It would show up again anyway. Such low coolant temp. is bad for in several areas.
The only DIY I know for this is asking the local dealer, or an authorized parts shop, about the standard rating of the thermostat for your car and compare it with the coolant temp. you get once the engine is fully warmed up. If they match or it goes higher than the standard rating, then the error code you're getting in not because of the thermostat. Driving a couple of minutes without hammering the engine after a cold start should raise the coolant temp. to the standard rating.
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