P261f & p0128 low engine temp bluetec
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2014 glk250
P261f & p0128 low engine temp bluetec
Hi everyone, first time poster here. As the title says my 2014 glk 250 started having an issue where one day the coolant temp randomly dropped to the bottom of the temp gauge. I hooked up my scan gauge and the engine temp was reading 45C. This was weird to me because I still had good heat in the cabin. I checked for error codes (engine light not on) and had the p261f and p0128 codes. My research shows most likely a bad water pump is the cause for 261f, so I checked if the water pump held vaccuum with my mity vac and no issue there. So for that, I'm wondering what's the next most likely culprit? Apparently the p0128 code doesn't necessarily mean the thermostat is an issue, but that the engine just has not reached temperature when it should. Could an issue with the switchover valve not functioning also cause the p0128 & low engine temp? Cheers!
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From: WI
GLK 250
Normal operating engine temp is 87-90*C, so methinks your electronic thermostat has likely failed in the open position.
If you'll be taking the water pump apart, you might want to upgrade the original plastic one (which will fail) to the updated metal one. This will prevent coolant migration issues which would be the death of your GLK.
While you're in there, and depending on your mileage, a new poly-v drivebelt wouldn't hurt.
If you'll be taking the water pump apart, you might want to upgrade the original plastic one (which will fail) to the updated metal one. This will prevent coolant migration issues which would be the death of your GLK.
While you're in there, and depending on your mileage, a new poly-v drivebelt wouldn't hurt.
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2014 glk250
So my issue I'm having appears to be related to the coolant temp sensor. I checked and thermostat appears to be operating correctly (also previously checked water pump for vaccuum). The coolant hoses and reservoir were all very warm as if the engine was at correct operating temperature or very close, and the thermostat appeared to be closed from feeling the upper radiator hose and it being cold. In -20C weather the car could still run a bit over 80C. Since my issue the temp gauge has done everything from being on the bottom when driving, or can be close to 80 but then suddenly drop to 60 then return. I don't have the p261f and p0128 codes after they were cleared and now have p0116 and p0118 for the temp sensor. I have cleared the codes, driven the car and they will come back the next day. The coolant temp sensor looks like an inexpensive and fairly straight forward fix so I will start with that.
I used my Bluedriver to scan all modules and found a lot of codes for several miscellaneous issues including windshield wipers and radio, yet everything is working fine. I'm wondering if p/o had repairs done to the car and the codes didn't go away unless cleared with scan tool. My CEL was not illuminated when the p261f and p0128 codes were present.
I used my Bluedriver to scan all modules and found a lot of codes for several miscellaneous issues including windshield wipers and radio, yet everything is working fine. I'm wondering if p/o had repairs done to the car and the codes didn't go away unless cleared with scan tool. My CEL was not illuminated when the p261f and p0128 codes were present.
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2014 glk250
I should have said it was -20 when the gauge was reading ok, it's been +5 to +10. I did get the thermostat to open when it was idling and I was troubleshooting under the hood and rad hoses felt pretty close yet my scanner said engine temp was 30C. Haven't had any water pump or tstat codes come back & the temp sensor codes have been recurring. If I still have issues after doing that I'll replace t stat
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MBWorld Fanatic!
Joined: Jul 2012
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From: WI
GLK 250
Remember that the T-stat is electronically controlled, it's not just a simple spring valve design that opens/closes arbitrarily. Instead, the ECU control WHEN it opens/closes to help warm up the engine (and get cabin heat going faster) as well as to keep the engine temp controlled at all times.
If it's not responding as well as the ECU would like, you'll have issues. My advice would be make sure you definitively diagnose it and replace it sooner rather than later.
If it's not responding as well as the ECU would like, you'll have issues. My advice would be make sure you definitively diagnose it and replace it sooner rather than later.
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2014 glk250
Happy to report that I replaced the sensor and my issue has been resolved. It was 0C outside today, after a short time of driving, the temp gauge worked its way up to ~85, then lowered to 80C and held after the t-stat opened, didnt fluctuate at all.
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2015 GLK 250 , 2016 GLA , 1976 450SL
Hi , I am doing some trouble shooting on a somewhat similar issue . Is there more than one Engine Coolant temp sensor location ? I am looking just below the brake booster vacuum line connector .There is a hole for the sensor but no sensor ?? This is a 2015 GLK 250 . . First post , I hope I have posted in the correct thread .
Thread Starter
Newbie
Joined: Mar 2021
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2014 glk250
Hi , I am doing some trouble shooting on a somewhat similar issue . Is there more than one Engine Coolant temp sensor location ? I am looking just below the brake booster vacuum line connector .There is a hole for the sensor but no sensor ?? This is a 2015 GLK 250 . . First post , I hope I have posted in the correct thread .
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2014 glk250
Well, my CEL came back on today with the p261F code, even though it's been over a week since I cleared the initial codes and never had it come back. I'm going to guess that since I vaccuum tested the pump and all was well, there must be am issue with the solenoid. Does this code mean the pump is being bypassed all the time or that it's in normal operation?
