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      03-28-2016, 09:41 AM   #1
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Coolant temerature sensor

Hey guys, for a few months now I've randomly got these 3 codes (all 3 at the same time). Probably 5 or 6 times in the last few months.

2b59 (coolant thermostat monitor)
2af9 (coolant temperature sensor)
2b5a (intake air temperature sensor plausibility)

My guess is simply the coolant temp sensor that sits right by the thermostat but all the searching I've done on the forum says users also had to replace thermostat to rectify their problems...

Ideas?

(yes, I misspelled temperature in the thread title, get over it)
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      03-28-2016, 09:17 PM   #2
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Might as well replace the water pump too while you are in there.
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      04-08-2016, 12:18 AM   #3
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Quote:
Originally Posted by kb9uwu View Post
Hey guys, for a few months now I've randomly got these 3 codes (all 3 at the same time). Probably 5 or 6 times in the last few months.

2b59 (coolant thermostat monitor)
2af9 (coolant temperature sensor)
2b5a (intake air temperature sensor plausibility)

My guess is simply the coolant temp sensor that sits right by the thermostat but all the searching I've done on the forum says users also had to replace thermostat to rectify their problems...

Ideas?

(yes, I misspelled temperature in the thread title, get over it)
kb9uwu , what was your solution? I received the same 2b59 and 2af9 codes and cleared them, but they haven't come back after ~160 miles. I know they aren't working properly because Carly shows that my coolant temperature is -273.20░C (absolute zero, 0 Kelvin).
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      04-08-2016, 08:13 AM   #4
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I recently had the same code and the thermostat, coolant and vent pipe were replaced by dealer. The thermostat was sticking open, so the coolant was not getting up to operating temp as quickly as it should...better than sticking closed though since you'd be overheating then. I also cleared the codes numerous times and it continued to come back every few weeks. Haven't had an issue since replacement.
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      04-08-2016, 09:14 AM   #5
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Quote:
Originally Posted by TWiTCHY View Post
kb9uwu , what was your solution? I received the same 2b59 and 2af9 codes and cleared them, but they haven't come back after ~160 miles. I know they aren't working properly because Carly shows that my coolant temperature is -273.20░C (absolute zero, 0 Kelvin).
Solution so far has been clearing codes weekly with Carly app

I have a new temp sensor sitting here in front of me, but since I have to remove the intale plenem anyway, I might just pick up a new thermostat while I'm at it. Would be stupid to spend an hour swapping a sensor when it's probably the thermostat all along.

Will report back in about a week!
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      01-15-2017, 04:39 PM   #6
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i know this thread is old but i'm hoping the OP can report back on this status.

I've been having the same problem and so far i've replaced the IAT, thermostat and coolant temp sensor and still get the error code.

I've checked the wiring with a multimeter and as far as i can tell there are no issues. When i look at the intake temp and coolant temp with Carly app the temperatures look about right also.
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      01-16-2017, 02:05 PM   #7
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I think OP actually sold his M3 a few months ago. Have not seen him around here for a bit either.
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      01-18-2017, 03:01 PM   #8
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sounds like a stuck thermostat. I received the same code the other day and noticed the temps taking longer to heat up.
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      02-17-2017, 11:15 PM   #9
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I have a similar code...could a faulty coolant thermostat sensor cause performance issues when driving the car?
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      02-18-2017, 12:55 AM   #10
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i replaced my t-stat at 50k, and searching the forums its not uncommon.
edit: i was only getting 2b59
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      02-18-2017, 12:14 PM   #11
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Ok well it seems like I was actually getting these codes due to an old battery.

Replaced the thermostat, air intake temp sensor and coolant temp sensor and the code still came back.

Did all the electrical tests and checked all the wiring and everything seems kosher.

Battery is 6-7 years old but the car starts right up every time. Replaced it anyways as it's past the normal shelf life of a car battery. And so far it looks like it fixed the issue.
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      02-24-2017, 12:01 AM   #12
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It is weird that I am also getting those three as well, but nothing wrong with it. I might change the battery as well.

2b59 (coolant thermostat monitor)
2af9 (coolant temperature sensor)
2b5a (intake air temperature sensor plausibility)
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      03-03-2017, 01:38 PM   #13
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Quote:
Originally Posted by drifts500 View Post
It is weird that I am also getting those three as well, but nothing wrong with it. I might change the battery as well.

2b59 (coolant thermostat monitor)
2af9 (coolant temperature sensor)
2b5a (intake air temperature sensor plausibility)
BAH! Apparently I spoke too soon, the codes went away for around 1200 miles after I changed the battery but today

2B4C - P0111
Intake-air temperature sensor, plausibility

came back. Back square one it seems
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      05-27-2017, 04:21 PM   #14
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Any conclusions or helpful information regarding these codes?

Problem/Issue:
Engine fan runs at high speed and has a fault code of 2AF9 (S65: Engine coolant temperature Sensor Is Faulty).

What I've Done:
I've replaced the thermostat, sensor, leaking water pump, contaminated belts and replaced the upper and lower radiator hoses.

Result:
Fan continues to run at high speed and 2af9 is present.

other suspicions:
- Could it be related to the evaporator unit (perhaps leaking). I do sense what smells like coolant when I turn the heat or AC on?
- Could it be a blockage somewhere in the coolant system causing the temperature of the coolant to be different from the engine?
- The internal climate control fan does not blow so heat and AC is ineffective.

Next steps:
1. Take a look behind the glove box and look for anything weird (blower motor related things are in there).

2. Take a closer look at the connector that connects to the sensor attached to the thermostat housing.

3. Hand it over to the dealer and pay gobs of money on top of the gobs of money spent (good stuff to have done give 166K miles).

Any assistance appreciated.
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      05-27-2017, 05:38 PM   #15
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Quote:
Originally Posted by L4ces View Post
Any conclusions or helpful information regarding these codes?

Problem/Issue:
Engine fan runs at high speed and has a fault code of 2AF9 (S65: Engine coolant temperature Sensor Is Faulty).

What I've Done:
I've replaced the thermostat, sensor, leaking water pump, contaminated belts and replaced the upper and lower radiator hoses.

Result:
Fan continues to run at high speed and 2af9 is present.

other suspicions:
- Could it be related to the evaporator unit (perhaps leaking). I do sense what smells like coolant when I turn the heat or AC on?
- Could it be a blockage somewhere in the coolant system causing the temperature of the coolant to be different from the engine?
- The internal climate control fan does not blow so heat and AC is ineffective.

Next steps:
1. Take a look behind the glove box and look for anything weird (blower motor related things are in there).

2. Take a closer look at the connector that connects to the sensor attached to the thermostat housing.

3. Hand it over to the dealer and pay gobs of money on top of the gobs of money spent (good stuff to have done give 166K miles).

Any assistance appreciated.
I just had 278D and that was the radiator/ coolant temperature sensor code
I replaced the coolant temp sensor (got one OEM from the dealer for $48) and code is gone and no check engine light.
Sensor is located on top of the thermostat cover under plenum
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      05-27-2017, 05:42 PM   #16
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Quote:
Originally Posted by Cbozz View Post
Quote:
Originally Posted by L4ces View Post
Any conclusions or helpful information regarding these codes?

Problem/Issue:
Engine fan runs at high speed and has a fault code of 2AF9 (S65: Engine coolant temperature Sensor Is Faulty).

What I've Done:
I've replaced the thermostat, sensor, leaking water pump, contaminated belts and replaced the upper and lower radiator hoses.

Result:
Fan continues to run at high speed and 2af9 is present.

other suspicions:
- Could it be related to the evaporator unit (perhaps leaking). I do sense what smells like coolant when I turn the heat or AC on?
- Could it be a blockage somewhere in the coolant system causing the temperature of the coolant to be different from the engine?
- The internal climate control fan does not blow so heat and AC is ineffective.

Next steps:
1. Take a look behind the glove box and look for anything weird (blower motor related things are in there).

2. Take a closer look at the connector that connects to the sensor attached to the thermostat housing.

3. Hand it over to the dealer and pay gobs of money on top of the gobs of money spent (good stuff to have done give 166K miles).

Any assistance appreciated.
I just had 278D and that was the radiator/ coolant temperature sensor code
I replaced the coolant temp sensor (got one OEM from the dealer for $48) and code is gone and no check engine light.
Sensor is located on top of the thermostat cover under plenum
Good to know. That is the one I replaced as well.
No luck. The fan still runs.
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      05-27-2017, 05:51 PM   #17
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Originally Posted by L4ces View Post
Good to know. That is the one I replaced as well.
No luck. The fan still runs.
weird but after googling your code i found this:

2af9 nox sensor, nox signal: coast mode check
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      05-27-2017, 08:36 PM   #18
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Quote:
Originally Posted by Cbozz View Post
Quote:
Originally Posted by L4ces View Post
Good to know. That is the one I replaced as well.
No luck. The fan still runs.
weird but after googling your code i found this:

2af9 nox sensor, nox signal: coast mode check
Thanks for looking around!

Yeah I saw that first part but not the second part (with the 'coast' explanation in it).
Another description I've found for the code is "2AF9 Engine coolant temperature (ECT) sensor ". Ive already replaced that sensor.

And there is a technical service bulletin located at the link below. That TSB is what has me thinking of closely inspecting the connectors.

http://www.autoserviceprofessional.c...ad-bimmer-temp

Edit: The TSB mentions "This could be caused by an internal fault of the coolant temperature sensor or a sporadic connection problem with the temperature sensor connector due to vibration-induced movement.".
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      05-27-2017, 10:58 PM   #19
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Quote:
Originally Posted by L4ces View Post
Thanks for looking around!

Yeah I saw that first part but not the second part (with the 'coast' explanation in it).
Another description I've found for the code is "2AF9 Engine coolant temperature (ECT) sensor ". Ive already replaced that sensor.

And there is a technical service bulletin located at the link below. That TSB is what has me thinking of closely inspecting the connectors.

http://www.autoserviceprofessional.c...ad-bimmer-temp

Edit: The TSB mentions "This could be caused by an internal fault of the coolant temperature sensor or a sporadic connection problem with the temperature sensor connector due to vibration-induced movement.".
you know this is a long shot, I kept reading codes with my NCS and kept coming up as a knock sensor it was 27E2 and I went to my friend and he read with his other tool I'm not sure it could have been a standard reader and my code came up as P013C which is O2 sensor Bank 2 sensor 2... if you want try reading your car with a different scanner and maybe that will shed some new light on your issue.... it helped me find my driver side exhaust leak and I was about to go nuts because s65 does not have knock sensors....
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      05-27-2017, 11:03 PM   #20
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Quote:
Originally Posted by Cbozz View Post
Quote:
Originally Posted by L4ces View Post
Thanks for looking around!

Yeah I saw that first part but not the second part (with the 'coast' explanation in it).
Another description I've found for the code is "2AF9 Engine coolant temperature (ECT) sensor ". Ive already replaced that sensor.

And there is a technical service bulletin located at the link below. That TSB is what has me thinking of closely inspecting the connectors.

http://www.autoserviceprofessional.c...ad-bimmer-temp

Edit: The TSB mentions "This could be caused by an internal fault of the coolant temperature sensor or a sporadic connection problem with the temperature sensor connector due to vibration-induced movement.".
you know this is a long shot, I kept reading codes with my NCS and kept coming up as a knock sensor it was 27E2 and I went to my friend and he read with his other tool I'm not sure it could have been a standard reader and my code came up as P013C which is O2 sensor Bank 2 sensor 2... if you want try reading your car with a different scanner and maybe that will shed some new light on your issue.... it helped me find my driver side exhaust leak and I was about to go nuts because s65 does not have knock sensors....
Wow. That is a good idea. Ill give that a try.
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      05-27-2017, 11:04 PM   #21
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Wow. That is a good idea. Ill give that a try.
yes, won't hurt... it saved me some money because I was going to start replacing coils and they are about $800 for all.
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      05-29-2017, 02:15 AM   #22
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I took out my old sensor and it was coated with a thick build-up. I already bought a replacement but i bet it could have been cleaned.
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