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      11-12-2020, 07:03 AM   #1
LakeSurfer
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2B59 coolant thermostat monitoring code question

A few months ago I had a wheel speed sensor go bad. so I plugged my scanner in and while pulling the codes I got a 2B59 coolant thermostat monitoring code on my foxwell scanner but nothing on the dash. I pay very close attention to the car especially engine temps and I never noticed anything out of the normal. so I cleared the codes and post pont the wheel speed sensor a f ew weeks. I went to order the part, forgot which side was bad and pulled to codes again and found the 2B59 was back and yet again nothing unusual with the car and its performance. knowing that temps appeared to be fine I drove as normal, replaced the speed sensor and recently had a TPMS go bad, so again I pull the codes and yay! 2B59 is back.

So the temps have always been in the 200 range when warmed up, i cleared the codes multiple times but this one is persistent. The coolant temp sensor seems to be what the code is telling me is the problem and it doesn't seen like to hard of a job to replace so im sure ill do it shortly, but my question is, why is it throwing a code and nothing on the dash, can the sensor be faulty and still function properly or maybe its intermittent and that's why it throws the code?

im not to concerned with it yet just a little curious.

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-Mark
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      11-12-2020, 07:24 AM   #2
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Could be thermostat is stuck closed and causing longer warm up time.
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      11-12-2020, 08:17 AM   #3
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Quote:
Originally Posted by SAMM3Y View Post
Could be thermostat is stuck closed and causing longer warm up time.
Potentially but that would mean it was in that condition for the past couple years because I haven't noticed anything strange. unless its super subtle. I have noticed that its sometimes fully warmed up right when I get to work or sometimes a mile or 2 away from work but nothing to crazy. I just atributed it to weather.

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-Mark
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      11-12-2020, 05:31 PM   #4
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Yeah I'm not sure how it would know since the thermostat is all mechanical. Maybe someone can chime in who knows more. Maybe it looks for a correlation between engine run time coolant temperature, speed and ambient temp. I have seen this before on my car when I've been reflashing and looking at stored codes but like you I've never seen anything on the dash light up.
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      11-12-2020, 07:36 PM   #5
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Quote:
Originally Posted by SAMM3Y View Post
Yeah I'm not sure how it would know since the thermostat is all mechanical. Maybe someone can chime in who knows more. Maybe it looks for a correlation between engine run time coolant temperature, speed and ambient temp. I have seen this before on my car when I've been reflashing and looking at stored codes but like you I've never seen anything on the dash light up.
I appreciate it. I picked up a new sensor from FCP since I needed to do an oil change anyway I though I could knock them both out.
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      11-12-2020, 08:32 PM   #6
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I had the same code, temp sensor replacement resolved it for me.
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      11-12-2020, 10:04 PM   #7
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Got the same code, no dash light. Changed the thermostat temp sensor and thermostat and noted that the car warms noticeably faster.

Dunno how long I drove with either a bad thermostat or sensor as it was a few yrs of ownership before I ran into the code while loading a tune.

Doesnt make sense that that BMW wouldn't have this trip the dash light.
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      11-12-2020, 10:18 PM   #8
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Quote:
Originally Posted by M43S7RO View Post
Got the same code, no dash light. Changed the thermostat temp sensor and thermostat and noted that the car warms noticeably faster.

Dunno how long I drove with either a bad thermostat or sensor as it was a few yrs of ownership before I ran into the code while loading a tune.

Doesnt make sense that that BMW wouldn't have this trip the dash light.
Yah I've been thinking about this. The dash shows oil temp not coolant but anything connected via CAN does show coolant temperature too and I've never noticed a deviation but like Mark I've seen this code before too only when I have a laptop connected for flash. Thermistors typically don't go out of range a little and they typically only fail when they are subjected to extreme elements like freezing then hot, maybe the m3 only alarms when oil temps go crazy? Seems weird if the coolant temp sensor goes out of range and doesn't throw a CEL.
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      11-13-2020, 12:56 PM   #9
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Changing the thermostat and coolant temp sensor is an easy job with a few basic tools, did it myself a few months ago. Much easier than I'd anticipated. There's a good write-up in the DIY section of this forum.
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      11-13-2020, 04:40 PM   #10
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Had this code a couple of years ago show up intermittently on Carly with no other symptoms (don't recall longer warm up times than usual but I suppose it's possible). Had the thermostat and coolant temp sensor replaced under aftermarket warranty and it hasn't returned. Not sure I notice any material difference in warm up time but it's possible there is.
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      11-14-2020, 09:46 AM   #11
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Quote:
Originally Posted by SAMM3Y View Post
Quote:
Originally Posted by M43S7RO View Post
Got the same code, no dash light. Changed the thermostat temp sensor and thermostat and noted that the car warms noticeably faster.

Dunno how long I drove with either a bad thermostat or sensor as it was a few yrs of ownership before I ran into the code while loading a tune.

Doesnt make sense that that BMW wouldn't have this trip the dash light.
Yah I've been thinking about this. The dash shows oil temp not coolant but anything connected via CAN does show coolant temperature too and I've never noticed a deviation but like Mark I've seen this code before too only when I have a laptop connected for flash. Thermistors typically don't go out of range a little and they typically only fail when they are subjected to extreme elements like freezing then hot, maybe the m3 only alarms when oil temps go crazy? Seems weird if the coolant temp sensor goes out of range and doesn't throw a CEL.
I should add that I have the, whatever you call it, electric steering wheel that shows oil and coolant temps and both, from what I've noticed when I've checked have always been within range. You'd think it would through a CEL.

To add to this same thing is happening with the O2 sensor. Code reader shows a failure but nothing on the dash. I just attribute it to the active autowerks tune?

-Mark
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