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2.0GHz, 2.3GHz, or 2.6GHz quad-core Intel Core i7 processor (Turbo Boost up to 3.8GHz) with 6MB shared L3 cache.

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Left fan constantly runs full speed - no load, no overheat

My late 2013 MacBook Pro took a Coke spill right into the keyboard about a year or so ago. The machine returned to gook working order after a while (despite keys that can be somewhat sticky from time to time). Recently, however, the left fan has begun running at full speed constantly. SMCFanControl right now reports it at 6846, and this doesn't seem to fluctuate at all. The fan begins this behavior immediately after bootup, even before the Apple logo appears. This has happened once or twice in the past, but after a short while the fan returned to normal.

The system is not under any CPU load whatsoever, and this happens with the laptop on a hard and flat surface. The left fan seems to be the only one affected.

I ordered and installed a brand new left fan, just to rule out an issue with the fan itself. Same behavior - full speed ahead.

The last 3 of my serial are D59.

I would suspect that this could be related to the sensor(s) being compromised in the spill, but I don't know where to look to check them, clean them, or anything else.

Can anybody give me any pointers or next steps?

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Give 820 number of your board, which is written on logic board so we can find the proper ASD test for your laptop. A sensor has failed which is causing this behavior.


Where would I find the number on the logic board? I just want to know where I'm looking when I take it apart again. Thanks!


See the picture above.

To the left from the battery connector, you have a small rectangular sticker with white writing. That's your Logic Board's S/N. But, the unit's S/N should suffice. Written your Mac's bottomless. Starts with "C02".

Either way.

It sounds like a temperatur sensor in your top case is dying, and making your fan go nuts. Well known issue amongst technicians.

I can't remember at this time (3:40 am where i am), if the 2012 Retina's can run AST2, but i'll check my own tomorrow, and if it works, i'll give you a heads up, and we can run it together at some point. That should pinpoint which sensor is making a fuss.


You have most likely damaged a temp sensor near the cooling fins of the heat sinks.

The easiest way to see what the issues might be is to have an ASD test run on it.

Im willing to bet 99% its a temp sensor.


S/N from the case bottom is C02MG1W4FD59 but if you happen to actually need the number off the logic board I'll crack it open again and get that. Since I'm using the laptop right now, S/N was by far the easiest to get to.

I will note that running an Apple Diagnostics ("D" at bootup) showed the following, but you guys may be honing into a more precise diagnosis than this…but I'll give this in case it provides more info:

* Reference Code: PPF004

* Additional reference code: PPF003

Thanks to all for the "thus-far" diagnosis!


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You could try running a better app here which can show you the discreet thermal sensors like Temperture Gauge Pro. That would verify which sensor is failing.

From the sounds of it your uppercase sensor is shorted out which is a common issue when you spill liquids into the keyboard.

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OK, Dan - I grabbed a copy of Temperature Gauge Pro and took a look at the output. All of the temperatures are showing green and nothing is above about 109º right now. Is there anything in particular I should focus on in order to find the offending sensor? Average temp is 92º and the CPU is 109º (at this instant). Diagnostics indicate that both fans and temperature sensors appear to be functioning normally.


What are the fans doing? Are they both going at the same RPM?


The left fan is running full speed (7000 RPM at this instant), but the right fan is behaving normally at 2000 as I would expect.


With the temps normal I would suspect the fan is bad. Did you unplug it or damage the connector in some way? If replacing it didn't solve the problem I would suspect the logic board is damaged from the spill or in the process of cleaning it you pulled up one of the load resistors in the fans circuitry.


Thanks for more direction.

The left fan ran at full speed initially, and I replaced it with a brand new one in an attempt to rule out the fan itself. Same result - the left fan still runs full speed. I didn't do any specific cleaning aside from a very light q-tipping slightly moistened with alcohol, so I'm going to err in favor of not having uprooted a resistor (20+ years working inside computers has taught me to be pretty careful). This issue didn't exist for close to a year post-spill, and the machine worked perfectly once it all dried out and everything. The fan issue has only appeared in the past few months, and just suddenly started happening. I am wondering at this point if pulling the logic board and giving it a visual inspection might let me clean something off that helps. It's interesting that the fans were working perfectly until I left the laptop in its bag in the trunk in the Florida sun for a few hours - I wonder if the heat caused some latent Coke to melt/drip again?


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