The Motor Electronics Component System (MECS) consists of:
Inverter Cooler (in front of A/C condenser and radiator)
Hoses - carries the coolant
Reservoir - holds the coolant
MECS Pump - circulates the coolant
DC to DC Inverter - uses 300V to supply 12V and recharge the 12V battery
eCTV - uses the MECS to cool the transmission

Logically, to fix an overheat, I checked and replaced the MECS Pump. While the pump is removed, back flush and forward flush the cooler, inverter and reservoir. Drain the system and add fresh coolant with a wetting agent that improves heat transfer. After eliminating all the less expensive items, replace the DC to DC Inverter. It's easier than replacing an alternator, but performs the same function (on a hybrid.) Be sure to disable the 300V battery and disconnect the 12V battery ground before performing the replacement. People have suggested using a vacuum bleed, but it doesn't work as the system is self bleeding. The code has nothing to do with the electronics on top of the transmission. I got a used inverter from a wrecking yard on eBay. Improved my 12V battery voltage (from 13.1V to 13.5V), but didn't correct the MECS overheat indication. Next item to replace is the DY1144 temperature sensor mounted between the two coolant lines on the eCVT.


The inverter is located behind the two coolant reservoirs.
Update: Please note:
The MECS is very simple and only contains the components shown above, but also cools the eCVT. The HV Battery have nothing to do with the MECS.
The eCVT doesn't have a transmission fluid cooler and uses the MECS for cooling.
The High Voltage Battery located in the rear of the vehicle is cooled by it's own heater/air conditioning evaporator, much like the cabin heater/air conditioner. There are two fans located at the rear of the battery to force cooling air through them. You can hear them operating quietly when the vehicle is stopped. If one of the fans fails, the other will go into high mode and you will hear a fan roar coming from the rear of the vehicle. MPG will suffer severely until the fan is replaced. You won't get any codes unless you have an all modules reader.

 

2011 Ford Escape/Mercury Mariner Hybrid MECS system including part numbers

This video may help anyone who is interested in such things. One important thing to note is that the MECS pump itself runs off of 12V (not high voltage!) and it should run as long as the 12V system is good. It is very similar, in fact, to the "after-run cooling pump" system on turbocharged Audis from the 1980s. On those cars, after a long drive when the engine was switched off, the turbo and exhaust manifold would heat soak, which could cause the oil in the turbocharger to "cook." So Audi designed a small pump system that looks almost exactly like the MECS pump on these cars to circulate coolant through the turbocharger and cool it down. Some owners learned about its existence after the temperature sensor that switched it on failed and their turbochargers "cooked" anyway.

"The vehicle uses a pump driven cooling system (referred to as the Motor Electronics Cooling System (MECS)) to transfer heat generated by the eCVT and the Hybrid Electric Vehicle (HEV) battery pack to the atmosphere. The system uses a coolant-to-air radiator design.The MECS pump is an electric pump that runs any time the ignition is in the ON position. Unlike traditional cooling systems, there is no thermostat in the MECS , so coolant flow should be continuous and considerably less than traditional powertrain cooling systems.

The flow direction is from the degas bottle and DC/DC converter to the MECS pump through the eCVT , then through the MECS radiator from the LH to RH side of the vehicle back to the degas bottle.

The MECS cooling pump will make an audible noise if it is running and a slight vibration may be felt. Flow can be verified by visually inspecting for coolant flow into the degas bottle. Only a portion of the coolant flow is diverted to the degas bottle via the "T" in the coolant outlet hose."

 

That's a direct quote from the 2011 Ford Workshop manual for the Escape, Mariner, Escape Hybrid and Mariner Hybrid. I didn't write it, and they're being a little vague. Now we know why people get confused, including the Ford techs.

 

I found a picture of a AM6Z-7000-A transmission and it does appear to have two coolant ports to the front. There doesn't appear to be a transmission oil cooler. From what I can see, it appears the hoses from the engine cooling system may be connected there. I'll look in the morning to see where they are and where they go. I used to write technical manuals for a living, so I know they aren't always accurate. Only as good as the person writing them. More to come.

 

It's a pain in the butt. When I got this car I knew nothing about it and sometimes reading the service manual I feel like I know less. And that's from a 2011! You'd think by that point they would have edited those kinds of strange things out. So we all have to work together in good faith because even the factory workshop manuals can be misleading. People get confused, they insist: "It's right there in the manual!" Except the manual is wrong!

 

I have 2007, 2009, and 2010 Ford Escape Hybrids. I feel your pain. They fail, but don't give you a code. Then when you finally get a code and read it before turning the car off, the code is nebulous and no one seems to really know what the code means. hv fan failed, no dtc code or other indication, throttle body failed, engine stopped, took forever to finally read a code, now the Maintenance Wrench, which I could ignore, but I don't want to lose MPG. Code was for inverter, but everyone thinks it's something else. I like the way you think, we have to pull together.

 

Top schematic is a good picture. Hose 6 takes coolant from the bottom of the inverter cooler (front radiator) to the inlet of the eCVT. Hose 5 takes coolant from the outlet of the eCVT to the inlet of the MECS pump. The pump then sends the coolant to the reservoir and Inverter.

 

I think you have 5 and 6 reversed but yes, that's where they go on my car.

 

You were right. I corrected it. Wouldn't it be funny if we're all getting the error code because the lines were reversed. I doubt that the eCVT cares which way the coolant flows as long as it flows. f've ordered the temp sensor and am going to connect it uninstalled so that it just measures ambient to see if that corrects the error code. Since there is nothing short of $1000 that I could do to correct an overheating eCVT. I'll just drive it til it fails if the sensor fixes the problem.