Hi guys. Has anyone found a cause of this issue or specific solution? My 09 with 171k miles started having this issue on long drives in the past few months. I actually towed a U-Haul trailer from Austin to Houston two weekends ago. The vehicle did great on the drive, but the light came on within the first thirty minutes. I had done a full coolant flush (both sides) at the Ford dealership right before the trip hoping that's what it needed. I've also been using torque pro with the additional PIDs to monitor as many temps as I can, but the issue is I don't know what normal operating temperature is for any of the signals really. We're also in the middle of a pretty hot Summer, so I'm hoping this issue will calm down as the weather cools off.

I wonder if there's some additional temperature sensor on these vehicles that none of us are reading with our scanners.

If anyone has found a specific issue, please share. We're looking at purchasing a small pop-up camper (lighter than the U-Haul we towed) for camping a couple times per month, but I want to make sure I'm not risking something catastrophically failing on us while I'm driving my family down the road. Hope we can figure this out, but I'll probably just keep driving it until there's an actual failure. Good luck out there!

 

Try this.

Could simply be that you're pushing it too hard by towing, thus raising the MECS coolant temperature to the point the DTC is tripped. FEH has a tow limit of 1000#, and it's really easy to hit that. Furthermore, it has a maximum frontal area limitation of 24 sq-ft.

 

I really appreciate the document you attached! Yeah, I get what you're saying about towing, but the issue is (and was) happening to me prior to ever towing anything. It happens just when I go on long drives, same as you guys. I don't doubt that towing is putting additional stress on the system, as that's obviously what towing does, but that is not the root cause of this issue. Regarding the amount I'm towing, I know it exceeds the amount recommended by Ford, but I've actually read on other forums about a few guys with FEHs towing much more than I am with no issues. The theory is that Ford set the number low due to reverse on the FEH. In reverse, these vehicles can only drive the wheels using the electric motor, meaning you have less power available in reverse. If I can find the forum post, I'll link it here later. Again though, I do appreciate your input!

 

Hi guys. If we are more precise to understand the problem, then it is not that the cooled liquid exceeds the temperature threshold. And the fact that the windings of electric motors heats up more than the calculated one. In theory, it is necessary to cool the oil in the box additionally, since the windings are cooled with oil. While I see an option to take from the drain hole, through the fitting with a hose to the oil pump and drive it through an additional radiator and return it to the filler hole. But I haven't implemented it yet.

 

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.

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 and corrected the MECS overheat indication.


The inverter is located behind the two coolant reservoirs.

 

i think james is right i have an 09 and when I tow my 6x10 box trailer i sometimes get the code/wrench light. I monitor trans/gen/motor with a snapon scanner and temps on all 3 can approach 200 without setting a code. I dont see anywhere on this scanner to monitor dc/dc converter. Is forscan able to monitor it?

 

The Pin Out diagnostic document is an excellent resource, thanks to the poster. Now that I've gone through the system and eliminated everything that it isn't, I believe my problem is a bad PCM. I soldered a 10K ohm resistor across the temp sensor, voltage dropped to 1.5V and got a failed sensor error code. I removed the resistor and replaced the sensor, quick $7 fix. Didn't work. So I soldered a 4.7K ohm resistor in series at the connector. Voltage rose to 2.6V which should have kept the temperature well into the cooler operating range. Still got the same code, overheating, but there is no way it could get that signal, so either I have an intermittent open circuit or short, or the 5V reference in the PCM is bad. I have since noticed that my fuel gauge when full shows above full (normal) then occasionally shows just above 3/4 tank, then goes back to full sometimes. I'm now getting random failure codes like EGR and O2 sensor.

This all leads me to believe that the PCM is failing internally and is losing all voltage reference.

 

The coolant sensor on the transmission will really only tell you if there is a bad pump. The transmission would have to be going bad and making a lot of noise to overheat the coolant. It's frustrating that if the sensor were telling you the transmission is overheating, the fix is to replace a $7,000 transmission, not something that any of us are going to do. Get a new sensor, connect it and let it dangle uninstalled. If you get an overheat indication, then the PCM or wiring is bad.

 

Im not sure which temp sensor sets the code. Doing what you described with one sensor will not tell you pcm/wiring is bad if there is another one of the temp sensors that can set the code. To be able to figure this out 100% we need to know the software strategy and unfortunately i cant find it anywhere online or in the factory service manuals that i have 😔

 

plumbing in a trans cooler with a 12v diesel fuel pump to see if it helps while towing trailer