A good point. Yes, old cats can disintegrate internally clogging passages and leading to overheating of the cat and poor engine performance. Not sure of the parameters but a temp gun aimed at the cat could theoretically tell you if its overheating. What type of heat shields up there? Perhaps stuff some Roxul or a second form of heatshield to see if problem persists. How does engine perform? You could be on to something. Planes rarely crash due to a single problem but a cascading set of problems or multiple issues.

 

If I understand correctly and the generator phase temp is the temperature of the switching electronics in the DC converter module, I would expect to see a rapid drop like you described. That area is subject to a high heat flux (assuming a 95% efficient converter handling 20 hp or so, that's about 700W of heat), semiconductors are small and rely on dumping heat quickly to their environment to not fail, and load in that area would vary rapidly depending on the mode of operation on the eCVT. At highway speeds that motor is also under a lot of load as the transmission is operating in "heretical mode" (where the road-side traction motor acts as a generator and transfers power to the engine-side generator). Under this condition, that motor is operating at maximum speed.

Because of the very low thermal mass of the inverter (it's a few transistors) and high heat flux (meaning that the coolant is in close thermal contact with the semiconductors), you would see a very rapid drop like you described. The car is designed to pull a ton of heat from a very small area, so once that heat is no longer made (e.g letting off the gas) the system can cool the small area very quickly. Scaling in the internal passages would also create behavior like that observed in this thread. Depending on what materials the inverter cooling channels are made from (aluminum?) it may be possible to flush out the inverter with a descaler like citric acid or vinegar (unfortunately, these descalers may also damage the aluminum itself...). There may be descalers designed for aluminum boilers that work without damaging the exhanger.

Don't have this problem myself (~50k mi (unless the creepy salesman rolled it), 2010) just yet.

 

I guess that makes sense if those are low mass components, but I'm sort of trying to nail down if there's a cooling problem...I don't have a good handle on the temp ratings for these things so I have limited ability to judge what of these reported temps are concerning.

I'm late in summing up my trip back but I got plenty more DTC instances (HOT drving - 108ºF ) and still almost no secondary indications of a real problem.
• still no pattern I can see to reported temps. (no one temp threshold that seems to be tripping the light)
• inverter phase showed I think as much as 92ºC which, from other info I can find, isn't overly concerning
• ONE instance of rapid ignition cycling at the top of a climb to Sequoia / King's canyon brought on the traction control error

I had a little bit of battery strangeness the following day (low charge at startup, short drive, high temps and high charge returning to it 40 min later - I will describe that in detail when I'm not under deadline) I think the most relevant part of this was a lack of any warnings, DTCs or lights (even the normal "Electrical Energy OK" message despite clearly offlining the battery, as evidenced by high revving gas engine for reversing (meaning the MG1 was generating traction current rathr than a battery that was reading 68% state of charge). This continues to lead me away from suspecting the battery has any part in the this particular P0A7C message

As for the Catalytic converter - it's aft a bit. It's mostly a flex pipe that runs next to the PTU (there is ZERO shielding). If this is an exhaust heat issue, one would expect to see the TFT rise first.

Since getting back, I just drove up a 6000ft mountain on a sunny mid 70s afternoon with the rpm uparound 3k most of the time without a hint of problem, so it does seem to be more temperature-related than load-related

 

I am not sure what semiconductors Ford used in the inverter, nor where they positioned their temperature sensor. Most high power semiconductors are rated to a junction temperature of 175C. I honestly wouldn't be that concerned by a package temperature of 90C, especially if it was brief.

 

I just bought a 2010 feh in Portland, OR, and drove it back to Tucson, AZ. About 3 hours into the drive I got the wrench light and the p0a7c. My temps also seem to be getting a bit higher than some of you guys, and I also got a ssn and engine shutdown at the end of the trip. I attached screenshots of the temps just after the ssn, but the inverter temps were about 50 degrees higher just before the shutdown and quickly cooled after the engine shutdown and I let off the gas. I also attached a screenshot of the dtc codes from just after the shutdown.

 

I also changed the transmission fluid halfway through the drive, the fluid that came out was black, and looked like it could have been the original fluid with 195k miles on the car. Attached to this post are screenshots of the temps, that I took after every time the wrench light came on.





This is the transmission fluid that came out of the car.

 

Black typically means cooked fluid or old cooked fluid. Did you measure how much came out? Was it underfilled? Did you refill to the "spec" amount? Is degraded or low fluid causing the fault? Any sign of tranny fluid leak under the vehicle? Our 2010 has no dipstick. I changed the fluid once on our 2010 at about 160,000 kmand it did not come out very dark but it probably was the original fluid and I live in a cool climate. I don't recall if Ford even recommends a tranny fluid change but youtube sensation Fordmukoloco (spelling probably wrong) out of chicago certainly recommends them to prevent doom and gloom.

 

I did measure the fluid that came out and it was slightly less than the 5.3 quarts it's supposed to take, but I had fluid come out of the fill plug when I removed it so I don't really think it was under filled, I think some residual fluid just stayed in the transmission. I plan to change the fluid again to get all of the old fluid out, but I don't really expect that to change anything. Getting worried that the transmission is shot. Weird thing is that it doesn't seem to have any issues driving or weird noises. I have a 06 feh as well so I'm going to compare temps on the next long drive I do with that car.

 

An oil analysis might tell you something. Also, wondering if it had the right fluid. If the fluid was totally broken down, it may have accelerated tranny wear and may not have been able to keep temperatures down, especially in a hot climate.

 

An oil analysis might be a good idea, especially if I start seriously considering replacing the trans, but I'm hoping I can avoid that. The trans doesn't have any problems that I can feel or hear. I saved the original fluid so I'm going to inspect it better and run a magnet through it to see how much metal is in it, will report back with that. I'm also planning to long drive with both the '06 and the '10, following each other to see if the temps are close, and if not which ones are off.