P0A7C criteria PCM parameter / wrench light?

[wr400f250]

Checking in again. Just replaced engine and mecs coolant at 191K miles. Also took the time to replace MECS pump. Old pump seems to be working fine.

I spent all day tinkering with the cooling system, flushing it with distilled water, trying to find a blockage. While doing this, I noticed that both pumps, while functioning correctly, were unable to circulate the water through the system. I unplugged every hose trying to flush out anu blockage, and make sure the coolant paths are clear.

I began bleeding the system with pure distilled water. In doing so, I wasted a lot of water trying to diagnose the system. I found out, following the service manual instructions left way too much air in the system. The pump was barely drizzling any coolant, and the system was being vapor locked.

After draining completely and filling with new coolant, I took my sweet time purging the system of air. It took A LOT of ignition cycles, opening the bleeder screw, etc, and finally I could hear the pump sound distinctly different. Before, it sounded like it was freewheeling. Now, it's definitely circulating coolant.

My suggestion, take your sweet time bleeding the system. The pump is a centrifugal pump, meaning it is incapable of moving just air alone.

Took the car for a very long test drive at 80mph+ last night and MECS coolant reached about 115F. Generator inverter was the hottest thing at 230F, but that was peak at a long uphill. I'll know for sure next week, my sister will be borrowing the car, driving 6 hours through the Mojave Desert into Arizona. I'll keep everyone posted.

[wr400f250]

Just took the Fusion to work and back. 100F outside temperature, A/C on full with two people in the car. Took the back highway from San Bernardino, CA to Crestline, CA (about 3700ft elevation gain in 12 miles) and back down to Hesperia. Total drive is about an hour, 50-60mph average. Temp dropped to about 85F at the top. Here are what the vehicle temperatures topped out at, mostly very brief:

Motor/Electronics coolant: 127F (excellent)
Generator Inverter Phase: 220F
Motor Inverter Phase: 170F
Generator Coil: 230F
Motor Coil: 220F
Engine Temp: 202F (nice)

I'm not sure what the upper limits are, but these seem very reasonable for what I was doing MECS topping out at 30ish degrees above ambient temperature is outstanding. Phase temperatures are the primary heat sources for the MECS coolant, and these were peak temps with some pretty spirited driving by my brother. I believe the coil temps are inside the transaxle itself and not directly cooled by the MECS coolant, as they stayed pretty consistent.

Overall, I believe I solved the issue. The absolute test will be in a couple days, when my sister borrows the car for an Arizona trip. If the wrench doesn't come on at all, then the issue on my car is 100% solved.

To summarize what I did:
- Drain coolant
- Thoroughly flush system with distilled water
- Add fresh coolant (Zerex G05 in my case)
- Bleed the system for hours until I could hear the pump loading up (pumping liquid instead of air).

[samster2.0]

Here's an update on what I'm looking at right now...
I'm just trying to track what PID is triggering that wrench light, in hopes of it shedding some light on the root cause. Because outside temps are heating up, and because I'm driving more frequently, my wrench light is coming on more often - gradually.

I may be onto something with watching the "DCDC" module and the PID "MotCoolTemp". A drive home this evening, on the interstate, in TX (91 degrees outside) - I'm driving 80mph on the interstate for at least 45 min. When "MotCoolTemp" hit 129 for about a minute, then the wrench light came up.

Shutting down the car and restarting cleared it (as it usually does). Got back to driving and got that "MotCoolTemp" back up to the same 129, and even though it fluctuated between 129 and 127, after about a minute the wrench came back.

As soon as I got home, it was reading 131. I popped the hood, opened the top of the coolant reservoir for the electronics, stuck my finger in it - and yeah, it felt about 120-130 degrees (like a warm shower water temp). I can never actually see that coolant circulating, but I can hear the pump running, and the coolant was definitely that temperature. The whole thing with this wrench light is stupid - Like why do I care if my coolant is warm? Does it warrant sending an ominous warning to the driver to take their vehicle in for service? UGH.

If anyone else with a 2012-ish FFH is watching their PIDs, let me know what your DCDC / MotCoolTemps are when your wrench light triggers?

[samster2.0]

Overall, I believe I solved the issue. The absolute test will be in a couple days, when my sister borrows the car for an Arizona trip. If the wrench doesn't come on at all, then the issue on my car is 100% solved.

To summarize what I did:
- Drain coolant
- Thoroughly flush system with distilled water
- Add fresh coolant (Zerex G05 in my case)
- Bleed the system for hours until I could hear the pump loading up (pumping liquid instead of air).

@wrf400f250: Definitely report back, please! I am thinking that a larger, more powerful aftermarket coolant pump (like one from Jeg's or Summit) might be the way to go - just to move more coolant faster. That, or (god forbid) some super-fantastic coolant additive. I'm still using the stock Ford "Specialty Orange" coolant mix, although the dealer flushed it and replaced it a few years back, and I've kept it topped off.

Its frustrating that we have to go through all this because of *warm* coolant.

[wr400f250]

I had been watching the DCDC converter temp (MotCoolTemp) beforehand as well, but forgot to watch it on that short trip.

I doubt any temperature below 135F in the MECS system would cause an overheat warning. Reason being, Fords (as well as many other cars) are tested within the extremes of real world climate. Where I live, temperatures above 120F are not uncommon, and places like Laughlin, NV or Death Valley often reach temperatures of 125F - 130F. The design of the MECS system is such that it will never cool below ambient temperature, so that has to be taken into account when designing the system.

The DCDC converter is the first stop for the coolant after the radiator, so it's also the coldest. I would expect it to be lower than the MECS coolant temperature (measured at the transaxle). If it's reading higher than that, then you would have a major flow issue (or lack of flow entirely). Something to think about while looking at your PIDs.

Coolant flows in this direction (from the pump):
1. pump outlet > transaxle > MECS radiator > DCDC Converter > pump inlet

[wr400f250]

Just got a phone call, wrench is back on. This rules out the coolant pump as well as coolant/circulation. There is something else going on here.

Primary suspects now are DCDC converter, coil temperatures and phase temperatures

Will post updates in a few days when I get the car back.

[wr400f250]

Just read through my service manual (which isn't nearly as much help as you would think). I can confirm that the DCDC Converter has an upper limit of 176F measured at MotCoolTemp, at which point it will restrict output to a maximum of 100 amps (145 is normal maximum). I believe this rules out the DCDC converter as a suspect.

My next steps when I get the car back are as follows:
- Check the system for air again
- Find a way to measure temperatures at each inlet/outlet pipe
- Find a way to visualize flow, possibly replace the tube between the MECS pump and transaxle with a clear one.
- Figure out how to measure transaxle fluid temperature, maybe replace transaxle fluid.

If coil temperatures are the issue, then we may need to add a transaxle cooler, or even add a fan to the cooling fins on the transaxle.

If anyone wants to replace transaxle fluid before I get to mine, it's absurdly easy. There's a drain plug at the bottom, drain all the fluid. Then, there's a fill plug on the side of the transaxle. Simply fill to the bottom of the fill plug. Transmission fluid per service manual is Mercon LV, XT-10-QLV, 4.28qt

[wr400f250]

Got the car back and read codes. Still MECS overheat, but I also have P0A3E generator inverter overheat. This was intriguing, because it means either the system isn't bled, or the inverter is bad. Obviously, I'd like to make sure the system is bled before I condemn the car!

So here's the fun part, I found a second bleeder screw. It's located directly at the top of the inverter, next to the outlet for the DEGAS bottle. It's a very short screw, 12mm bolt head. A 3/8 drive socket was perfect, and you'll have to disconnect the two electrical connectors at the top to reach it. I dropped the bolt, don't do that (I'm still looking for it...)

[wr400f250]

Found the bleeder screw in front of the sway bar, and dropped it again, found wedged between the wire harness and firewall just under the brake reservoir. A magnet is your friend here.

Bled the system again, air came out of the top bleeder. Thanks to Coronavirus, I'm free this week so now I'm going to make a trip to AZ. I'll report back on how it goes.

Sitting in the driveway, PIDs look promising. G_PHTMP and M_PHTMP are staying within a few degrees of each other with the engine running. After shutdown, they almost instantly match each other (this was not the case before). MotCoolTemp and MECT are a complete match, not surprising considering I'm sitting in the driveway.

My wife is coming with me, so I'll be able to monitor PIDs for the duration. Wish me luck!

[wr400f250]

Just got back from Arizona. On the way there, the car made it about 3 hours with zero issues, about 104F ambient temperature, 75mph average. Past the state line, I got the wrench again. Had two stop safely now events on large uphill climbs, where ambient temperatures reached 108F.

The codes I got were MECS overheat, and Generator Inverter overheat. I learned a few things this trip:
1. MECT and MotCoolTemp absolutely share the same sensor, located on the inverter output.
2. GCLTEMP and MCLTEMP are the coils inside the transaxle, physically cooled by the transmission fluid.
3. G_PHTMP and M_PHTMP are cooled by the MECS. G_PHTMP controls GCLTEMP and M_PHTMP controls MCLTEMP
4. The issue (with my car) is definitely not the MECS coolant temperature. Highest I saw was 140F, under the most extreme conditions.

Here were roughly average temps on the way there at 75mph, about 108F ambient air:
GCLTEMP - 273F
MCLTEMP - 228F
MECT/MotCoolTemp - 138F
G_PHTMP - 246F (culprit of SSN events and MECS overheat code)
M_PHTMP - 158F

Changed transmission fluid (will throw in the procedure after posting this, stupidly easy) in Arizona and drove back home. Here are the results:
Ambient air, peaked at 118F, average about 111F. Average speed, 70MPH (could not maintain on hills without SSN events)
GCLTEMP - 259F (huge improvement)
MCLTEMP - 230F
MECT - 142
G_PHTMP - 248 average
M_PHTMP - 163 average

The increased ambient air temp had a direct effect on operating temps, as expected, and contributed to a total of six SSN events on hills. A/C was amazing though. Even with the increased temperatures, changing the transmission fluid made a huge difference in coil temperatures, and I very much recommend doing it.

My conclusion so far is this:
1. MECS coolant temperature is absolutely not the culprit of anything, nor is transaxle temperatures (though I would like to add an oil cooler)
2. MECS coolant flow is still a suspect, possibly air is entering the system (I suspect the bleeder screw on DCDC), which explains why I made it 3 hours at 75mph with zero issues.
3. The only possible thing left for me to check is the inverter itself. This will require disassembling the high voltage inverter assemblies, which should not be attempted unless you've been trained and know what you're doing. My #1 suspect here is the dielectric grease mating the generator inverter to the coolant heat sink. The inverter fluctuates a LOT while driving, which means a lot of heat cycles for the mating surface to expand and contract. I may not be able to reach it without removing the transaxle, so it might be a while before I have an update on that.