With the cold weather (below zero F) the last couple of days, my '05 is acting weird again.
OK, here's what's happening, FEH fully warmed up (after around 20 miles at highway speeds)

CHT > 220
SOC >53
Tav (avg. HV battery temp) >60

As I pull up to a light in town and it goes into EV mode just like I'd expect it to. But the heater stops putting out heat - I'm pretty sure this is probably the cabin heater pump is bad. (forgot to replace it this past summer.) So, I try setting the heater controls into the 'Red Zone' (heater/defroster or defroster) which should force the gas engine to start back up. Wouldn't start back up no matter what. I finally set the heater controls to 'OFF' to get the fan to stop blowing frigid air on my feet. I'm pretty sure the heater control switch is working correctly since when I put it to 'Defroster' it does correctly direct the air flow to the defroster.
This same thing happened last winter and if I remember correctly, disconnecting the 12 volt battery for a while 'rebooted' the computer and things started acting right again. In slightly warmer (above 20F) earlier this week everything acted perfectly normally.
Any ideas what I might check? I have a scangauge so I could check any FEH parameters if needed.

 

By design the A/C pump doesn't run in sub freezing temps, there's nothing that would start the engine other than the gas pedal.

 

With the engine cold, I would open the radiator cap and make sure that coolant is filled to the top of the radiator. I would also use a hygrometer or refractor to check adequacy of antifreeze for those temperatures to make sure that the coolant is not freezing up in your block. Next, I would replace the thermostat even though your scanner is showing that engine temperature is fine. Thermostats are relatively cheap and easy to replace but fix most of the heating issues.

 

Fix the cabin heater pump and it will probably be back to normal. Thermostat wasn't cheap; Ford dealer charged $288 to replace mine.

 

I do most of maintenance work myself. The last thermostat I replaced was under $15 and about 45 minutes to replace.

 

Just got the thermostat replaced earlier this winter and have the cabin heater pump on order. I will report back after I get that changed out.

 

The FEH thermostat is NOT a $15 part and its replacement is not as easy as on a lot of other vehicles.

 

I got the cabin heater pump I had ordered. I'm getting that replaced on Tuesday. Too cold and/or wet to be laying in the driveway playing with antifreeze lately. I'll be glad to get/keep the cabin heat flowing when in EV mode.

Now with slightly warmer temps (around 25-30F today) I noticed that I can forced the ICE to turn on/stay on by flipping the heater control into the 'red zone'. It would not do that for anything a few days ago when it was at or below zero F outside. Anyone ever had that behavior?

 

Finally got the pump replaced today. Only cost 1/2 hour labor at the local mechanics shop. Once everything got warm enough on the way home (took a while as it's still only just above zero F today) to get into EV mode, the heat kept on a comin'. Boy did that feel good. At least now my toes won't freeze sitting at stop lights.