My 2008 FEH has been running great and saving me fuel a plenty over the summer (40-50mpg) but now is behaving weirdly. Anyone know what may me preventing my truck from going into electric drive mode in the colder temps?

Details:
- When outside temps are below 20 degrees F (-7 C) my ICE runs constantly
- Coolant is warmed and at operating temps
- Battery pack is showing full charge
- Climate control settings on auto with econo mode selected
- I've blocked the radiator ~75%


The only strange thing I notice is battery temps are showing slightly above freezing (35-40 degree F). Does it have to warm up further?

Thanks for any advice.

 

One missing piece of information is how long you are running the vehicle before expecting it to be able to enter EV mode. My 2006 (RIP) was definitely reluctant to enter EV mode in extreme cold, but would (albeit only for brief periods) after sufficient warm up/driving time.

One other point is that I believe using auto mode on the climate controls also works a bit against better mileage in very cold weather. It will start giving you cabin heat as soon as the engine is warm enough to steal some. It's better to wait until the engine is warm enough to actually have waste heat. It's a question of comfort vs. mileage, though not nearly as significant as the similar tradeoff with A/C in Summer.

 

Yes, under certain operating circumstances it won't go into ev mode. Such as cold weather and light usage combining to prevent the catalytic converter and/or hybrid battery from getting warm enough. In my case, starting cold and then driving down a long descent, like 8 miles, it won't go into ev mode in the winter, but will in the summer.

 

Thanks for the input.

It will not go into EV mode after a 30-45 minute drive on the freeway.

I've done some more monitoring and going to presume it is battery temp related. Today my battery pack was able to get to almost room temp (60 degrees) and EV mode worked fine. Below 45 degrees it doesn't like it.

The only other thing I'll check is the flapper door in the rear air vent to make sure it's not remaining open (i.e. cold air on battery)

 

I can see it refusing to go into ev mode after a 30-45 minute highway drive if it was extremely cold, like minus 20 degrees. But at 45 degrees it should be more willing to go into ev mode.

 

I am not by any means an expert but feeling as though my 06 MMH was going into EV mode less than expected - particularly when it was cold - I took it in and they replaced the thermostat. The tech I believe said something about the thermostat being stuck open and commented that I must have had very little heat available in the vehicle.

I was blown away at how much more I go into EV mode now - I see very little difference between summer and winter driving ev engagement after the repair. It seems to stay in ev mode for less time in the cold but I feel like it engages almost as quickly as in warm weather. I think after driving it for six years I maybe missed a slow decline in ev engagement and I use my seat heater almost continuously in Indiana winter which I think helped compensate much for the cabin heat. That and I travel fairly short distances so really never expected to cabin heat to be at full capacity. But the tech wasn't kidding - when I got it back all of the sudden do I have heat and quickly!

 

First generation FEH software generally requires a hybrid battery temperature of equal to or greater than 45f, cylinder head temperature of 184f and water temperature of 155f before EV is allowed. The engine block heater option also connected to the rear hybrid battery heater so one could pre-heat their important items prior to starting it up in the AM. Mine went kaput and their no longer any produced to replace it.