I was getting a P0171 code along with terrible fuel mileage and a barely functioning EV drive. I replaced the PCV valve, PCV hose, intake manifold gaskets, Throttle body gasket, fuel injector O-rings, air filter, fuel filter, O2 sensors, mass airflow sensor, fuel pressure regulator and for the grand finale the battery pack fan assembly. Now the code is clear, EV mode is working like new but a very weird thing is happening now. When I check my MPG, by actual measurement when not using the a/c, it is 26 to 28. Doing the same test with the a/c on the MPG is cut in half to 14 or 15. There is no other sign of a problem; it runs great and no trouble light or codes. Seems impossible to me but the test has been repeated many times. The only things I haven’t replaced yet are plugs and ignition coils which are on order. Any thoughts would be appreciated.

 

Makes no sense;
Only things I can think of would be the HV blend door? Maybe it's stuck, so it's trying harder to cool it off than necessary.

Front & rear air filters?

Hows the cabin AC? I just went thru replacing that complete underhood system; AC at the vents was only 'cool'; when I put a thermometer up it was like 50-60F; a little cooler while driving.
Started with just the AC compressor control valve; that got me

 

I replaced the the a/c compressor last year and it is working fantastic now. The blend door is opening and closing perfectly and I did replace the filter. Thanks for the input.

 

IDK???

How are you noticing the loss? Actual pump & calculator, or on board computer, SG, ???

 

Actual pump measurements.

 

Looks like it is running a bad air/fuel mixture under load,. You could also have bad catalytic converters from running rich. Technician could diagnose properly.

 

Or the A/C is simply making the gas engine run more.

Totally reasonable numbers for stop & go.
Low for primarily highway. Unless you drive 85-90 mph.