IF TOD IS TUNED OFF OR THE TOD CONTROLLER IS UNPLUGGED THE REAR WHELLS WILL ONLY DRIVE THE CAR , NO TOD ACTION AT ALL, FOR THE MOST PART THE TOD WHEN WORKING CORRECTLY WILL DO JUST THAT DRIVE THE REAR WHEELS EVEN WHEN TURNED ON EXCEPT IN A CASE WHERE THE REAR WHEELS START TO LOOSE TRACTION AND THEN POWER IS APPLIED TO THE FRT IN PROPORTION TO THE REAR WHEEL SLIPPAGE, I HAVE MANUAL HUBS ON MY 01 WITH THE TOD AND AHVE SAW NO IMPROVEMENT IN MPG NONE AT ALL, , PROB ON A CHASSIS DYNO RUNNING AT A STEADY SPEED YOU MAY SEE A VERY SMALL CHANGE BECAUSE THE FRT WHEELS WOULD NOT BE TURNING THRU THE FRT AXLES AND THE FRT DIFF, I PUT MANUAL HUBS ON MINE TO SAVE THE FRT DRIVE AXLES , AND THE BOOTS , PERFORMANCE , MPG , NO CHANGE WHAT SOEVER , THE TOD DOES NOT WORK UNLESS IT IS CALLED ON AND THEN ONLY BRIEFLY EXCEPT WHEN IN LOW RANGE.

I replied back and asked why there's seems to be extra drag in these full-time 4wd system -- IF -- the description above is totally accurate. I think a 2WD mode would feel more free-wheeling. And, less drag should help with MPGs.