Oil Pressure sensor is ABS??

Or does it not make a big difference if I'm only putting around at 2000' typically? Even with small changes in barometric pressure, I guess it's only a couple of psi difference??

OK I now realize this is the 4th gen sensor part no. 456180. I've read a few threads here discussing it's range of 0.75 to 10.75 bar but no one seems to discuss that it's measuring absolute pressure meaning it's referenced to 0 bar absolute (vacuum). So with engine off and atmospheric conditions of 1 bar, the sensor will indicate an oil pressure of 1 bar (14.7psia). On the ground engine running, the indicated pressure will be 1 bar (14.7 psia) higher than actual. I just don't get using an absolute pressure sensor for indication of oil pressure.

The installation manual does state that the oil pressure sensor is absolute pressure, and that there will be about a .2 bar (3 PSI) indication at zero pressure, depending on the elevation and ambient pressure.  What is not explained is why that deviation is not closer to 1 bar (14.7 PSI). The answer lies in the scaling of the sensor. The sensor is scaled at 0-20 MA = 0-10 bar respectively.  However, most displays are (or can be) scaled for 4-20 MA = 0-10 bar respectively. If you look at the output graph for the oil pressure sensor (in the 912 installation manual) the output reaches 4 MA at about 12 PSI, which your display is calibrated to read as zero. The difference in 12 and 14.7 is 2.7. So at sea level and standard pressure you would see 2.7 PSI at 0 PSI of oil pressure, thus the approximately 3 PSI error as stated in the installation manual.  Don’t change your sensor, it will be fine with your new engine monitor.  

Thanks Jeff. That's a good explanation. I'm not sure how my current GRT EIS is scaled but I know the new EIS I'm considering can be scaled however I like. Do you have an opinion on why they chose an absolute pressure sensor over a gage pressure sensor??

Norman, 
Using an absolute pressure sender is simply more accurate for aircraft.  Once the engine is producing oil pressure it operates much like a sealed system, with the effect of ambient pressure being minor. Having a gauge pressure sender referencing ambient will produce much wider fluctuations with altitude and pressure changes.  There are also pressure changes within the cowl that would affect a gauge pressure sender.