Chrysler 300C oil pressure warning

I am constantly getting a dashboard light coming on along with a warning chime suggesting that oil pressure is low. I have tested the oil pressure and it reads OK. Taking advise from Chrysler at Chelmsford I have changed the oil level and temperature sender in the sump?? and this made no difference. There is no external pressure sender but there is an internal one which has also been changed. Oil level is perfect (just below the max mark) and pressure Ok so I am now stumped as to why the alarm is still sounding!