The oil pressure sending unit is at the rear of the engine driver side behind the doghouse. Remove doghouse, disconnect the electrical plug from the sending unit. Turn key on. Do not start. Guage should go to full scale. Then to zero with no connection to sending unit. If it goes back up to full scale (pegs) the problem is in the dash, that is the total instrument cluster. A new cluster is about 450.00. There are third parties where you can send the cluster and they will repair. If the gauge goes to zero and then stays there. The problem is the sending unit, available at O'Rielly's or the Zone for about 65.00. There is a problem with the oil pump in these units, I am on my second oil pump on my 2005 with about 475,000 on it. This time putting m365 pump in (high volume, high pressure), it seems that the pump can suck the relief valve down, especially if there is any gunk buildup on the suction screen, and then not build the pressure it should. Pressure tapers off as it warms up , or not at all if the relief is stuck in bypass mode.
sent from S4 using EO