Originally Posted by MRod
When the vehicle idles, the oil pressure drops to zero. The check gauges light also is coming on and so is the check engine light. Anyone have any idea what might be causing this. I've checked the oil and its fine.
Could be a bad oil pump, but most likely it's going to be a bad oil pressure sending unit. For the 4.2L I-6 engine, the oil pressure sending unit is just right next to the oil filter, the only tool you have to purchase is the long 1 1/16 inch socket, which is made for installing/removing oil pressure sending unit.
Without it, it would be difficult to torque it down. I guess that is the main reason for the thing to come loose in most Envoy's and Trailblazers. The oil pressure sending unit part # 12611588, look into the oil filter area and change the sender unit. Just disconnect the electrical connector and your good to replace the Sending unit.
Good luck and keep us posted and to be safe. Have a mechanical oil pressure gauge check the actual oil pressure.
Be careful about assuming that your oil pressure gauge is showing you any information about the health of your engine. All that it really tells you is that your oil pressure is something above a specified level (a value I couldn't find in the manual but the minimum acceptable oil pressure is specified as 12 psi so it is probably a value below 12 psi)
GM's description is that the oil pressure is monitored by a 3-way switch, It will signal the PCM @ 0psi, 40psi, & 80psi and all readings in between are calculations made by the PCM using this information and other inputs based on a pre-determined set of conditions programed into the PCM