the ref 1 and ref2 circuits are separate circuits. So if the fault code is for ref1, forget about ref 2...at least for now.



when you disconnected every 5volt ref 1 connector from the list I posted and checked for 5volts at one sensor. did the voltage drop out at all when the other connectors were plugged back in one at a time?

Found issue in voltage upon connection of the EOP. I sent you a PM with the details

Thanks

Joe

Update
 

Well after about 7 weeks of dealing with this craziness we may have solved the problem. A big thanks goes out to Mike (aka The Cleaner) and Tech2 for their help.

Here's the run down kept receiving a P0641 DTC which indicated an issue with the 5 volt system. And also it put the engine in "Reduced Power Mode" Every check kept leading back to the Engine Oil Pressure Sending Unit. I replaced the sending unit on 5 different occasions 3 from PepBoys 1 from AutoZone (complete piece of Crap snapped while installing) giant PITA to install without taking off the Intake.

Replaced the wiring connection no change still kept tripping the P0641 DTC. After doing some additional testing I decided to make a new wiring harness (found out the hard way) All three wires lead directly back to the ECM connector (in all the schematics I reviewed it showed only 2 wires the gray & black ones going back to ECM) it was assumed that the tan/white went to ground. After a phone call it was found that the wire does go back to ground but through the ECM.

Decided to go with 5th sending unit (OEM) BINGO

SO my Public Service Announcement use only OEM EOP's or you'll regret it.


Joe

when new parts are bad out of the box; it throws a wrench into the diagnostic process. bet it was hard to convince yourself to buy that 5th sensor.


thanks for posting the fix.

Words cannot express what was going through my mind when I decided to go with the 5th sending unit. With everything else that I went through with various testing and procedures it was a good learning experience though

It still would have been nice for the first one or three to work

Thanks again for all of your assistance.

Now onto the problem with my 04 Tahoe will post that shortly

i know this is a couple years old, but my 08 suburban came up with the code reduced engine power, service stabilitrak, and traction control off. I replaced the Throttle body thinking that was it from other research i did about the problem. It wont start now, just keeps turning over but will not run. I have replace my Oil Sender Unit 3 times within the last year myself. My oil pressure seemed good when it was running, but didnt know if you had any other info. I took it to a shop yesterday and they said it was a short and unplugged the Oil Sender Unit and said it worked fine, but they plugged it back and and i tried to start it today and it wouldnt. I unplugged it and it still wont start. I have the PO416 code as well, and thats the only code i have. Any help would be greatly appreciated.