Oil pressure drops to 0 and triggers alarm in 05 2500 Duramax

[05 Fifth Wheeler]

2005, 2500 LLY. Pressure sensor has been changed twice. Stepper motors in dash have been rebuilt. Engine runs fine. Problem is intermittent. When cold oil pressure is above mid way and drops to just below 1/4 when hot except when problem arises. When the problem arises pressure drops to 0 at low idle. 2 times in 4 years oil pressure dropped to 0 and the alarm stayed on until truck was restarted the next day. The truck was taken to a dealership and there were no codes and the oil pressure system responded normally.
I believe the issue is most likely a wiring issue. Where can I find a wiring diagram for this truck?

 

[2004LB7]

full electrical diagrams here

https://www.gmupfitter.com/wp-content/uploads/2021/05/2005_LD_CKFullSizeElectrical.pdf

 

[TheBac]

On an 05, it could be bad oil pressure stepper motor in cluster.
Double check with mechanical gauge when it happens again.

 

[2004LB7]

On an 05, it could be bad oil pressure stepper motor in cluster.
Double check with mechanical gauge when it happens again.

if it was the steppers the low oil pressure alarm shouldn't be on

 

[TheBac]

Not necessarily. I'd still check it against a mech gauge

 

[08lmm72mm]

OP said steppers were rebuilt

 

[JoshH]

It's either a bad sending unit, wiring issue, or actual low oil pressure. I'm 100% confident it isn't a stepper motor issue. Bad stepper motors don't cause a low oil pressure message to set on the DIC.

 

[2004LB7]

It's either a bad sending unit, wiring issue, or actual low oil pressure. I'm 100% confident it isn't a stepper motor issue. Bad stepper motors don't cause a low oil pressure message to set on the DIC.

and as Tom suggested, a mechanical gauge to test that and see if it is actually low

 

[Ron Nielson]

One thing is for sure if the oil pressure was actually at 0, no oil pressure, your engine would be knocking within a few seconds

 

[05 Fifth Wheeler]

and as Tom suggested, a mechanical gauge to test that and see if it is actually low

The issue has reoccurred for the past 5 years and I have learned to live with it. It is intermittent in that I can go many days and even 1000's of miles with no problem. When the issue arises a slight increase in rpm will shut the alarm and message off. It may or may not happen at the next traffic light. If it doesn't reoccur the oil pressure will be between 0 and 1/4 at low idle. I am planning on selling the unit and would like to have the issue resolved. As stated the engine runs very smoothly, has about 200,000 original miles and has been very well maintained. I am thinking an ohms resistance check on the wiring from the sender to the ECM might identify the problem but because of the intermittence it may not. Could the problem be in the ECM? Should all 3 wires just be replaced? What about installing a mechanical or electrical pressure sensor and gauge? Can the old sensor just be disconnected or will the alarm be activated constantly? Where can a reasonably priced electronic pressure gauge be purchased.

 

[2004LB7]

I would not try and bypass it in any way. those sensors are a three wire sensor so you can just disconnect it without freaking it out. get a mechanical gauge and hook it up. doesn't have to be anything fancy. verify the reading when you get the warning. you can always try a new sensor if the mechanical gauge shows pressure

if you have no pressure then you need to start looking at either selling it with that as a known problem or opening up the engine to see whats up. may be a worn oil pump or the engine is worn to the point of dropping too much pressure. I believe you are overthinking this