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2019 Black Denali HD L5P
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Discussion Starter #1
i have an 08 LMM and once i drive about 10 or 15 miles and slow down then accelerate, like a stop light or turn or stop sign etc, it dings and message board reads "low oil pressure, stop engine.'' the oil pressure gage is reading just under 30 and rides at that pressure all the time. the chevy mechanic says thats where it should ride. any info on this problem would be greatly appreciated
 

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That's about right. As to why the dash light comes on Idk. You think if the sending unit was bad the gauge wouldn't work. Oil level good?
 

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Here is the GM PI/TSB regarding the common low oil pressure issue.
I highlighted the most important step.

PIP4682 Low Oil Pressure Warning Or Indicator - keywords 6.6 6.6L chime cluster diesel engine gage gauge IPC LMM panel - (Aug 6, 2009)

Subject: Low Oil Pressure Warning or Indicator


Models: 2007-2009 Chevrolet Express, Silverado

2007-2009 GMC Savana, Sierra

Equipped with the 6.6L diesel engine RPO code LMM


The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A dealer may encounter a customer concern of a low oil pressure warning or indicator.

The customer concern will be a low oil pressure warning coming on when slowing to a stop, in high ambient temperatures, and after being driven at highway speeds. The warning may not come on until the vehicle actually makes the stop, then the vehicle is accelerated. The instrument panel gauge may not show pressure below 206KPa or 30 PSI.

Recommendation/Instructions:
Complete the normal SI diagnostics for low oil pressure. Verify oil pressure reading with a mechanical gauge.

The SI specifications for oil pressure are:

Oil Pressure - Minimum- Hot - at idle is 98 KPa/14 psi

Oil Pressure - Minimum - 1800 RPM - 294 KPa/42 psi

A dealer technician may notice the oil pressure (on the mechanical gauge) is reading at or near 82-96 KPa (12-14 PSI) when the indicator has been noticed.

Engineering is investigating these low oil pressure indication concerns with a focus on the oil pressure monitoring system calibration. Please provide a product report (using newest version of bulletin 02-00-89-002) if a vehicle exhibits this condition.

Verify customers have followed proper oil change intervals. Change the oil with a diesel rated 15W-40 oil (following diesel supplement owner's manual instructions) before diagnosing any low oil pressure concerns. With fresh oil installed, evaluate the engine oil pressure with engine temperature at 85* C (185* F) for 15 minutes.

If the oil pressure is 8 PSI or higher do not attempt engine or gauge repairs.

If oil pressure is below 8 PSI, continue with the SI diagnostics for low oil pressure, and make necessary repairs.

Note: The instrument panel gauge is buffered. The actual reading taken with the mechanical gauge may not correspond with what is seen on the instrument panel gauge. Rely on only the mechanical oil pressure gauge for this diagnosis.

CC
 

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"Condition/Concern:
A dealer may encounter a customer concern of a low oil pressure warning or indicator.

The customer concern will be a low oil pressure warning coming on when slowing to a stop, in high ambient temperatures, and after being driven at highway speeds. The warning may not come on until the vehicle actually makes the stop, then the vehicle is accelerated. The instrument panel gauge may not show pressure below 206KPa or 30 PSI
."

That describes exactly what my truck was doing a couple of weeks ago. It was 101 degrees and I was pulling my 30' toyhauler down the highway. When I got into town, I would get the warning every time when taking off from a red light. My gauge never read less than 28 PSI. Since this is obviously a know issue I wonder why GM doesn't fix it. I always keep an eye on my gauges so if they give false information, what good are they? Gauge sits at 28-30 psi when at highway speeds. (around 1600-1800 rpm)
 

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Same thing happening here with my 2007.5 in very hot weather. Have never seen before, and have seen where this may occur more with synthetic oil, which I went with (Rotella T6 I believe) on my last change.
 

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The oil pressure gauges in these trucks are the worst! I never understood how my CTS could read more accurate pressures using the same sensor as the dummy gauge on the dash does... You'd think that GM could've put more time into something that vital to watch. My gauge on the dash tends to hang around 30psi all the time once up to operating temps.

Watching EOP on my CTS shows a normal of 18psi-60+psi depending on temps and run time. The lowest I have ever seen my oil pressure was 16psi at idle (38psi cruising) on a HOT day towing a 12k lb load. I have never had the low oil pressure light come on though.

PS: I run Rotella T6 as well
 

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wondering what grade and who's oil you're using??
 

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The oil pressure gauges in these trucks are the worst! I never understood how my CTS could read more accurate pressures using the same sensor as the dummy gauge on the dash does... You'd think that GM could've put more time into something that vital to watch. My gauge on the dash tends to hang around 30psi all the time once up to operating temps.

Watching EOP on my CTS shows a normal of 18psi-60+psi depending on temps and run time. The lowest I have ever seen my oil pressure was 16psi at idle (38psi cruising) on a HOT day towing a 12k lb load. I have never had the low oil pressure light come on though.

PS: I run Rotella T6 as well

Exactly what he ^^^^^^^^ said.
I run Rotella T6 as well year round.
 

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when I first get in my truck 2500HD Duramax Diesel my oil pressure is at 60psi, after a few miles it goes to around 30psi, and remains there. I just started noticing this issue.
 

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I switched to a thicker oil and warnings went away.
 

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Correct Oil Pressure

Isolate the condition in which the low oil pressure is coming on. Engine cold at idle vs eng hot at idle. Remember the analog guage showing near 30 psi isnt really what the ECM sees, its actually around 16psi. The higher the guage reading the more accurate to the ECM's reading. The lower the guage reading the ECM is seeing almost half that pressure (this is normal for analog pressure guages from GM). If low oil pressure after engine hot and running hard, chances are you have a leaking injector that has contaminated your fuel as this degrades the viscosity at higher temps. An oil change and filter can isolate this problem as it may take several days for the problem to come back (in which the injector is leaking fuel in the crankcase during engine off). Few times I have seen the filter bypass valve (presure relief valve) to fail by sticking open when hot. Cheap and simple to replace - in filter housing, only have to remove filter to replace. Almost always the relief valve is the problem for too high oil pressure. I only rule an oil pump after checking all other possible reasons and then inspecting the main bearings - not recommended for amateurs. I always reccomend using the oil type GM advises to - I'm not an oil expert but sometimes you have to keep it simple to eliminate problem concerns. Hope this helps give you an idea for the right direction.
 

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Here is the GM PI/TSB regarding the common low oil pressure issue.
I highlighted the most important step.

PIP4682 Low Oil Pressure Warning Or Indicator - keywords 6.6 6.6L chime cluster diesel engine gage gauge IPC LMM panel - (Aug 6, 2009)

Subject: Low Oil Pressure Warning or Indicator


Models: 2007-2009 Chevrolet Express, Silverado

2007-2009 GMC Savana, Sierra

Equipped with the 6.6L diesel engine RPO code LMM


The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A dealer may encounter a customer concern of a low oil pressure warning or indicator.

The customer concern will be a low oil pressure warning coming on when slowing to a stop, in high ambient temperatures, and after being driven at highway speeds. The warning may not come on until the vehicle actually makes the stop, then the vehicle is accelerated. The instrument panel gauge may not show pressure below 206KPa or 30 PSI.

Recommendation/Instructions:
Complete the normal SI diagnostics for low oil pressure. Verify oil pressure reading with a mechanical gauge.

The SI specifications for oil pressure are:

Oil Pressure - Minimum- Hot - at idle is 98 KPa/14 psi

Oil Pressure - Minimum - 1800 RPM - 294 KPa/42 psi

A dealer technician may notice the oil pressure (on the mechanical gauge) is reading at or near 82-96 KPa (12-14 PSI) when the indicator has been noticed.

Engineering is investigating these low oil pressure indication concerns with a focus on the oil pressure monitoring system calibration. Please provide a product report (using newest version of bulletin 02-00-89-002) if a vehicle exhibits this condition.

Verify customers have followed proper oil change intervals. Change the oil with a diesel rated 15W-40 oil (following diesel supplement owner's manual instructions) before diagnosing any low oil pressure concerns. With fresh oil installed, evaluate the engine oil pressure with engine temperature at 85* C (185* F) for 15 minutes.

If the oil pressure is 8 PSI or higher do not attempt engine or gauge repairs.

If oil pressure is below 8 PSI, continue with the SI diagnostics for low oil pressure, and make necessary repairs.

Note: The instrument panel gauge is buffered. The actual reading taken with the mechanical gauge may not correspond with what is seen on the instrument panel gauge. Rely on only the mechanical oil pressure gauge for this diagnosis.

CC
I have an LMM and you described exactly what I'm currently going through, my analog gauge reads normal and never drops below GM spec...was your issue electrical?
 

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Discussion Starter #13
I have an LMM and you described exactly what I'm currently going through, my analog gauge reads normal and never drops below GM spec...was your issue electrical?
I never found out. I actually got a new truck shortly thereafter. I have often wondered if anyone ever figured out the issue because the GM mechanics never could
 

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I never found out. I actually got a new truck shortly thereafter. I have often wondered if anyone ever figured out the issue because the GM mechanics never could
Good thing you got rid it when you did...I had both pans dropped in order to replace the oil pump and found a plugged up oil pickup tube, lots of gunk through out the engine and worn out crank bearings. The previous owner obviously abused this engine from lack of oil changes...now I am currently replacing it with a factory rebuild because the bones of my current one is no good
 
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