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Ron. I have a 2008 GMC Yukon Denali with 150k miles that has…

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Hi, Ron. I have...
Hi, Ron. I have a 2008 GMC Yukon Denali with 150k miles that has been dealer maintained since purchase, had oil changes at least every 3k miles and all other suggested maintenance done. For the past two weeks, we are getting an "Oil Pressure Low, Stop Engine Now" light/alarm at startup on most days. It goes away when the engine warms up. Took the car to the dealership and they said it was a switch (sensor?). $750 to replace the switch and change the oil and filter, and they tested the oil pressure while it was in the shop and said it was fine. We have not had any leaks from the car, ever.When I went in to pick up the car, the oil alarm was literally going off as he handed me the keys in the lane. I sent it back to the shop and, a week later, they told me they have only seen this one other time before and it needs a new engine - for $8k. Picked up the car yesterday and the oil pressure alarm was still going off in the lane and, for the first time, the engine sounded a little rough. Not knocking, but not quite right. I drove the car home and watched the oil pressure gauge. It's around 40 at most speeds, but drops pretty quickly at idle (stopped at a light) and then the pressure alarm goes off. Engine doesn't stall. Oil alarm turns off if I put some RPM's on the engine. Seems to stay steady around 40 psi above 1k RPM's.We were planning on selling or trading in the car in the spring but may do so sooner; however, I will not sell a car outright with a potential big issue and now I may not get anything on a trade-in if I have this alarm going off. I've been searching some forums and I think there are some other things to try/ask first:
- ask if the filter right under the sensor is clogged? Unfortunately, mechanic told me the switch was located in a tough spot to change, that's why it took so much labor. I have no idea if he checked the filter (or if I can trust him if he said he did) or can do so easily now.
- can they check to see if the oil pump is clogged? There was no discussion about the oil pump.
- change the o-ring and see if that does it, but I have no idea at what cost
- increase idle speed for now to keep the alarm away and trade in the car asap
- put a different oil in that will temporary help the problem and trade it in.Thoughts?
Submitted: 8 months ago.Category: GMC
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Answered in 2 minutes by:
11/21/2017
GMC Mechanic: Pete, GMC Mechanic replied 8 months ago
Pete
Pete, GMC Mechanic
Category: GMC
Satisfied Customers: 33,011
Experience: GM training and dealer tech for 14+ years. Diagnostics
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Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Did they replace the engine already to try and correct this issue?

Let me know,thanks Pete

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Customer reply replied 8 months ago
No, they just replaced the switch, checked the pressure on the system (good) while it was in there, and changed the oil and oil filter. When I picked up the car and the "low oil pressure" alarm was going off in the lane when they brought it around, they sent it back in for assessment and told me the only way they knew to solve the problem was to put in a new engine. We picked up the car without doing that and are trying to decide what to do next.
GMC Mechanic: Pete, GMC Mechanic replied 8 months ago

O.k.,one of the more common causes I have seen for low pressure at idle or low rpms but good pressure when raising the engine speed is sludge build up in the oil pump pick up tube in the engine oil pan.The other issue I have seen is a fault with worn or damaged engine crank shaft or cam shaft bearings.

They need to perform an actual engine oil pressure test with an engine oil pressure test gauge.If the pressure is found to be low at idle or low speeds then I would have the oil pick up tube checked for sludge build up needing cleaned and the bearings will need checked.

Now if the bearings do have damage to them or wear then the camshaft and crank shaft needs checked for weak to determine if it is worth repairing or just replacing the engine all together.

This is what I would have done/checked next here.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

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Customer reply replied 8 months ago
They did the engine oil pressure test when they were checking out the fault and decided to replace the switch. The report says "performed mechanical oil pressure test -ran engine for 1 hour while monitoring. Oil pressure passed mechanical test with 22 psi at idle. Replaced oil pressure switch and verified repair. P0522 passed after repairs." But, two days later when the engine was cold and they brought the car around for us to pick up, the "low oil pressure - Stop engine now" light/alert was back on.
GMC Mechanic: Pete, GMC Mechanic replied 8 months ago

O.k., it sounds like your actual oil pressure is o.k.Did they re test the oil pressure again after the issue came back to verify the pressure is still at the 22 psi at idle?

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Customer reply replied 8 months ago
Is it costly (labor intensive) to check the oil pick up tube for sludge build up? Or to check the bearings? Are you talking about the bearings in the oil pump or the crank shaft bearings (internal to engine)? If these are tough to get to or costly, what can we do in the meantime to make the alert go off?
Customer reply replied 8 months ago
I don't think they retested. Just told us that the only thing that would solve he problem for sure was a new engine.
Customer reply replied 8 months ago
I don't think it's a sensor. I think the oil pressure is actually dropping when at idle. It's too easy to replicate now every time I drive the car, it's consistent. Fine at 40 psi when RPMs are above 1000, around 500 RPM's (stop light idle), oil pressure slowly drops to the point where the alert comes on. Goes away as soon as I put RPMs on the car, or if I keep my foot on the gas and brake and add RPMs without moving.
GMC Mechanic: Pete, GMC Mechanic replied 8 months ago

O.k.,it does sound like the pressure is dropping at idle.This is usually a sign of a worn bearing on the crank shaft or cam shaft or oil pick up tube full of sludge.The bearings I am speaking of are the camshaft and crankshaft bearings.These can cost over $1000 to have replaced and then if it is found the actual crankshaft has damage to it then it would need replaced which can cost another $1000 in some cases so it may be best at that point to replace the engine.It does require taking the engine apart to gain access to these engines and in some cases engine removal is easier to then dissasemble to inspect and replace.But is is usually cheaper to replace the engine at this point then to spend the money on labor to inspect and replace bearings.

I would have them remove the engine oil pan though and check the oil pick up tube for oil sludge build up needing cleaned out.Unfortunately nothing can be done to get rid of the alert as the pressure is to low it will send this message.Even if the switch/sensor was disconnected it would cause this issue.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time,this can be done at any time and you can still come back here and reply if needed.Your 5 star rating is appreciated

Thanks Pete

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Customer reply replied 8 months ago
I can have them check the oil pick up tube for oil sludge build up. Is this the same filter right under the oil sensor that I have seen in other posts to check?
What about the O-ring that I have also seen people say can solve this problem?
Thanks.
GMC Mechanic: Pete, GMC Mechanic replied 8 months ago

That is a screen that is plastic.It is common to build up sludge and sends a false signal to the oil sensor and causes this issue.This is why it is a good idea to first tell them to test the oil pressure again.If found it has good oil pressure at idle again then I would have this screen/filter removed and cleaned or replaced.

I havent heard anything about an o ring issue on this year and model vehicle myself but the screen/filter was a common fault.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time,this can be done at any time and you can still come back here and reply if needed.Your 5 star rating is appreciated

Thanks Pete

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Customer reply replied 8 months ago
What is the screen/filter you are talking about to have removed and cleaned or replaced? Is it located by the switch, which was very labor intensive to get to? Sounds like they should have done it when they replaced the switch and were there.I can also have them check the oil pick up tube for oil sludge build up. It sounds like that one is accessed by removing the oil pan.Trying to think of things to try to solve the problem before I lose all value on a car currently valued at about $8k or have to put in an $8k engine. Just doesn't make sense for us.
Customer reply replied 8 months ago
is there anything with the oil pump that can be looked at for sludge or poor flow that might be reducing oil pressure at low RPM's? Again, the pressure goes right back up to 40 psi with any sort of RPMs on the engine. It just drops at idle and then the alert comes on. Goes away as soon as I put RPMs on the engine and the pressure pops back up. Very replicable.
GMC Mechanic: Pete, GMC Mechanic replied 8 months ago

Re checking the info on your model you do not have the screen/filter.Your oil pressure sensor/switch is located in the oil pan itself so this is a different set up then normal on your engine.In most cases it is not the oil pump as this is a gear driven pump and if it was you would not see any oil pressure at all.

This sounds like sludge build up or worn bearings causing this fault.It is your call but the engine oil pan would need removed to inspect for any sludge in the pick up tube.

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time,this can be done at any time and you can still come back here and reply if needed.Your 5 star rating is appreciated

Thanks Pete

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Customer reply replied 8 months ago
Just called the shop who replaced the switch and they said that they checked the screen/filter when they did so because it's a common problem for it to build up sludge there. They had to take a bunch of stuff apart to get to the switch (not just the oil pan off) because it's buried behind the engine. Therefore, the 5 hours of labor to replace a $59 part and check the screen. What you are telling me is different from what they are telling me about this screen and the location of the switch, so I assume they know because they have seen the car.If it was worn bearings, I don't think we'd have this situation that is always the case: low/dropping oil pressure at idle but up to around 40 psi with RPMs over 1k. The car is behaving predictably with the oil pressure behavior. Just trying to figure out what would cause low oil pressure at low RPMs that increases always with more RPMs. The shop told us that bearings will cause the engine to get out of sync and the oil pressure will be all over the place when it gets into that mode because the flow of oil is interrupted and this could happen at any RPMs. What I'm seeing doesn't sound like this.
GMC Mechanic: Pete, GMC Mechanic replied 8 months ago
The screen they are most likely talking about is the pick up tube screen itself.I don’t see another screen in there unless one was placed in the oil pan insert where the switch was located but my info is not showing that.It sounds like they checked and cleaned the screen and most likely the pick up tube.
Lower engine speeds causes lower oil flow.Engine bearings help to keep oil pressure up due to how snug they are against the cam and crank.Oil flows through or across these bearings.When a bearing wear issue occurs where there is some slack in a bearing it will cause low pressure at lower rpm’s then as the engine is revvee up the pressure climbs as the pump is working faster.
It is possible there is somewear to the oil pump causing low pressure at low rpm’s but usually you would see low pressure at all times.But I wouldn’t rule out the pump as the cause,it just sounds unlikely from here.
The best thing to do here is have the oil pressure tested again with an oil pressure test gauge.If it is found to be at least 15 psi at idle then the issue is not mechanical but is electrical and since the switch did not repair the fault the wiring and computer signal needs tested to locate the fault.
If the pressure is actually found low then you would need to have the pump and bearings checked.Then it can be determined by you from there if you want to repair the fault once it’s found or if you want to just put a replacement engine in it.Thanks Pete
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