How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Ron Z. Your Own Question
Ron Z.
Ron Z., - GMC Tech -
Category: GMC
Satisfied Customers: 18779
Experience:  18+yrs experience. State Inspector & GMC Diagnostics/Repair
Type Your GMC Question Here...
Ron Z. is online now
A new question is answered every 9 seconds

GMC envoy denali: I have a 2007 envoy Denali v8, 5.3L (78,000

This answer was rated:

I have a 2007 envoy Denali v8, 5.3L (78,000 miles), Tuesday while driving in the highway the “Low oil pressure /stop engine”. Come out in the instrument cluster, pull over open the hood, check oil it was ok, start the car again and not noise at all, drove for few miles and again the warning come out. Pull over and decide to tow the car to the GMC dealer; next day they call me apparently need to clean the “oil filter lifter valve or something like that”. I drove the car back home (45 miles away) everything was fine (40 to 45 in the oil pressure gauge).
Later in the evening while driving around the pressure started to go down again and the warning light was on “Low oil pressure stop engine”. I manages to make home; this morning was the same with the addition of the check engine light.
The performance of the car never change, it runs fine.
I scanned the vehicle (OBD II scanner) and the following code comes out: P0521engine oil pressure sensor/switch range/performance. Called the dealer were the car was service and they told me to bring it back…Really (45 miles from home)
Any ideas…What could be the problem?
Welcome! I'm Ron Z! I will do my best to answer all of your questions. Please remember to RATE my answer!

From what you are describing here, and with the Check Engine light pointing directly to a faulty sensor, it sounds like this very well may simply be a case of a failing Oil Pressure Sensor. As long as there are no engine performance issues, and there are no unusual noises in the engine, like ticking or knocking when the Low Oil Pressure light comes on, then more than likely, it's just the sensor. The Oil Pressure Sensor on this vehicle is located at the top, driver's side, rear of the engine, and the Intake Manifold will need to be removed to gain the proper access. There is also a special tool, Oil Pressure Sensor Socket that is needed to remove the sensor. It's a bit of a "bigger" job, so probably not the best job for a DIY'er, but definitely worth looking in to. While the sensor is removed, it is a good idea to manually check the "actual" oil pressure with a pressure gauge. If the actual oil pressure is within specs, then suspect the sensor itself as the root of the problem. I hope this at least gets you pointed to the right direction!
Customer: replied 4 years ago.

Truly I don’t heard any ticking or knocking, the engine runs fine and got power; The GMC advisor told me that the oil filter lifter valve was clogged, and just need to be clean. Apparently they did that, but as far as I understand (what he said) to do that the oil pressure sending unit needs to be remove and they check for oil pressure and it was fine. The gauge does not do it all the time just sporadically (dropping the oil pressure in the gauge) , what I don’t get is that if they have to remove the oil pressure sensor to clean what they call “valve lifter” because was clogged why don’t replace the sensor?

I think there is a bit of a misunderstanding here. Not quite sure what an "oil filter lifter valve" is, but it's not accessed via the pressure sensor. If anything, this would be accessed from behind the oil filter housing. This is on the lower half of the engine. The oil Pressure Sensor, as stated above, is top, left, rear of the engine, and the Intake Manifold needs to be replaced to access it. If they were going to go through all that work, and take a manual reading of the pressure, and it proved good, why did they not replace the sensor? Good question! The oil pressure sensors on GM 8-cylinders have always been known to be fairly common fail rate items. Over time, the internal resistance of the sensor tends to fail, and usually when the oil is hot and thinner, it reads the wrong pressure.

Here's a bit of insight as to how the oil lubrication system works (give you an idea of how the system works, and the components within):


Engine lubrication is supplied by a gerotor type oil pump assembly. The pump is mounted on the front of the engine block and driven directly by the crankshaft sprocket. The pump gears rotate and draw oil from the oil pan sump through a pick-up screen and pipe. The oil is pressurized as it passes through the pump and is sent through the engine block lower oil gallery. Contained within the oil pump assembly is a pressure relief valve that maintains oil pressure within a specified range.

Pressurized oil is directed through the engine block lower oil gallery and through the oil filter tube to the full flow oil filter where harmful contaminants are removed. A bypass valve is incorporated into the oil filter, which permits oil flow in the event the filter becomes restricted. A second valve, the active fuel management oil pressure relief valve is incorporated into the oil filter tube. The active fuel management oil pressure relief valve limits oil pressure directed to the upper oil galleries and valve lifter oil manifold assembly to 379-517 kPa (55-75 psi) maximum. When main oil pressure exceeds 379 kPa (55 psi), the active fuel management oil pressure relief valve exhausts excess oil to the sump.

Oil is then directed from the filter to the upper main oil galleries and the valve lifter oil manifold assembly. Oil from the left upper oil gallery is directed to the crankshaft and camshaft bearings. Oil that has entered both the upper main oil galleries also pressurizes the valve lifter assemblies and is then pumped through the pushrods to lubricate the valve rocker arms and valve stems. Oil returning to the pan is directed by the crankshaft oil deflector. The oil pressure sensor is located at the top rear of the engine.
Customer: replied 4 years ago.

I really appreciate your technical documentation; well I have not experience working on GM products; I am Automotive Engineer and work only in European market vehicles; converting them to meet the EPA and DOT USA regulations. (Most of my work is wiring and programming). But it makes sense what you say, when I get the car back yesterday it does not show evidences (manifold) of being removed, I don’t know how they check for oil pressure!!! Seems like the $$$ they charged me was just a taken to the cleaner. The replacement of the sensor is something that for sure I can do. (If was able to swapped the engine and transmission in my wife Honda odyssey I can do this too) THANKS YOU VERY MUCH YOUR HELP IS VERY MUCH APPRECIATED…

WIth the P0521 present, I think you'll find the sensor is going to be the root of the problem. If the "actual" oil pressure was tested (although should have been tested through the sensor's mount) then the "pressure" is not the problem, and the way the pressure is "sensed" is.

I just wanted to add this to everything above, just so that you see every angle:

DTC P0521
  • -Engine Oil Pressure (EOP) Sensor Performance


Circuit Description

The engine oil pressure (EOP) sensor changes resistance based on engine oil pressure. The engine control module (ECM) monitors the signal circuit of the EOP sensor. When the oil pressure is high, the sensor resistance is high, and the ECM senses a high signal voltage. When the oil pressure is low, the sensor resistance is low, and the ECM senses a low signal voltage. The ECM sends the engine oil pressure information to the instrument panel cluster (IPC) via the class 2 serial data circuit.


Circuit/System Testing

Ignition ON, engine ON, verify the scan tool Engine Oil Pressure Sensor parameter is within 0.7 V-2.8 V .

If not within the range of 0.7 V-2.8 V , replace the EOP sensor.


Glad I could be of some help, and at least got you going in the right direction! Have a great day!


Ron Z. and 3 other GMC Specialists are ready to help you