GXPHelo

Hey I'm new to this forum but have noticed that there is a lot of good content on here. I just purchased a GXP and I got a check engine light on. I have paper work from a shop that has done most of the work on the car. It has a history of this code, P0521. Now I have done plenty of research and replaced the oil pressure sensor/switch with a brand new ACDelco one that I bought off eBay. I got the code cleared off and the light reappeared. I also pulled out and cleaned the little filter underneath with brake cleaner earlier in the week. And the mechanic before me put in a new plug to the sensor. So my question is where should I go from here? Should I return the sensor for a new one or should I just start checking the wiring and where the spliced the wires together? Thanks for reading.

impala06ss

Have you checked the actual pressure with a gauge?

Sint3k

This is going to be a little more complicated for you due to the nature of this code. The code is a "performance code", this means the computer is getting some type of unusal response it should not be from the sensor. This is a 3 wire design, there is a 5v reference, there is the signal circuit and there is the low reference circuit.

This is just be beginning, ultimately the code is set because

"The ECM detects that the difference between the predicted oil pressure and the actual oil pressure is either less than 47 kPa (6.8 psi) or greater than 50 kPa (7.3 psi)."

SO this can be a wiring issue, this can be a mechanical issue.

Lets get some facts out the way first:

The black wire on the oil sensor is the "Low Reference", This is what the computer uses to determine its baseline for "ground".

The Grey wire is the 5volt reference wire, there should be pretty much exactly 5 volts at this wire with Key On engine off, or key on engine running.

The Tan and white wire is then "Sensor Circuit", 4 volts for high oil pressure, 1 volt for low oil pressure "Roughly" So key on engine off, you'll read its lowest reading, "around 1 volt". Im not sure of its voltage at Idle, which is around 24"low" - 30-40" normal" PSI of oil pressure on an LS4.

So to start off with, the 5 volt "grey" wire needs tested to insure it is getting 5 volts

Next,

we need to make sure the black wire is a ground good ground with nothing causing high resistance. To do this you will need to do a voltage drop test. 1 lead of your DVM should be connected to battery negative, and the other should be connected to this black wire. you should see no more then 100milivolts, preferably way less. Another test for the black wire is to test the ohms reading, connect 1 lead to a GOOD ground, and the other to the black wire of the connector, in this case the connect will need to be unplugged does not matter if the key is in for this test.

Preferably, both test should be done with Key On, Engine running. If you can, report the voltage on the tan and white as to what the idle voltage is, also take note as to wether this voltage is steady or flucating greatly, and what it is flucutating between etc. Another test that can be done is with the connector unplugged, do a voltage test between the tan and white wire, and ground and report what the voltage is. I hope you write all this down and are detailed as to what is what It will help me from having to ask a repeat of questions .What Impala06ss posted previously is also a good idea as this code can very well be mechanical. Do you have a scan tool that can read live data ?

Let me know what you find and I'll try to assist you from there

Sint3k

I edited the above post many times, so please read it again if you read it awhile ago already. If you do test the oil pressure with a pressure gauge, the minimum should be

1,000 RPM 24PSI
2,000 RPM 35PSI
3,000 RPM 38PSI

these are all on the very "Low end" of what is expected at these RPM ranges. Add about 10-15PSI for "normal" pressure. These would be with the engine at operating temp.

superglide9375

again amazed,u prolly just saved the dude 200 in diagnostic charges,u can't get this stuff anywhere but here,thanks to all the guys on this site

Sint3k

I hope so, that took forever to type

GXPHelo

Thanks for the very detailed reply. I might not be able to check and run these tests till this weekend. If I had low to no oil pressure I would know by now right? I've been driving with this code for about 500 miles. Also, this car has a rebuilt engine in it that was put in by the previous owner, could this be causing issues like this one? Thanks again, I really do appreciate your help so far.

I should also mention that the CEL could be on one drive, then the next off. But it is on more than it is off.

rottonj

iTrader: (4)

Hook up an oil pressure gauge asap to find out if you really have low pressure. If you do its a mechanical problem and you should stop driving it, if not it might be alright to drive while sorting it out.

GXPHelo

I have a quick question, I read somewhere that if the sensor/switch wasn't receiving enough oil pressure, the engine would be locked on 8 cylinder mode only. Is this true?

91parkave

iTrader: (4)

Just buy another sensor be done

Sint3k

Well. ..that's the problem. ...he already did, according to his first post

Sint3k

The fact the connector pig tail was replaced tells me they know or knew something was up. Yes replacing the motor makes the chances of a wiring issue higher because they might of pinched a wire. To answer your question about the oil pressure, it only has to be off 6 psi to throw the code, plenty for the engine to still run

rottonj

iTrader: (4)

This should probably be moved to its own thread so there is no confusion to the original post.

Sint3k

I don't understand, is it not already in its own thread ?

rottonj

iTrader: (4)

I think I was on the pipe when posting . Reading too many threads lol.

Sint3k

Now this subject does require its own thread

GXPHelo

Sorry that I was unable to get back right away. I ended up trying a simple fix, changing oil. And guess what? It worked... For a week. The light stayed off for a whole week, but then came on the last drive. So I guess I will have to dig a little deeper than an oil change

rottonj

iTrader: (4)

Hook up a gauge.

GXPHelo

The gauge goes right where the sensor is sitting correct? And what do you do for a fitting on there?

rottonj

iTrader: (4)

Yes, and the gauge should be the same as I think it is standard, if not you will have to use adapters.