2008 Grand Prix GXP LS4
 

I am getting the Service Engine Light often on my GP. The code is P0521--Oil Pressure Sensor Error. I've noticed this is a common problem for the LS4 engines in Pontiacs, Chevs, & Chev/GMC trucks.

Car has 160,000 miles on it. No abnormal engine noises--runs fine, uses about 1 qt. oil each 2000 miles, which is normal for these LS4 engines.

I've replaced the oil pressure sensor and screen below it. The problem still appears within a few days after resetting the trouble code.

Anyone have a likely solution for this problem? .

https://www.obd-codes.com/p0521
Check out the TSB links.

I have replaced the sensor and screen below it with no change in symptoms. I just changed the oil using synthetic 10w-30 and an AC filter. Oil is exactly on the full mark of the dipstick.

When I reset the code, the service engine light comes on sometimes when starting the engine and sometimes while driving with a warmed-up engine.

Next, I'm going to try taking off the pressure sensor plug and putting dielectric grease on the three terminals.

Any other ideas?

One of TSBs refers to a DTC PO521 code using another GM/Delco oil filter part #UPF48R. That sounds like a far reach that a different oil filter is going to stop it from setting a code. However it's not going to cost a bunch of money to try it.

Then they talk about the screen in the oil manifold, which I assume is the screen you have mentioned.

There is also talk about doing an ohm reading on the oil pressure switch, which you already say you've replaced, but just because a part is new doesn't mean it's good. I can think of a few times new parts came out of the box defective. Just something worth keeping in mind before you tear your hair out chasing a non problem.

Have you put a mechanical gauge on it to verify what the oil pressure actually is?

A stuck by pass valve, weak or broken relief spring in the oil pump, could also cause it.

Checking oil pressure with a mechanical gauge would show an actual oil pressure problem. Then you have to hunt down the mechanical problem. I would want to verify that the mechanical portion was up to snuff before chasing electrical gremlins.

That's how I would approach the diagnostics, just my :2cents:.

Good thinking, Sirrotica. I need to figure out where to put a pressure gage so I can determine the real oil pressure.

Probably a tee fitting between the engine and the sending unit would give you a port for the mechanical gauge, and keep the sending unit operable while running the mechanical gauge at the same time.

If that's not practical because of space limitations, you can buy a spacer called a sandwich adapter, that screws on to the engine and the oil filter then screws on to the adapter. It has threaded ports (pressure and return) that you can tap the mechanical gauge into. They usually come with pipe plugs in the ports so you can choose what port you need to use. The sandwich adapters are used mostly to plumb oil coolers or remote filters into the oil system, but if you were space limited and couldn't use a Tee fitting to tap into between the engine and sending unit, one of these adapters should work fine.

Here's a link to The sandwich adapters: https://www.amazon.com/s/?ie=UTF8&ke...l_7jyovfn4uh_e

I have a Frantz by pass oil filter on my LS2 GTO and use one of the sandwich adapters to plumb it into the system.

If your putting in a pressure switch you will need a special adapter. to run the gauge to, Its metric. A good way that works to do this and is cheap is the use the old sending unit and then drill and tap it to take the gauge .Works great. We had the same problem on are GXP build but after we charge the sender with a new A/C Delco unit, and it was fine. We first checked it with a gauge to make sure we had pressure Hope this helps you.

Thanks, Rocco. I suspected the LS's may be all metric. Good idea to use the old sending unit for an adaptor.

Your comment about a genuine AC sender is interesting. I don't remember if my replacement was AC--probably not.

Ya we used the GM A/C brand. Almost twice as much but common on 5.3 motors. to go bad fast. I'm an old school motor guy and builder, my son did the GXP for himself, We did cam, headers rockers, delete the 4 cylinder mode, different intake etc. We also built a bullletproof trans for the car which was the original problem. The car is a nightmare to work on, but super fast. We changed out every part when the motor and trans were out. and I mean every line, hose or sensor. The only one we didn't change was the oil pressure sensor because in was in a spot you could get to easy and it worked before the build. It didn't after for no reason at all.. I don't know if you know this, but one of the knock senors is behind the transmission tailshaft, if it goes bad you will need to pull the trans to get to it, LOL

Do you have a curved aluminum cover, held on with two bolts, right above your oil filter?

If so, it can be removed, then drilled & tapped for a oil pressure source.

There are some aftermarket replacement covers that are already drilled/tapped.

Lived with the intermittent oil pressure problem when the engine is cold for three years. No serious problems until yesterday, when a valve train noise (ticking) began. Diagnostic says number one cylinder misfire. Is there anything I can do to determine the actual cause short of tearing the engine apart?

Dick, any news on this? I don't have an LS4 but just curious.

Originally you mentioned the oil consumption was "normal" for an LS4. I would suggest it might be "common" but should not be expected as "normal".

Does your engine have Active Fuel Management with the displacement on demand lifters?

According to TSB stuff, GM suggested that excessive oil consumption can be a result of an oil spray discharged by the AFM relief valve. Under certain driving conditions and higher mileage (wear), this spray can result in piston ring deposits that result in excessive oil consumption.

Cleaning the pistons with proper use of upper cyl cleaner and installing a new design oil pan gasket that deflects the spray was to help resolve the oil consumption.

If it didn't, piston replacement might be indicated.

The low oil pressure in the LS4 seems commonly a result of a failed pickup tube o-ring and/or a weakened oil pump. The AFM screen getting crudded up is also a suspect but if you've checked it and replaced it or cleaned it and the code continues to be thrown I'd suspect the o-ring and may as well replace the pump at the same time to avoid doing the job twice.

Checking the actual pressure is certainly good advice before diving in but will likely confirm at least low idle pressure. And even if the pressure seems marginally acceptable, probably best to replace if you don't want to keep throwing the code.

The ticking might be a result of lifter issues and a consequence from the low oil pressure over time or just old age of the lifter(s).

Read this:

https://www.autoserviceprofessional....ifters-and-dtc

No special knowledge on my part and just curious if you've resolved the issue, always interested in learning!