Hi there everyone, this will be my first post here. I hope it’s not too redundant.

I just bought a 2008 Silverado 1500 that has the 5.3L vortec flex fuel motor with 137,000 miles on it. Four days after buying it I get a CEL. At the same time I noticed oil pressure was around 18-20psi at idle (600-700rpm) with engine warm. Did a scan and it showed P0521, oil pressure sending unit. Cleared the code and it came back less than 24 hours later. So today I got a new sensor and screen to fix it.

I removed the old sensor (which showed no sign of thread lock on it). I fished around trying to remove the old screen forever because apparently they can be tricky to get out. After an hour both my buddy and I agreed there wasn't one in there to replace. Put new screen in and installed new sensor.

Here’s where I have an issue. I looked online and came up with three torque specs for the sensor (11, 15 and 26ft/lbs). Autozone had a guide so I followed it and torqued to 26. I noticed that this put the locking tab about 90 degrees past where it was originally. Is 26ft/lbs too much?

After installing new sensor, readings are about the same. 20-22psi at idle parked in driveway, 35-38 psi at 2000rpm with warm engine. The needle doesn’t bounce around now. Are these pressures ok/normal? It’s been hard to find a definitive answer online as to what normal operating pressures are. The engine has always been quiet since my first test drive. There is no knocking or ticking even when revved to 2000rpm before or after replacing sensor. Oil level is good and is in good shape with 95% oil life left.

Thanks for any answers or advice!






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Your pressures seem to meet minimums.
The layman rule of thumb is 10psi per 1000 RPM.
The pressure relief valve should start kicking in around 60 psi, so your pressure seem "safe".
You may find that if you change oil formulations, or filter brands, the pressure will change.

by the way, there shouldn't be any thread lock (which is super glue) on the sensor threads. Just sealant.

My sources say

1. Tighten the fitting to 15 N·m (11 lb ft).
2. Increase torque until the centerline of the fitting (1) is 50 degrees from the centerline of the crankshaft.

 

The New part had some red stuff on threads. I was assuming it was thread lock. So if I torqued to 26ft pounds what should I do now? Any advice would be greatly appreciated.

BTW truck started fine this morning but pressure 35. Outside temp 40 degrees. Stayed right around 30psi on my 10 mile commute (1800 rpm @60mph). Was back down to 20 or just under when I parked it.

Im just worried I might have bought a truck with a bad pump or o-ring. I don’t have the money to have that fixed.

 

It's in there now. Just leave it.

If your pump/oring was bad, then pressure would be too low.

Just keep an eye on it, but I think you're fine. Happy driving.

 

Thank you for the reply. That’s the thinking I had but it’s always nice to hear someone else say it 👍🏻

 

I checked the oil level totally cold today and it was a bit low. Looked in great shape though. Added 1/2qt of 5w30 castrol edge full synthetic because that’s what I run in all my GM vehicles. Next oil change it will also get a Fram untra guard filter.

 

OP, I recently purchased a 2013 with 102k on the 5.3L. The day after bringing it home, I drove to the store about 15 miles away. During the drive, the CEL came on, so I checked the oil and it wasn't low. Oil pressure was lower than it should have been, tho, just like yours. Hooked up my code scanner when I got home, and it was a P0521, just like yours. My first thought was, "Oh, crap...what have I gotten myself into?" Did a little research, and found that there was a TSB from GM that might explain the issue. I'll see if I can find the link, but essentially it said that the AC Delco PF48E filter, which is what is specified in the manual, can cause low oil pressure indications. If so, it should be replaced with the UPF48R filter. I looked under the truck and could see that it was a blue oil filter, so I suspected that it was probably a PF48E. A little further research indicated that the Mobil M1-113 filter was identical to the UPF48R filter, and was available at my local AutoZone store. So I bought 6 quarts of Mobil1 5W-30 and an M1-113 filter and did an oil change. Lo and behold, the oil pressure went right back up to 43+ on a cold start, 40 driving down the road, and 30-35 at idle. Problem solved, to my great relief. Good luck with yours!

 

Here's the link I referred to:

https://www.obd-codes.com/pdf/gm-tsb-pip5276d.pdf

 

Another possibility:

https://static.nhtsa.gov/odi/tsbs/20...59078-4342.pdf

 

Most aftermarket sensors that are exposed to liquid will have some kind of sealant on them. The oil pressure sensors on GM vehicles also use a crush washer as an added measure of protection against leaks. Don’t worry about the sensor tab not being in the original spot - if you had over torqued it too much, you’d be asking the best way to remove the part that broke off.

I could be mistaken, but I don’t think GM started adding screens to the sensor hydraulic circuit until AFM (displacement on demand) was introduced because the cylinder shut off circuit is fed from the same one as the sensor. If your truck doesn’t have that feature, there may not have been a screen at all or it could have been removed by the PO.

To verify your pressure gauge and sender is working correctly, you can wiggle test the harness with the engine running while a helper watches the gauge for erratic activity. If you really want to verify it, get a mechanical gauge to test it (a fuel pressure tester will work if you can adapt the fitting).