LS4 P0521 *After* replacing VLOF and sensor?
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The AFM pressure relief valve limits pressure to 55-65 psi.
P0521.....
The ECM detects that the difference between the predicted oil pressure and the actual oil pressure is either less than 6.8 psi or greater than 7.3 psi.
The calibrated pressure range is 6-65 psi.
So the pressure input would need to be Zero or above 72.2 psi for P0521 to set.
*I would really like to see the Freeze Frame/Failure Record, But it's looking like a bum aftermarket sensor.
P0521.....
The ECM detects that the difference between the predicted oil pressure and the actual oil pressure is either less than 6.8 psi or greater than 7.3 psi.
The calibrated pressure range is 6-65 psi.
So the pressure input would need to be Zero or above 72.2 psi for P0521 to set.
*I would really like to see the Freeze Frame/Failure Record, But it's looking like a bum aftermarket sensor.
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Originally Posted by clinebarger
The AFM pressure relief valve limits pressure to 55-65 psi.
P0521.....
The ECM detects that the difference between the predicted oil pressure and the actual oil pressure is either less than 6.8 psi or greater than 7.3 psi.
The calibrated pressure range is 6-65 psi.
So the pressure input would need to be Zero or above 72.2 psi for P0521 to set.
*I would really like to see the Freeze Frame/Failure Record, But it's looking like a bum aftermarket sensor.
Priceless info, thanks for this
! The third sensor is on there now. This one is identical to the first replacement that lasted several years. The one I got last month was very different, and seemed low quality. Hopefully this one lasts a few years like it's twin. If not, Delco it is. The only reason I haven't already bought a Delco is due to the lifetime warranty, they cost nothing. But three strikes, you're out...
The AFM pressure relief valve limits pressure to 55-65 psi.
P0521.....
The ECM detects that the difference between the predicted oil pressure and the actual oil pressure is either less than 6.8 psi or greater than 7.3 psi.
The calibrated pressure range is 6-65 psi.
So the pressure input would need to be Zero or above 72.2 psi for P0521 to set.
*I would really like to see the Freeze Frame/Failure Record, But it's looking like a bum aftermarket sensor.
Priceless info, thanks for this
Originally Posted by mattd
I would say you may have a sticking pressure regulator or relief valve. You should have MUCH more pressure than that at that cold of a start.
So by pressure regulator, we're referring to the sensor I've already replaced, correct (pictured below)? Assuming yes, I'm curious about this relief valve. I'm assuming this is not the bypass valve located in the oil filter. It's somewhere within the engine, I'm guessing part of the oil pump? Thanks for the input!
I would say you may have a sticking pressure regulator or relief valve. You should have MUCH more pressure than that at that cold of a start.
So by pressure regulator, we're referring to the sensor I've already replaced, correct (pictured below)? Assuming yes, I'm curious about this relief valve. I'm assuming this is not the bypass valve located in the oil filter. It's somewhere within the engine, I'm guessing part of the oil pump? Thanks for the input!
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The Pressure Regulator Valve is in the Oil Pump, The AFM Oil Pressure Relief Valve is located right above the oil filter behind a cover (Unique to the LS4).
![[Linked Image]](https://i.imgur.com/zAvA2fa.png "[Linked Image]")
***Update***
Bad news... It's not the sensor.
Had time to hook it up again tonight with a cold start (about 50°F again). When it started, it slowly and steadily built pressure up to about 40psi over the first two full seconds (no instant burst of pressure). It held steadily at ~40psi until the idle started to slow, then the pressure fell. It fell to 24psi. What's really bizarre is it fluctuated between 22-44psi for the entire warm-up cycle. I recorded about 5 minutes of the pressure test to give a better idea of what's happening (sorry! I did the one thing I can't stand, I held the phone upright...
). The video starts about 1-2 minutes after the cold start, but essentially you only missed the first 15 seconds, because after 15 it does the same thing until the video starts. Here's a YouTube link:
Pressure Test Video Link
I guess it's comforting knowing it didn't fall below 22psi
I'm debating the scenarios in my head, wondering if it's worth it to fix it... I'd probably use OEM parts, and have it dealer serviced (because I have connections with employee discounts on both parts and labor). If this is the AFM pressure relief valve, how much will it cost to fix (or is this easy enough to do myself)? Looking for hours and part cost, I can calculate the rest. Or if it's the pressure regulator, what's the time and part cost there? I'm assuming it's a full oil pump replacement, and I'm assuming it's a LARGE number on the labor side. I definitely won't do this one myself...
Huge thanks again!
Had time to hook it up again tonight with a cold start (about 50°F again). When it started, it slowly and steadily built pressure up to about 40psi over the first two full seconds (no instant burst of pressure). It held steadily at ~40psi until the idle started to slow, then the pressure fell. It fell to 24psi. What's really bizarre is it fluctuated between 22-44psi for the entire warm-up cycle. I recorded about 5 minutes of the pressure test to give a better idea of what's happening (sorry! I did the one thing I can't stand, I held the phone upright...
Pressure Test Video Link
I guess it's comforting knowing it didn't fall below 22psi
I'm debating the scenarios in my head, wondering if it's worth it to fix it... I'd probably use OEM parts, and have it dealer serviced (because I have connections with employee discounts on both parts and labor). If this is the AFM pressure relief valve, how much will it cost to fix (or is this easy enough to do myself)? Looking for hours and part cost, I can calculate the rest. Or if it's the pressure regulator, what's the time and part cost there? I'm assuming it's a full oil pump replacement, and I'm assuming it's a LARGE number on the labor side. I definitely won't do this one myself...
Huge thanks again!
For hot idle to be good and cold idle to be low, it seems to me the problem would have to be a leak or restriction before the oil pump; either the pickup o-ring is leaking (likely), or the screen is clogged.
Apparently it's possible to get the oil pan off yourself with some minor difficulty. See this Impala Forum thread. I wouldn't want to guess dealer hours.
Apparently it's possible to get the oil pan off yourself with some minor difficulty. See this Impala Forum thread. I wouldn't want to guess dealer hours.
Also, would there be any harm in driving the vehicle until I decide what to do? I've been driving it like this for who knows how long...
It took me about 6 hrs total to support the engine in place and to drop the cradle and pan on a W body 3800, I imagine its similar. Replace the front mount while its out, you have to partially go though the same fiasco and at 133K and 11 years its getting there, use OE only, its about $100.
If it is the O ring or regulator there is no telling when it could totally fail but if it does it could cost you the engine. IMO its prudent to stop using the car with an oiling issue until its been repaired.
If it is the O ring or regulator there is no telling when it could totally fail but if it does it could cost you the engine. IMO its prudent to stop using the car with an oiling issue until its been repaired.
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