P0521 with low oil pressure

Tech discussions on the L77 6.0L V8.
s/c'd cav
Posts: 1215
Joined: Mon May 30, 2016 8:12 am
Location: PHOENIX AZ

Re: P0521 with low oil pressure

Post by s/c'd cav » Tue Nov 15, 2022 3:45 am

if only the DOD in my rainier(tbss clone) would work

it worked great before making a oil pan swap , ditched the awd hard parts , and swapped from the front sump pan to the C6 vette pan , and now it only works if my foot isnt on the pedal

and no codes

Caprice ltz
Posts: 11
Joined: Tue Sep 13, 2022 7:14 am

Re: P0521 with low oil pressure

Post by Caprice ltz » Mon Nov 28, 2022 2:29 pm

Has anyone tried the external gauge - not manual - ?

Posts: 91
Joined: Sun Aug 11, 2019 3:15 am
Location: East Central, PA

Re: P0521 with low oil pressure

Post by JRWolff » Mon Nov 28, 2022 3:25 pm

I've been chasing a similar issue on my stock L77 with 126,000 miles. P0521 code first came in at around 115,000 miles. I replaced the sensor with a new GM12621234 part. Problem did not return for another ~ 5000 miles. Took the car to a local dealer for further diagnosis. The claimed the oil pressure was actually low and would require at least $1500 for further diagnosis - I said "no thank you". Found a scanner that would read oil pressure and found pressure to be slightly over 22 PSI at idle, about 35 PSi at 1000 RPM's and 42-46 during normal driving. Drove for another 5000 miles and the code never returned. Changed the oil at 125,000 miles and within about 800 miles again get code P0521. Bought a cheap ELM327 OBDII reader that I could connect to my phone and monitor oil pressure while driving - once again oil pressure shown to be satisfactory. Drove another 700 miles before getting the code again. Shortly after I also got a quick message on the DIC stating Oil Pressure Low - shut down engine. Hooked up my ELM327 again and it showed oil pressure very erratic going from 45+ PSI t to 0 and anywhere in between. I was convinced that the issue was real and got gaskets, orings, etc. in preparation to drop the pan and further diagnose the issue. Just for shits and giggles, I also bought a TEE where i could install a mechanical test gauge just below the sending unit. At idle, the gauge showed 24 PSI while OBDII showed 20.9. At 1000 RPM's, gauge showed 37 PSI while OBDII showed 34.2 PSI. During normal driving both in excess of 42 PSI. Note that the mechanical gauge was very steady whereas the OBDII reading fluctuated by about 5 PSI. After driving the car for about 20 minutes, the mechanical gauge remained as stated above (good) while the OBDII became very erratic going from 45+ to 0 and anywhere in between again. Even got the DIC message stating Oil Pressure Low. So this confirmed to me that the oil pressure was good and the problem is somewhere else.

Step one was to replace the sensor again with another new GM 12621234. So far, 500 miles on the new sensor with no codes and much steadier oil pressure indication. To early for me to say for sure, but it certainly appears that the sensor was the issue. Find it hard to believe that a new sensor would fail in such a short period of time, but all info points to that. I'll keep you posted as i rack up more miles.
TEE Connection.jpg
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Idle.JPG (1.57 MiB) Viewed 40 times
1000 RPMS.JPG (1.77 MiB) Viewed 40 times
Twin 2012 9C1's
1991 R2500 Banks Turbo Diesel Suburban
1990 V2500 Banks Turbo Diesel Suburban
1991 GMC Syclone
1986 Buick Grand National

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