P0521 Oil Pressure Low - 2009 Chevrolet Silverado 6.0L Engine Diagnosis and Repair Tips

P0521 is indeed the correct code — always include the prefix (e.g., P0521) to avoid confusion with similar codes like P0522 or P0523. The fact that both dealerships are seeing this issue suggests a potential inconsistency in diagnosis. My hypothesis: The second dealer may have identified an issue that the original dealership overlooked — possibly related to the valve lifter oil filter, which is separate from the main engine oil filter. A clogged passage or inadequate flow could trigger P0521 even if overall engine oil pressure appears normal. Check for relevant TSBs and PIPs (Product Improvement Proposals) specific to the 2009 Chevrolet Silverado 6.0L, especially those related to oil pressure sensors or valve lifter systems. Codes such as PIP5276F or PIP4786C may be associated with this issue — verify if your engine has any of these. If the valve lifter filter was replaced at both dealerships, that could point to a deeper blockage in the oil passage system.

Thank you for the insight. I will bring this information to the first dealership when I return with the truck and request a full TSB review and diagnostic check on the valve lifter oil filter system.

After reviewing my records, I confirm that the valve lifter oil filter was replaced twice — both times by different dealerships. It appears to be a small, dedicated filter located near the engine block. Given that it's been changed multiple times without resolving P0521, this strongly suggests either a persistent blockage or a sensor issue downstream of the main oil system.

I strongly recommend addressing this as soon as possible. If the valve lifter filter has been replaced twice by different mechanics, the next step should be to verify true engine oil pressure using a mechanical gauge installed directly at the engine's oil passage — not just readings from the dashboard or sensor. This is critical because many P0521 cases are misdiagnosed due to reliance on indirect sensors. There are known long-term issues in 2009 Silverado 6.0 engines where sludge buildup or restricted oil flow through the valve lifter filter leads to false low-pressure readings, even when main engine pressure is normal. Early detection can prevent expensive internal engine damage.

Thank you — the second dealership did perform a true oil pressure test using a mechanical gauge and confirmed that engine oil pressure was within specifications at the main oil pump outlet. This makes it even more likely that the issue lies in the valve lifter filter or sensor calibration, not actual low pressure.

Do you have any history of previous engine repairs? For example, was there a prior engine replacement? I considered checking this but it's difficult to verify without access to the vehicle’s service records. A practical next step would be to test oil pressure at both the main oil filter and the valve lifter oil filter — comparing readings between these two points can reveal if there is a blockage or restriction in the passage.

No known engine replacement history. The second dealer conducted a full GM service history check and found only minor warranty-related work (such as oil changes), with no major repairs or engine replacements prior to my ownership.

I will take your advice and bring the vehicle back to the original dealership, where I purchased it. I’ll request a full diagnostic including TSB review and physical oil pressure testing at both filter locations. Thank you for all the helpful input.